E Book - ETEMAS 2023.pdf

Emerging Trends in
Engineering, Management,
Arts and Science

Chief Editors
Dr. R. Rajkumar
Dr. B. Ramesh
Mr. Suresh D.
Dr. A. Kadirvel
Dr. M. Mekala
Editors
Dr. Kavita Khatana
Dr. Neeta Dhusia Sharma
Dr. R. Madhusudhanan
Dr. Roopa Shettigar
Dr. Joy Mukhopadhyay
TECHPRESS
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E-mail: techpress19@gmail.com
Emerging Trends in
Engineering, Management,
Arts and Science

Published by :
TECH PRESS
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Mob.: + 91 9540220106, 8799747108
E-mail: techpress19@gmail.com
Emerging Trends in Engineering, Management, Arts and Science
© Editors
First Edition: 2023
ISBN : 978-93-91697-09-9
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(v)
Preface
We are glad to present the book entitled Emerging Trends in Engineering,
Management, Arts and Science to the students, faculty members and
researchers of Engineering, Management, Arts and Science. We have observed
that eminent professors and active researchers from various technical
institutions across the Nation contributed to the book chapters which are
focused on state-of-the-art areas related to Electrical and Electronics
Engineering, Computing Sciences, Civil Engineering and Mechanical Sciences,
Management, Arts and Science.
We hope the readers benefit from the research problems addressed in
the book. We are thankful to all the authors and publisher who have helped
to bring out the First Edition of the book Emerging Trends in Engineering,
Management, Arts and Science.
Chief Editors
Dr. R. Rajkumar
Dr. B. Ramesh
Mr. Suresh D.
Dr. A. Kadirvel
Dr. M. Mekala
Editors
Dr. Kavita Khatana
Dr. Neeta Dhusia Sharma
Dr. R. Madhusudhanan
Dr. Roopa Shettigar
Dr. Joy Mukhopadhyay

Contents
Preface (v)
1. A Survey on PAPR Reduction Techniques for MIMO-OFDM
Wireless Communication System 1
–Dr.Maddala Vijayalakshmi
2. Design of Sliding Contact and Rolling Bearings 15
–Dr. B. Ramesh
3. Design of Keys, Couplings and Joints 37
–Dr. B. Ramesh
4. Color Science and Its Application in Paint Industry 60
–Joy Mukhopadhyay
5. Energy Management in Institutional Buildings through
Efficient Lighting Systems 67
–Anuja N, AmuthaPriya N, Sree Rameswari A, Jeganmurugan P
6. Knowledge Transfer through Transfer Learning– A
Machine Learning Approach for Image Classification 84
–Mr. Ebin P.M, Ms. Kavitha Nair R, Ms. Jimsha K Mathew
7. IoT Based Energy Meter Monitoring System 93
–Srisailapu D Vara Prasad, P Venkat Reddy,
Dr.Ravi Teja Bhima, Srinivasa Rao Dhanikonda
8. Foundations of Data Science 101
–Dr. K. Meena1, Dr. J.Dhivya
9. Mathematics Towards Data Science 108
–Dr. J.Dhivya, Dr. K.Meena
10. Single Window Monitoring of all Rural Welfare
Development Schemes 113
–Dr.N.Revathy, Mrs.B.Sathyabama, Mr.S.Lalith Kumar,
Mr.M.Hussain Shariff
11. Surface Engineering for Enhanced Tribological Performance 124
–Dr. Edward Anand.E.
(vii)

12. Introduction to Block Chain and 5G Enabled IoT Devices 137
–Dr.R.Anusha, Ms.A.Angayarkanni, Ms.R.Gavoury
13. Hybrid Evolutionary Algorithms for Localization Error
Minimization in Wireless Sensor Networks 169
–Dr. S. Sivakumar
14. A Systematic Literature Review About Big Data Analytics 186
–Dr V Kavitha, Mrs P Hemashree, Mr N S Kiran, Ms M Kiruthika
15. IoT Based Auto Climate Monitoring System with Arduino
UNO and Thingspeak 197
–Mrs. B. Sathyabama, Dr. N. Revathy, Ms. Megha Manoj,
Ms. Midhuna Mohanan
16. Anti Malware Browser to Detect Fake URL Using
Random Forest Model in Machine Learning 205
–Dr. N. Revathy, Mr. A Ganesan, Ms. C T Arunima,
Mr. G. Gowtham
17. Performing NLP for Finding Semantic Drift Using
Naïve Bayes Machine Learning 220
–Ms. A. Uma Maheswari, Dr. N. Revathy
18. Protection of Child Rights 229
–Dr. V. Kavitha, Ms. R. Pavithra, Mr. G. Kavinvijayraj,
Mr. G. Kathirvel
19. SoC Implementation using FPGA for ECG Signal Analysis 238
–Jeslin Libisha J, Dr. L. Suganthi, Ms. B. Divya
20. Work Life Balance of Police in India 250
–Mrs. R. Banurekha, K. Saranya, S.S. Sachin, M.A. Praveen
21. Gender Difference in the Perception of Work-Life Balance 258
–Praveen.P, Pradeep.P, Santhiya Ajith. A , Vasikaran. K
22. Work Life Balance of Female Teachers 265
–Mrs.R.Banurekha, R. Sandhiya Sri, M.A. Priyadharshini,
M. Martin Deeepak, S.Robin
23. Leverage Analysis 273
–Dr. Roopa Shettigar
24. Drone Security and Privacy Solutions Using Blockchain 291
–Dr. C. Krishna Priya, Nazeer Shaik, Dr. P. Suma Latha
Dr. B. Hari Chandana
25. Harnessing the Synergy of Quantum Computing and
Artificial Intelligence: Unlocking New Frontiers in
Computation and Learning 326
–Nazeer Shaik, K. Venkatesh, K. Kondanna, Dr. P. Chitralingappa
(viii)

26. Machine Learning Based Cyber-attack Resistant Microgrid
System with IRNSS Synchronization 359
–M Balasubbareddy , P. Kowstubha, A. Supraja Reddy
and P. Sathish4
27. Transforming the Mechanical Engineering Industry with
Intellectual Internet of Things: A Review of its Benefits and
Potential Challenges 367
–Dr. Shivaleela Arlimatti, Dr. Suresh D. Mane
and Mr. Ganesh Rathod
(ix)

1
1
A Survey on PAPR Reduction Techniques
for MIMO-OFDM Wireless Communication
System
–Dr.Maddala Vijayalakshmi1
Abstract
The high PAPR value is one of the major problems present in the MIMO-
OFDM system. Because of high PAPR value, power amplifiers drive into
nonlinear region and generate out of band frequency components. The
orthogonality between the subcarriers is disturbed and the signal cannot be
reconstructed perfectly at the receiver section which degrades the BER
performance of MIMO-OFDM system. High resolution ADC converters are
required for perfect recovery of the signal which increases the complexity of
the MIMO-OFDM system. In the literature many PAPR reduction techniques
are proposed to overcome all these problems. These are mainly classified into
Distortion less, Distortion, coding techniques. The various existing techniques
to enhance PAPR reduction are specified in the following sections.
Key Words: MIMO: Multiple Input and Multiple Output, PAPR: Peak To
AveragePower Ratio, PTS: Partial TransmitSequence, SLM: Selective Mapping.
1. DISTORTION LESS PAPR REDUCTION TECHNIQUES
In distortion less techniques, PAPR is minimized without disturbing the
input signal. In this classification PTS, SLM, TR are the major techniques for
minimizing PAPR value which are explained in the following sections.
1 Assistanat professor, G.N.I.T.S, Hyderabad
E-mail: Vijayap03@gmail.com

2 Emerging Trends in Engineering, Management, Arts and Science
1.1 Partial Transmit Sequence
In PTS method, the partitioned input data is multiplied with the phase
factors to reduce the PAPR. The complexity is high in choosing the optimum
phase factor set from a large number of phase factor set. For reducing this
complexity, many optimization algorithms are used in the PTS technique.
Different population based optimization algorithms like DE, Adaptive DE,
Cuckoo, ABC ACO, PSO are exist in the literature to minimize the complexity
of PTS system which are specified as follows.
1.1.1. Optimization Algorithms
Differential Evolution Algorithm
DE is an effective and robust population based stochastic exploration
method and it is used to solve difficulties in continuous space. It has been used
in engineering and scientific fields. Hocine Ait Saadi et al [1] have proposed DE
algorithm for reducing the complexity of searching optimum phase factors
vector and to improve the PAPR performance of PTS. DE based PTS attains
the excellent PAPR reduction performance with a minimum computational
complexity. This proposed scheme is highly applicable for the large data rate
OFDM systems because the computational complexity reduction ratio (CCRR)
is proportional to the number of orthogonal subcarriers.
Saurav Ghosh et al [2] have proposed an adaptive DE technique for
reducing the complexity of acquiring best phase factors vector in PTS. In this
proposed method, DE algorithm is modified by employing novel mutation,
crossover and parameter adaptation strategies (MDE_pBX) for a PTS of a sub-
optimal type to minimize the PAPR of the OFDM signal. Based on the results
obtained after simulation MDE_pBX provides efficient phase factors set to lower
the PAPRwhen compared to other important DE and PSO versions like CLPSO,
JADE and SaDE.
Cuckoo Search Algorithm
The CS algorithm is originally implemented by Yang and Deb. It is a
robust algorithm for optimization which employs the offensive breeding
techniques of the cuckoo bird. In the literature Cuckoo Search technique is
used to reduce the complexity of PTS system.
Yüksel Tokur Bozkurt [3] et al have proposed Cuckoo search algorithm
for reducing the complexity of acquiring optimum phase weight vector in the
PTS technique. The setof phase factors arerepresented bythe eggs of the cuckoo
bird. The CS based PTS has superior PAPR reduction performance when
compared to RS based PTS, Optimum PTS, PSO based PTS in the OFDM system.
R. Manjith et al [4] have implemented Modified CS (MCS) based PTS technique

3
to lessen the PAPR value of MIMO-OFDM signals while minimizing the
computational complexity. Thefollowingarethe changes made to CS technique:
1. In the traditional CS, the parameter ‘á’ value is constant, but in the
MCS, ‘á’ varies inversely with the number of Generations G. The
constant ‘á’ is added to speedup the searching process for obtaining a
set of phase factors which resides in the surrounding of the best phase
factors set.
2. In this MCS, for each and every phase vector discover probability is
calculated and based on this probability top ‘ S’ number of phase
vectors are selected from the ‘N’ number of phase vectors in the first
phase. From the remaining phase vectors set choose second nest
randomly for all the top S phase vectors and by using these phase
vectors a new phase vector is produced.
3. The last change implemented in this method is, if the set of phase
factors are not minimizing the PAPR value then these are to be
eliminated immediately. An MCS based PTS technique can effectively
minimize the computational complexity for sub blocks of larger size
and also offers more PAPR reduction, but the BER performance of
MCS based PTS is degraded slightly compared to optimum PTS.
X. Yang and Suash Deb et al [5] proposed a new meta heuristic technique
named Cuckoo search to resolve various optimization problems. The PAPR
performance of this proposed algorithm has been evaluated and compared
with other existing algorithms such as PSO, Genetic algorithms. According to
the simulation results, Cuckoo search based PTS technique has superior PAPR
reduction performance than the existing algorithms for objective functions of
multimodal type.
Rohit Salgotra et al [16] proposed three modifications to the existing
cuckoo search algorithm to enhance the properties of exploration and
exploitation. All these three modified versions incorporate Cauchy operator
for finding the correct step size in place of Lévy flights to effectively analyze
the search space. In addition to these modifications, the proposed technique
utilizes two latest concepts, population division and generation division in CS
such that balancing of the exploration and exploitation characteristics is
achieved. These modifications have produced significant enhancement of the
PAPR reduction performance of CS based PTS when it is tested on different
bench mark functions. M.Mareli et al [7] have developed three modifications
to the Cuckoo Search algorithm based on the switching parameters of
dynamically increasing nature. These three modified cuckoo techniques are
tested on ten different mathematical functions. The PAPR reduction
performances of these three techniques are compared with the Cuckoo
technique and switching parameters of dynamically decreasing nature. Based
on the simulation results these new techniques outperformed than the Cuckoo
search technique.
A Survey on PAPR Reduction Techniques for MIMO-OFDM Wireless . . .

ABC Algorithm
ABC is a recently proposed swarm-based optimization algorithm that
imitates the honey bees foraging manner. This algorithm convergence speed is
more, flexibility is also high. In a continuous search field, the performance of
ABC algorithm is better when compared to other techniques and it can also be
applied to problems related to unconstrained field. Karaboga Dervis et al [8]
extended ABC algorithm for constrained optimization difficulties. Initially,
ABC technique is applied to the unconstrained optimization problems. The
modified ABC algorithm performance has been compared with state-of-art
problems and it is concluded that it can also be used efficiently for constrained
optimization problems. According to the simulation results its PAPR reduction
performance is better than DE, PSO algorithms. Gaowei YAN et al [9] have
improved the performance of ABC algorithm by increasing the number of scout
bees, rational using of global optimum value and a chaotic search. In this chaotic
search ABC, onlooker bees employ chaotic sequence to improve the local
searching pattern and also trapping in a local minima is being avoided. This
technique is applied to tune the PID control parameters and according to the
simulation results it gives high accuracy, low rise time etc.
Yunfeng et al [10] have developed a simple, efficient and hybrid algorithm
of ABC technique and DE/best/1 mutation scheme. This proposed technique
changes employee bees and onlooker bees search pattern. In general, the ABC
technique gets stuck easily while solving multimodal problems of complex
type, since its search pattern is not efficient at exploration and efficient at
exploitation. Moreover, the convergence speed is less when compared to DE
and PSO techniques. DE/best/1 mutation technique is efficient in exploitation
phase, so the proposed method overcomes the drawbacks of ABC technique.
The proposed hybrid method has more convergence speed and the solutions
are also more accurate when compared to the ABC technique. Necmi TAS et al
[11] have implemented ABC algorithm for improving the PAPR reduction
performance of PTS in MIMO OFDM system. The ABC based PTS, PAPR
reduction performance was compared to conventional PTS, random search
strategy (RS-PTS) and optimum PTS. In the simulation process, travelling wave
tube power amplifiers (TWTA), Solid state power amplifiers (SSPA) are used
and their performances are also compared. At receiver input, AWGN is added
to the received signal and also the Rayleigh flat fading channel model is
considered in the simulation. According to the simulation results, the ABC
based PTS is greatly successful in minimizing the PAPR with lower complexity
and also got better BER performance.
PSO Algorithm
Jyh-Horng Wen [12] have proposed PSO algorithm for improving the
PAPR reduction performance of OFDM system. In PSO technique, swarm

5
represents the group of phase vectors and each phase vector is called particle.
This PSO technique resembles the searching for flowers by a group of bees.
The searching process efficiency is depending upon the number of bees
participated and velocity of the bees. The velocity of the bee is changed
dynamically based on its own velocity and the velocity of the best bee. This
proposed technique obtains the best phase vector which provides the high
PAPR reduction with a minimum number of iterations.
Necmi TAS¸PINAR1 et al [13] have proposed back tracking search
algorithm (BSA) to lessen OFDM signal PAPR value with PTS technique. BSA
is lately proposed evolutionary algorithm for obtaining solutions to the real
valued optimization problems and also it consist some improvements
compared to other evolutionary algorithms. By adding this technique,
sensitivity to control parameters is reduced and convergence speed is also
raised. The CCDF of BSA based PTS is lower than the ABC based PTS, DE
based PTS, PSO based PTS and also achieved better BER performance.
Sonia Singla et al [14] have proposed Ant Colony Optimization (ACO)
algorithm to improve the performance of PTS for minimizing the PAPR value
in OFDM systems.ACO is implemented basically to solve complex
combinatorial difficulties. This algorithm basically imitates the ant’s behaviour
in finding food. The ants generally produce pheromoneand dropon the ground
when they are moving. By using trail pheromone, ants create a path to the
food source from the nest and other ants can follow the same path. By nature
ants can choose the best path from all available paths to reach the food source.
In ACO based PTS, the number of ants represent the set of phase vectors. The
best food source represents the phase vector which gives the lower PAPR value.
ACO based PTS minimizes the high PAPR probability of the OFDM system.
1.1.2 Different Partitioning Techniques
In the PTS technique, the PAPR reduction performance depends on the
numberof blocks and the method of dividingthe input data into several blocks.
Zeyid T.Ibraheem et al [15] have proposed different partition sizes to the input
symbol sequence in PTS technique for the PAPR reduction of OFDM system.
In the traditional PTS technique, input data sequence is divided into blocks
before multiplying with the phase vectors. In this paper by varying the size of
the input block, the PAPR performance of the MIMO-OFDM system with PTS
is analyzed and also applied different partitioningtechniques in the simulation.
Based on the results obtained after simulation, it is concluded that using smaller
block size the PAPR performance with an adjacent partitioning technique is
reached to the PRP based PTS and is not changed in IP based PTS. It is observed
that by increasing the number of blocks, the PAPR reduction performance of
PTS is improved in MIMO-OFDM system.
P. Mukunthan et al [16] have proposed interleaved partitioning technique
and pulse shaping for improving the PAPR performance of PTS in MIMO-

OFDM system. By using raised cosine pulse shaping filter,the correlation value
is minimized between the samples of OFDM signal and at the same time, the
orthogonality between the sub carriers is maintained. By properly selecting
sub block size and number of sub carriers this method eliminates the necessity
of more number of IFFTs as required in traditional PTS.
1.1.3. Low Complexity Techniques
In PTS technique, input data is partitioned and convertinto parallel blocks,
then multiplied with set of phase factors to lessen the PAPR of the MIMO-
OFDM signal. For all these parallel sub blocks IFFT is performed which is a
very complex process since it requires more number of multiplications and
additions. To lower the number of multiplications and additions various
solutions are proposed in the literature.
Lingyin et al [17] proposed low complexity PTS for reducing PAPR in
MIMO-OFDM system. In this method two properties of IFFTs are employed
to lower the number of multiplications and additions. The first property used
in this is byconverting frequency domain sequence into time domain sequence,
the computational complexity is reduced. The second property used in this is
by rotating the signal phase in the time domain is similar to the cyclically
shifting the sequence in the frequency domain. By applying these two
properties, the proposed scheme computational complexity becomes less when
compared to that of C-PTS but at the same time, PAPR reduction performance
is unchanged.
Yun Li et al [18] have proposed an alternate and cooperative PTS scheme
for the reduction of PAPR in STBC MIMO-OFDM system. In Alternate PTS,
every alternate sub block is not multiplied with the weight coefficients and the
remaining blocks are multiplied with the weight coefficients. In Co-operative
PTS, by applying conjugated relationships to the weighting coefficients, the
required number of multiplications and additions are minimized. The PAPR
reduction performance of the STBC MIMO-OFDM system with proposed
technique is similar to the PTS but at the same time, the complexity is minimized
by five times.
Wang et al [19] proposed a new technique that linearly combines the
OFDM signal and its cyclically shifted versions of the OFDM signals. The
cyclically shift operation is used to produce different phases and time delays
of a given signal. This proposed scheme has lower complexity when compared
to that of the SLM technique, but it has some degradation in BER performance.
1.2 Selective Mapping
It is one of the popular distortion less methods for minimizing the MIMO-
OFDM signal’s PAPR value. In this technique, input data is not divided into
sub blocks and it has more complexity. To overcome the high complexity,

7
various techniques are suggested in the literature. Kavitha Mhatre et al [20]
have evaluated the PAPR performance of the OFDM system with SLM
technique. In this paper some important concepts related to other PAPR
reductiontechniqueslike clipping, PTS, coding schemes, Tone injection method,
concepts related PAPR, performance metric used for PAPR are mentioned.
According to simulation results, it is observed that the PAPR performance of
the OFDM system with SLM is improved by taking more number of phase
sequences. It is also observed that by increasing the number of subcarriers the
PAPR reduction performance is diminished.
Necmi Ta¸spýnar et al [21] have proposed modified ABC technique,
parallel ABC techniques for minimizing the complexity of SLM techniques.
SLM is an efficient technique since it provides good PAPR reduction
performance without distorting the signal, but its computational complexity
is high. Parallel ABC based SLM provides significant PAPR reduction and better
BER performance with the minimum computational complexity in MIMO-
OFDM with the Alamouti SFBC system.
1.3 Tone Reservation Technique
Tone Reservation (TR) technique isimplemented to combat PAPR problem
by retaining a few sub carriers (tones) in the frequency domain to produce a
cancellation signal in the time domain. This cancellation signal can be used to
remove the high peaks present in the OFDM signal. Developing a signal in the
time domain using few sub carriers increases the computational complexity.
Carole A. Devlin et al [22] have proposed Gaussian pulse based tone
reservation technique to minimize the PAPR of OFDM signal . In this proposed
method, Gaussian pulse is generated from a few subcarriers and is used to
cancel the peak value if it exceeds the threshold limit. By adding Gaussian
pulse, the PAPR valueof the OFDM signal reduces withvery low computational
complexity.
Lei Guan et al [23] have proposed a powerful technique called two-
threshold parallel scaling for modifying the initial Gaussian pulse based TR
technique to minimize the PAPR value of the OFDM signal. When compared
to conventional methods, this proposed technique effectively minimizes the
complexity of hard ware implementation, cost and also lessen the signal
processing delay within two iterations. According to the simulation results,
this method reduces the PAPR value of the OFDM signal significantly with
fewer tones compared to the other systems and it is more suitable for any
OFDM based communication systems like DVB etc.
2. CODING TECHNIQUES
To lessen the PAPR of MIMO-OFDM signal, various coding schemes are
proposed in the literature. These coding techniques are applied to the input

data before performing IFFT operation.
Dr Uday Wali et al [24] have compared the performance of LDPC codes,
convolutional codes and turbo codes for PAPR reduction in MIMO-OFDM
system. LDPC code is a powerful technique for channel coding as it has many
advantages like the channel capacityapproaches the Shannon’s capacity,allows
Parallel implementation, suitable for both low data rates and high data rates
based on the modulation type, good PAPR reduction performance, etc. The
PAPR performance of LDPC codes in OFDM system is analyzed for various
situations and it is observed that, it outperforms when compared to the turbo
codes. DaimingQu et al [25] proposed invertible subset LDPC codes to improve
the PAPR reduction performance of the OFDM system. Forimproving the error
correction capabilities of IS-LDPC codes, a new technique called modified
progressive edge-growth construction is implemented and by using Tanner
graphs its effectiveness is verified. The proposed method has improved error
correction capability and it also approaches the performance of LDPC codes
with PEG algorithm. The proposed scheme PAPRreduction capability is similar
to the PTS system with low complexity and because of this it can be implemented
more in high data rate communication systems with multi carriers.
3. DISTORTION METHODS FOR PAPR REDUCTION
In distortion techniques like Clipping and Filtering,Companding etc,
PAPR is reduced, but the received signal is distorted.
3.1. Clipping and Filtering Technique
The clipping method is a nonlinear PAPR reduction scheme, in which the
peak of the OFDM signal is clipped if it exceeds a particular threshold value.
Wang et al [26] proposed an Iterative Clipping and Filtering technique where,
all iterations are expressed as a convex optimization techniques and the optimal
frequency response filter is designed to reduce the signal distortion such that
PAPR value is minimized for each of the OFDM symbol. This method provides
a PAPR reduction in just one or two iterations while the same performance in
a conventional technique requires eight to sixteen iterations. Victor Cuteanu et
al [27] proposed sequential tone reservation with clipping for diminishing the
OFDM signal’s PAPR value. This new hybrid PAPR reduction technique
consists of both the advantages of linearity from the TR method and low
computational complexity from the clippingtechnique. This combined method
provides a better PAPR reduction in OFDM system, without degrading the
BER performance.
Victor Cuteanu et al [28] proposed a hybrid technique of SLM method
combined with a clipping method for reduction of PAPR in the OFDM system.
Initially, data signal is clipped and after that it is applied to the input of SLM
system. As per simulation results, PAPR of the OFDM signal decreases and
needs only a few iterations to recover the signal at receiving end.

9
3.2. Companding
The Companding scheme effectively compresses the larger signals and
enhances the small signals to achieve PAPR reduction.The Companding
Transform can be used to limit PAPR statistics for an arbitrary number of
carriers, irrespective of the frame format and constellation type.
Stephan p. DelMarco et al [29] have developed new companders for the
PAPR reduction of the OFDM signal. The designing of these companders is
based on the peak values of the OFDM signal. These new companders can
workin the operatingcondition space, where otherexisting companders cannot
work. The PAPR reduction performance of this compander in OFDM system
is better than the other existing companders.
Aburakhia et al [30] proposed a Linear Companding Transform (LCT)
with two inflexion points to scale different signal levels independent of one
another. Based on the simulation results of this proposed LCT and NLST on an
AWGN channel it was inferred that LCT performs better in terms of PAPR
reduction and BER performance.
4. HYBRID METHODS FOR PAPR REDUCTION
P. Mukunthan et al [31] have proposed a hybrid method to lessen the
MIMO-OFDM system PAPR value. In this hybrid method, initiallydata is coded
using Reed-Muller coders with complementary sequences, then applied to the
input of the PTS block. The symbol sequences applied to the input of the PTS is
separated into real and imaginary parts, and these are multiplied with phase
factors. In the simulation, performance of the proposed hybrid method is
compared with that of Turbo codes PAPR performance. The turbo based PTS
has good PAPR performance, but as the number of orthogonal sub carriers
increases the PAPR value of the MIMO-OFDM signal increases. By using the
proposed method, the limitation of Turbo codes based PTS is eliminated and
at the same time it has improved PAPR reduction performance.
Prabal gupta et al [32] proposed a hybrid method for reducing the MIMO-
OFDM signal PAPR value. In this initially data is encoded with BCH codes,
and after that modulated, then partitioned into blocks. These sub blocks of
data sequence are applied to the input of PTS to minimize the PAPR value of
the OFDM signal. At the receiver, initially received symbols are multiplied
with the same set of phase vectors, then demodulated and after that syndrome
decoding is applied to decode the data. The PAPR reduction performance of
this combined method is improved but the complexity is not changed when
compared to the original PTS system.
Osamu Muta et al [33] have proposed a hybrid method for reducing the
PAPR of OFDM system. In this initially data is encoded with LDPC codes, and
after that modulated, then partitioned into blocks. These sub blocks of data
sequence are applied to the input of PTS to minimize the PAPR value of the

OFDM signal. At the receiver, received symbols are multiplied with the same
set of phase vectors, then demodulated and afterthat LDPC decoding is applied
to decode the data. The PAPR reduction performance of this combined method
is improved without significant degradation in the BER performance. In this
hybrid method, both systematic and non-systematic LDPC codes can be used.
Li Li, Daiming Qu et al [34] have proposed two greedy algorithms for
optimizing the number of partitions in PTS to enhance the OFDM system
performance for PAPR reduction. In this method, LDPC coded output is
partitioned into sub blocks and these blocks are applied to the input of PTS
block. For partitioning the coded block, pseudo random partitioning technique
is used, but its performance is suitable only for less number of partitions. By
employing iterative partitioning and greedy partitioning techniques, the
combined system’s PAPR reduction performance is improved even for the large
number of partitions. The proposed method’s convergence speed is more and
also provides lower complexity for decoding.
Kamal singh et al [35] proposed a hybrid method to lessen the PAPR of
MIMO-OFDM signal. In this method, initially the data symbol sequence is not
partitioned and is applied to the SLM system. The best phase sequence which
minimizes the PAPR of the input symbol sequence is obtained in the SLM
system and it is multiplied with the input sequence. To further enhance the
PAPR reduction performance, the output of SLM is partitioned into sub blocks
and is applied to the input of the PTS system. According to the simulation
results, this hybrid method enhances the PAPR performance of the MIMO-
OFDM system when compared to the SLM, PTS and iterative flipping
techniques. The complexity of this hybrid method increases as the number of
partitions increases in the PTS system.
Christian Siegl et al [36] proposed a TR technique combined with the
SLM technique for diminishing the PAPR value of the MIMO-OFDM signal.
In the TR method few number of sub carriers are reserved to generate a peak
cancellation signal. By using this technique, the PAPR value of the OFDM signal
is minimized. In SLM technique, the input symbol sequence is multiplied with
the phase factors set to minimize the PAPR value of the OFDM signal. By
combiningthese two techniques, the PAPR value is effectively minimized when
compared to the individual techniques, clipping technique.
Eugen-Victor Cuteanu et al [37] proposed Tone reservation with Active
Constellation Extension technique for lessening the PAPR of the OFDM signal.
The simulation results show that the ACE technique produces higher PAPR
reduction for various OFDM frame formats. The PAPR reduction performance
is further improved if TR block is combined with the ACE block.
Leman Dewangan et al [38] have evaluated the performance of PAPR
reduction techniques like clipping peak windowing, interleaving, coding,
companding, PTS, SLM and TR in the LTE-OFDM system. According to
simulation results, the signal is distorted in case of clipping technique and

11
complexity increases, no data loss occurs in case of PTS, SLM and coding
techniques, power increases in ACE, TR and TI techniques.
5. CONCLUSIONS
In Literature, various techniques are proposed for reduction of PAPR in
MIMO-OFDM systems. In the PTS, SLM techniques, PAPR is minimized
without distorting the signal, but the computational complexity is increased.
To reduce this complexity, various techniques are proposed but still it is not
minimized. Various coding techniques are proposed to minimize the PAPR of
MIMO-OFDM system but data rates are minimized. Distortion techniques like
clipping, companding etc are proposed for reducingthe PAPR of MIMO-OFDM
system. Various new techniques are proposed like DFT Based OFDM, filtered
OFDM, precoded OFDM etc for reducing PAPR of MIMO-OFDM system.
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2. Saurav Ghosh1, Subhrajit Roy1, Swagatam Das1, Ajith Abraham2 and Sk.
Minhazul Islam1, “peak to average power ratio reduction in OFDM systems
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3. Yüksel Tokur Bozkurt,Necmi Taþpýnar,“PAPR reduction in OFDM systems
using partial transmit sequence combined with Cuckoo search optimization
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5. X. Yang and Suash Deb, “Cuckoo Search via Lévy flights,” 2009 World
Congress onNature & BiologicallyInspired Computing (NaBIC), Coimbatore,
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10. Yunfeng Xu, Ping Fan, and Ling Yuan, “A simple and Efficient Artificial Bee
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Ant Colony Optimization”, International Journal of Advanced Research in
Computer and Communication Engineering, Vol. 2, Issue 8, August 2013.
15. Zeyid T.Ibraheem,Md.Mijanur Rahman,S.NYaakob,Mohammad Shahrazel
Razalli,Rasim A.Kadhim,”Performance of PTS Techniques with Varied
Partition size in PAPR Reduction of OFDM System”, Procedings of
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technology,IEEE,September,2014.pp no.21-25.
16. P.Mukunthan and P.Dananjayan,” A Modified PTS Combined with
Interleaving and Pulse Shaping Method Based on PAPR Reduction for STBC
MIMO-OFDM System”, WSEAS Transactions on Communications, Issue
3,Volume 12,March 2013.PP no 121 to 131.
17. L.Wang,Xinghai Yang and Yutai Wang,”PTS scheme with low complexity
IFFTs for PAPR reduction in SISO/MIMO OFDM,”2013 IEEE 4th
International
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Beijing, 2013, pp.181-184.
18. Yun Li, Mingyu Gao and Zhiqiang Yi, “A cooperative and alternate PTS
scheme for PAPR reduction in STBC MIMO-OFDM system,” 2012 IEEE 14th
International Conference on Communication Technology, Chengdu, 2012, pp.
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19. Wang, Xinghai Yang and Yutai Wang, “PTS scheme with low complexity
IFFTs for PAPR reduction in SISO/MIMO OFDM,” 2013 IEEE 4th
International Conference on Electronics Information and Emergency
Communication, Beijing, 2013, pp. 181-184.
20. Kavitha Mhatre,Uday pandit Khot, “Efficient selective mapping PAPR
reduction technique, “2015,International conference on Advanced Computing
technologies and Applications,2015,pp.620-627.
21. Necmi Ta¸spýnar and Mahmut Yýldýrým, Member, IEEE, “A Novel Parallel
Artificial Bee Colony Algorithm and its PAPR Reduction Performance Using

13
SLM Scheme in OFDM and MIMO-OFDM”, IEEE Communications Letters,
Vol. 19, No. 10, Oct 2015.
22. C. A. Devlin, A. Zhu and T. J. Brazil, “Gaussian Pulse Based Tone Reservation
for Reducing PAPR of OFDM Signals,” 2007 IEEE 65th Vehicular Technology
Conference - VTC2007-Spring, Dublin, 2007, pp. 3096-3100.
23. Lei Guan,AndingZhu, “Guassian pulse based Two-Threshold parallel scaling
Tone Reservation for PAPR reduction of OFDM signals, “Internationaljournal
of Digital multimedia Broadcasting, vol. 2011,pp.1-9.
24. Uday Wali,B.K Shiragapur,Mahesh Taralkar,Kalyani G.Fule,”PAPR
Reduction Using LDPC for MIMO-OFDM systems”,IJAREEIE,Vol.3,Issue
4,April 2014,pages 9211-9217.
25. Qu,Daiming&Li,Li&jiang,Tao.Invertible subset LDPC code for PAPR
reduction in OFDM systems with low complexity.Wireless Communication,
IEEE Transactions.2014.
26. Wang Y.-C. and Luo Z.-Q.,2011.”Optimized iterative clipping and filtering
for PAPR reduction of OFDM signals, IEEE transactions on
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signals using sequential Tone Reservation-clipping Hybrid
scheme.”proceedings of SPAMEC 2011,cluj-Napoca,Romania.
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Reduction in OFDM Signals Using Amplitude Distribution Modification”,
IEEE Transactions on Broadcasting, Vol 60,No.1,March 2014,pp.102-109.
30. Aburakhia S.A., Badran E.F,Mohamed D.A.E, Linear companding Transform
For the reduction of peak-to- average Power ratio of OFDM signals ,”IEEE
transactions on Broadcasting ,Vol.55,No.1, 2009,pp.155-160.
31. P. Mukunthan and P. Dananjayan, “Modified PTS with FECs for PAPR
reduction in MIMO-OFDM system with different blocks and
subcarriers,” 2011 International Symposium on Humanities, Science and
Engineering Research, Kuala Lumpur, 2011, pp. 89-94.
32. Prabal gupta, B.Arun Kumar, Sandeep Kumar Jain ,”Peak to Average Power
Ratio Reduction in OFDM UsingHigher Order Partitioned PTS sequence and
Bose Chaudhuri Hocquenghem Codes”,SPACES-2015,KLU,PP.443-447.
33. Osamu. Muta and Y. Akaiwa, “Peak Power Reduction Method Based on
Structureof Parity-Check Matrix for LDPCCoded OFDM Transmission,” 2007
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34. L. Li and D. Qu, “Joint Decoding of LDPC Code and Phase Factors for OFDM
Systems With PTS PAPR Reduction,” in IEEE Transactions on Vehicular
Technology, vol. 62, no. 1, pp. 444-449, Jan. 2013.

35. K. Singh, M. R. Bharti and S. Jamwal, “A modified PAPR reduction scheme
based on SLM and PTS techniques,” 2012 IEEE International Conference on
Signal Processing, Computing and Control, Waknaghat Solan, 2012, pp. 1-6.
36. Siegl, Christian & F H Fischer, Robert. (2008). Tone Reservation for Peak-to-
Average Power Ratio Reduction in OFDM under Different Optimization
Constraints.
37. Eugen-Victor Cuteanu, Alexandru Isar,”PAPR Reduction of OFDM signals
using Active Constellation Extension and Tone Reservation Hybrid Scheme,”
AICT 2012 : The Eighth Advanced International Conference on
Telecommunications.pp.156-163.pp.49-52.

15
2
Design of Sliding Contact
and Rolling Bearings
–Dr. B. Ramesh1,*
Bearing
Bearing is a stationary machine element which supports rotating machine
element (known as journal). It permits relative motion between the contact
surfaces of the members, while carrying the load.
Functions of Bearing
• To eliminate friction - Friction induces problems of torque, heat, wear,
inefficiency and power loss.
• To radially support and align the shaft
• To carry & disperse loads
• To locate the shaft axially
Classification of Bearing
I. Classification depending upon direction of load to be supported:
(a) Radial Bearings: Load acts perpendicular to the direction of
motion of the moving element.
1, *
Professor and Dean-R&D, Industry 4.0, Department of Mechanical Engineering, J.J.
College of Engineering and Technology, Sowdambikaa Group of Institutions,
Tiruchirappalli-620 009, Tamil Nadu, India.
Email id: rameshphd2010@yahoo.in

(b)Thrust Bearings: Load acts along the axis rotation.
II. Classification depending on nature of contact:
(a) Sliding Contact Bearing (or Plain Bearing): The sliding takes place
along the surfaces of contact between the moving element the fixed
element.

17
(b) Rolling Contact Bearings (or Anti-friction Bearing): Due to less
contact area rolling friction is much lesserthan the sliding friction,
hence these bearings are also known as antifriction bearing.
Journal or Sleeve or Sliding Contact bearing
A sliding contact bearing gives lateral support to rotating shaft. Load is
transferred through a lubricant in sliding contact. In sliding contact bearings,
the slidingtakes place along the surfaces of contact between the moving element
and the fixed element. A sliding contact bearing that supports a load in a radial
direction is known as Journal Bearing. It consists of two main parts, a shaft
and a hollow cylinder. The portion of the shaft inside the hollow cylinder also
known as Bearing is called as Journal. In most applications the journal rotates
while the bearing is stationary. However there are some applications where
the journal is stationary and the bearing rotates and even somewhere both the
journal and bearing rotates. The sliding contact bearings are also known as
Plain Bearings. Applications: turbines, large diesel engines etc
Types of Sliding Contact (or Journal or Sleeve) Bearing
The sliding contact bearings in which the sliding action is guided in a
straight line and carrying radial loads may be called slipper or guide bearings.
Such type of bearings are usually found in cross-head of steam engines. The
sliding contact bearings in which the sliding action is along the circumference
of a circle or an arc of a circle and carrying radial loads are known as journal or
sleeve bearings. When the angle of contact of the bearing with the journal is
360° then the bearing is called a full journal bearing. This type of bearing is
commonly used in industrial machinery to accommodate bearing loads in any
radial direction.
When the angle of contact of the bearing with the journal is 120°, then the
bearing is said to be partial journal bearing. This type of bearing has less friction
than full journal bearing, but it can be used only where the load is always in
one direction. The most common application of the partial journal bearings is
found in rail road car axles.
Design of Sliding Contact and Rolling Bearings

The full and partial journal bearings may be called as clearance bearings
because the diameter of the journal is less than that of bearing. When a partial
journal bearing has no clearance i.e. the diameters of the journal and bearing
are equal, then the bearing is called a fitted bearing. There are two types of
thrust bearings which take axial load, namely ‘footstep’ bearing and ‘collar’
bearing. The footstep bearing or simply ‘step’ bearing is a thrust bearing in
which the end of the shaft is in contact with the bearing surface. The collar
bearing is a thrust bearing in which a collar integral with the shaft is in contact
with the bearing surface. In this case, the shaft continues through the bearing.
The shaft can be with single collar or can be with multiple collars.
Lubrication
Lubrication is the science of reducing friction by application of a suitable
substance called lubricant, between the rubbing surfaces of bodies having
relative motion.
The objectives of lubrication are as follows:
1. to reduce friction
2. to reduce or prevent wear
3. to carry away heat generated due to friction
4. to protect the journal and the bearing from corrosion
The sliding contact bearings, according to the thickness of layer of the
lubricant between the bearingand the journal, may also beclassified as follows:
1. Thick film bearings: The thick film bearings are those in which the
working surfaces are completely separated from each other by the
lubricant. Such type of bearings are also called as hydrodynamic
lubricated bearings. Hydrodynamic lubrication is defined as a system
of lubrication in which the load-supporting fluid film is created by
the shape and relative motion of the sliding surfaces.
2. Thin film bearings: The thin film bearings are those in which, although
lubricant is present, the working surfaces partially contact each other
at least part of the time. Such typeof bearings are also called boundary
lubricated bearings.
3. Zero film bearings: The zero film bearings are those which operate
without any lubricant present.
4. Hydrostatic or externally pressurized lubricated bearings: The
hydrostatic bearings are those which can support steady loads without
any relative motion between the journal and the bearing. This is
achieved byforcingexternallypressurizedlubricantbetweenthemembers.
Hydrodynamic Lubrication
Initially, the shaft is at rest and it sinks to the bottom of the clearance
space under the action of load W. The surfaces of the journal and bearingtouch

19
during ‘rest’. As the journal starts to rotate, it climbs the bearing surface and as
the speed is further increased, it forces the fluid into the wedge-shaped region.
Since more and more fluid is forced into the wedge-shaped clearance space,
pressure is generated within the system. Since the pressure is created within
the system due to rotation of the shaft, this type of bearing is known as self-
acting bearing. The pressure generated in the clearance space supports the
external load (W). In this case, it is not necessary to supply the lubricant under
pressure and the only requirement is sufficient and continuous supply of the
lubricant. This mode of lubrication is seen in bearings mounted on engines
and centrifugal pumps. Most of the bearings used in industrial applications
are full journal bearings.
Hydrostatic lubrication
Hydrostatic lubrication is defined as a system of lubrication in which the
load supportingfluid film, separatingthe two surfaces is created by an external
source, like a pump, supplying sufficient fluid under pressure. Since the
lubricant is supplied under pressure, this type of bearing is called externally
pressurised bearing. The principle of hydrostatic lubrication in journal bearing
is as follows. Initially, the shaft rests on the bearing surface. As the pump starts,
high pressure fluid is admitted in the clearance space, forcing the surfaces of
the bearing and journal to separate out. Hydrostatic bearings are used on
vertical turbo generators, centrifuges and ball mills. Compared with hydrostatic
bearings, hydrodynamic bearings are simple in construction, easy to maintain
and lower in initial as well as maintenance cost.
Hydrostatic bearings, although costly, offer the following advantages:
(i) high load carrying capacity even at low speeds
(ii) no starting friction and
(iii) no rubbing action at any operating speed or load.
Materials used for Sliding Contact Bearings
1. Babbit metal
– Tin base babbits : Tin 90% ; Copper 4.5% ; Antimony 5% ; Lead
0.5%.
– Lead base babbits : Lead 84% ; Tin 6% ; Antimony 9.5% ; Copper
0.5%.
2. Bronzes
– gun metal (Copper 88% ; Tin 10% ; Zinc 2%)
– The phosphor bronze (Copper 80%; Tin 10%; Lead 9%;
Phosphorous 1%)
3. Cast iron
4. Silver

5. Non-metallic bearings
– carbon-graphite bearings
– soft rubber bearings
– wood bearings
6. Nylon and Teflon
Properties of Sliding Contact Bearing Materials
When the journal and the bearings arehaving proper lubrication i.e. there
is a film of clean, non-corrosive lubricant in between, separatingthe two surfaces
in contact, the only requirement of the bearing material is that they should
have sufficient strength and rigidity. However, the conditions under which
bearings must operate in service are generally far from ideal and thus the other
properties as below must be considered in selecting the best material.
1. Compressive strength: The bearing material should have high
compressive strength to withstand this maximum pressure so as to
prevent extrusion or other permanent deformation of the bearing.
2. Fatigue strength: The bearing material should have sufficient fatigue
strength so that it can withstand repeated loads without developing
surface fatigue cracks. It is of major importance in aircraft and
automotive engines.
3. Comformability: It is the ability of the bearing material to
accommodate shaft deflections and bearing inaccuracies by plastic
deformation (or creep) without excessive wear and heating.
4. Embeddability: It is the ability of bearing material to accommodate
(or embed) small particles of dust, grit etc., without scoring the material
of the journal.
5. Bondability: Many high capacity bearings are made by bonding one
or more thin layers of a bearing material to a high strength steel shell.
Thus, the strength of the bond i.e. bondability is an important
consideration in selecting bearing material.
6. Corrosion resistance: The bearing material should not corrode away
under the action of lubricating oil. This property is of particular
importance in internal combustion engines where the same oil is used
to lubricate the cylinder walls and bearings. In the cylinder, the
lubricating oil comes into contact with hot cylinder walls and may
oxidise and collect carbon deposits from the walls.
7. Thermal conductivity: The bearing material should be of high thermal
conductivity so as to permit the rapid removal of the heat generated
by friction.
8. Thermal expansion: The bearing material should be of low coefficient
of thermal expansion, so that when the bearing operates over a wide
range of temperature, there is no undue change in the clearance.

21
The various materials are used in practice, depending upon the
requirement of the actual service conditions. The choice of material for any
application must represent a compromise.
Lubricants used for Sliding Contact Bearings
The lubricants are used in bearings to reduce friction between the rubbing
surfaces and to carry away the heat generated by friction. It also protects the
bearing against corrosion.
All lubricants are classified into the following three groups:
(i) Liquid lubricants like mineral or vegetable oils
(ii) Semi-solid lubricants like grease
(iii) Solid lubricants like graphite or molybdenum disulphide
The liquid lubricants usually used in bearings are mineral oils and
synthetic oils. The mineral oils are most commonly used because of their
cheapness and stability. The liquid lubricants are usually preferred where they
may be retained. A grease is a semi-liquid lubricant having higher viscosity
than oils. The greases are employed where slow speed and heavy pressure
exist and where oil drip from the bearing is undesirable.
The solid lubricants are useful in reducing friction where oil films cannot
be maintained because of pressures or temperatures. They should be softer
than materials being lubricated. A graphite is the most common of the solid
lubricants either alone or mixed with oil or grease.
Properties of lubricants
1. Viscosity : It is the measure of degree of fluidity of a liquid. It is a
physical property by virtue of which an oil is able to form, retain and
offerresistance to shearing a buffer film-under heat and pressure. The
greater the heat and pressure, the greater viscosity is required of a
lubricant to prevent thinning and squeezing out of the film. The
variation of absolute viscosity with temperature for commonly used
lubricating oils is shown in PSGDB 7.41.
2. Oiliness : It is a joint property of the lubricant and the bearing surfaces
in contact. It is a measure of the lubricating qualities under boundary
conditions where base metal to metal is prevented only by absorbed
film. There is no absolute measure of oiliness.
3. Density: This propertyhas no relation to lubricating value but is useful
in changing the kinematic viscosity to absolute viscosity.
Mathematically
Absolute viscosity = × Kinematic viscosity (in m2
/s)
where
 = Density of the lubricating oil

4. Viscosity index: The term viscosity index is used to denote the degree
of variation of viscosity with temperature.
5. Flash point : It is the lowest temperature at which an oil gives off
sufficient vapour to support a momentary flash without actually
setting fire to the oil when a flame is brought within 6 mm at the
surface of the oil.
6. Fire point : It is the temperature at which an oil gives off sufficient
vapour to burn it continuously when ignited.
7. Pour point or freezing point: It is the temperature at which an oil will
cease to flow when cooled.
Terms used in Hydrodynamic Journal Bearing
Let D1
= Diameter of the bearing, D = Diameter of the journal, L= Length
of the bearing, O = centre of the journal and O2 = centre of the bearing.
The following terms used in hydrodynamic journal bearing are important
from the subject point of view:
1. Diametral clearance: It the difference between the diameters of the
bearing and the journal. Mathematically, diametral clearance, C = D1
– D. A commonly used clearance in industrial machines is 0.025 mm
per cm of journal diameter.
2. Radial clearance: It is the difference between the radii of the bearing
and the journal. Mathematically, radial clearance,
c = R1
– R =
1
2
D D
c

 =
2
C
3. Diametral clearance ratio: It is the ratio of the diametral clearance to
the diameter of the journal. Mathematically, diametral clearance ratio,
=
C
D
=
1
D D
D

4. Eccentricity: It is the radial distance between the centre (O) of the
bearing and the displaced centre (O2 ) of the bearing under load. It is
denoted by e.
5. Minimum oil film thickness: It is the minimum distance between the
bearing and the journal, under complete lubrication condition. It is
denoted by h0
and occurs at the line of centres. Its value may be
assumed as c / 4.
6. Attitude or eccentricity ratio: It is the ratio of the eccentricity to the
radial clearance. Mathematically, attitude or eccentricity ratio,
=
e
c
=
o
c h
c

= 1 –
o
h
c
= 1 –
2 o
h
C

23
7. Short and long bearing: If the ratio of the length to the diameter of the
journal (i.e. L/D) is less than 1, then the bearing is said to be short
bearing. On the other hand, if L/D is greater than 1, then the bearing
is known as long bearing. When the length of the journal (L) is equal
to the diameter of the journal (D), then the bearing is called square
bearing.
Bearing Characteristic Number and Bearing Modulus for Journal
Bearings
The coefficient of friction in design of bearings is of great importance,
because it affords a means for determining the loss of power due to bearing
friction. It has been shown by experiments that the coefficient of friction for a
full lubricated journal bearing is a function of three variables, i.e.
( ) ( ) ( )
Zn D L
i ii iii
P C D
Therefore, the coefficient of friction may be expressed as,
 = [(Zn/P),(D/C), (L/D)]
where
 = Coefficient of friction,
Ö = A functional relationship,
Z = Absolute viscosity of the lubricant, in kg/m-s,
n = Speed of the journal in rpm,
P = Bearing pressure on the projected bearing area in N/mm2
,
= Load on the journal W÷ (L × D)
D = Diameter of the journal in mm,
L = Length of the bearing in mm, and
C = Diametral clearance in mm.
The factor (Zn/P) is termed as bearing characteristic number and is a
dimensionless number. The variation of coefficient of friction with the operating
values of bearing characteristic number (Zn/P) has been obtained by McKee
brothers (S.A. McKee and T.R. McKee) in an actual test of friction. The factor
(Zn/P) helps to predict the performance of a bearing.
Coefficient of Friction for Journal Bearings (PSGDB 7.34)
To determine the coefficient of friction for well lubricated full journal
bearings, the following empirical relation established by McKee based on the
experimental data:
Coefficient of friction,
 = 8
33.25
10
Zn D
k
P C
  

  
  

Or
 = 10
3325
10
Zn D
k
P C
  

  
  
Where
k = Factor to correct for end leakage. It depends upon the ratio L/D.
= 0.002 for L/D ratios of 0.75 to 2.8. (PSGDB 7.34)
Mckee’s equation may be rewritten as:
 = 0.326
Zn D
k
P C
  

  
  
Where,
 = Coefficient of friction
Z = Absolute viscosity of the lubricant, in kg / m-s,
n = Speed of the journal in rpm;
P = Bearing pressure on the projected bearing area in N/m2
= Load on the journal (W÷ (L × D))/*106
N/m2
D = Diameter of the journal, mm
L = Length of the bearing, mm and
C = Diametral clearance, mm.
To determine the coefficient of friction for well lubricated full journal
bearings, the following relation established by Petroff based on the experimental
data also can be used
Coefficient of friction,
 =
2
2
Zn D
P C


  
  
  
Petroff’s equation indicates that there are two important dimensionless
parameters, namely, (D/C) and (Zn’/P) that govern the coefficient of friction
and other frictional properties like frictional torque, frictional power loss and
temperature rise in the bearing
Design of Journal Bearing
Critical Pressure of the Journal bearing
The pressure at which the oil film breaks down so that the metal to metal
contact begins, is known as critical pressure orthe minimum operating pressure
of the bearing. It may be obtained by the following relation.
P =
2
2
6
/
4.75 10
ZN D l
N mm
C d l
   
   
 
   

25
Sommerfeld number
In the design of fluid bearings, the Sommerfeld number (S), or bearing
characteristic number, is a dimensionless quantity used extensively in
hydrodynamic lubrication analysis. The Sommerfeld number is very important
in lubrication analysis because it contains all the variables normally specified
by the designer (PSGDB 7.34). The Sommerfeld number is named after Arnold
Sommerfeld (1868–1951)
Sommerfeld number =
2
Zn D
P C
 
 
 
Where,
Z in kg/m-s, n’ in rps, P in N/m2
or 106
N/mm2
, D - journal diameter and
C- diametral clearance.
By referring a design data book, you can calculatethe Sommerfeld number
for a given L/D ratio. Using this number, you can calculate the viscosity of the
oil that is to be used in the bearing.
Heat Generated in a Journal Bearing
The heat generated in a bearing due to the fluid friction and friction of
the parts having relative motion (PSGDB 7.34),
Hg
=  W v Watts or Nm/s
Where, µ = Coefficient of friction, W = bearing load in N, v = surface velocity
of the journal in m/s
After the thermal equilibrium is reached, heat will be dissipated at the
outer surface of the bearing at the same rate at which it is generated in the oil
film. The amount of heat will depend upon the temperature difference size
and mass of the radiating surface and on the amount of air flowing around the
bearing. However for the convenience in bearing design the actual heat
dissipating area may be expressed in terms of the projected area of the journal.
Heat Dissipated by the Bearing
The heat dissipated in the bearing,
Hd
= Cd
A (tb
- ta
) Watts or N-m/s
Where,
Cd
= Combined coefficient of radiation and convention, W/m2
°C
= 140 - 420 W/m2
°C for unventilated bearing
= 490 - 1400 W/m2
°C for well ventilated bearing
A - projected area of the bearing = LD in m2
tb
-temperature of the bearing surface °C
ta
- temperature of the surrounding air °C

Also Lasche’s equation for heat dissipated of 360° bearing (PSGDB 7.34),
Hd
=
2
( 18)
t LD
K
 
Where
T = tb
– ta
=
( )
2
a a
t t

K = Constant (Divide the Data book value by 1600)
= 0.273 for bearing of heavy construction and well ventilated °Cm2
/W
= 0.484 for bearing of light or medium construction in still air, °Cm2
/W
Mass Flow Rate of Oil
If Hg
> Hd
, then the bearing is cooled by circulating water or oil through
coils built in the bearing using a pump and the mass of the oil required to
remove the heat generated can be obtained from the following equation
Hg
- Hd
= Mass flow rate ×specific heat of oil ×temperature rise in oil
Hg
– Hd
= mo
× 1710 J/kg °C × 6°C
Raimondi and Boyd Method
There is no exact solution to Reynold’s equation for a journal bearing
having a finite length. However, AA Raimondi and John Boyd of Westinghouse
Research Laboratory solved this equation on computer using the iteration
technique. The results of this work are available in the form of charts (PSGDB
7.40) and tables (PSGDB 7.36 to 7.39). In the Raimondi and Boyd method, the
performance of the bearing is expressed in terms of dimensionless parameters.
Table in PSGDB 7.36 gives values of these parameters for a full journal bearing
with side flow.
Operating Pressure
Minimum pressure or critical pressure of which oil film breaks down and
metal to metal contact begins.
2
6
4.75 10
Z n D L
p
C D L
    
    
 
   
Heat Generated due to Friction
Operating temperature – 50° to 80°C
µ - coefficient of friction

27
W – Load = p×L×D
L- length of bearing
D- diameter of bearing
v - rubbing velocity
60
D n
  
Heat Dissipating Capacity of Bearing
Hd
=
2
( 18)
t
L D
K
 
 
min
f
kg m

t – temperature rise of bearing surface from ambient temperature in °C
0
1
( )
2
a
t t t
  
to
– temperature of oil
ta
– ambient temperature
K – constant for heat dissipation
= 437 for heavy construction well ventilated
= 775 for light construction in still air
In SI units
Hd
=
2
( 18)
t
L D
K
 
  Watts
K – constant for heat dissipation
= 0.273 for heavy construction well ventilated
= 0.484 for light construction in still air
Rolling Contact Bearing
In rolling contact bearing, the contact between the bearing elements is
rolling instead of sliding. Since the contact between the bearing elements is
rolling, this type has very small friction and thus it is also called as antifriction
bearing. For starting conditions and at moderate speeds, the frictional losses
in rolling contact bearing are lower than that of equivalent hydrodynamic
journal bearing. This is because the sliding contact is replaced by rollingcontact
resulting in low coefficient of friction. Therefore, rolling contact bearings are
called ‘antifriction’ bearings.
However, this is a misnomer. There is always friction at the contacting
surfaces between the rolling element and the inner and outer cages. A rolling
contact bearing consists of four parts— inner and outer races, a rolling element

like ball, roller or needle and a cage which holds the rolling elements together
and spaces them evenly around the periphery of the shaft.
Basically the structure of ball bearings are similar except that whether
the rolling element between the inner ring and outer ring are balls or rollers.
Also these ball bearings are many types such as deep groove ball bearings,
angular contact ball bearings and so on. Both type of bearing can carry radial
loads and axial loads acted individually or in combined form.
Generally the ball bearings are used for light loads and the roller bearings
are usually used for heavier loads. Also in the case of ball bearings the nature
of contact is the point contact hence the friction produced is veryless compared
to roller bearings where the nature of contact is the line contact which produce
more friction.
Types of Rolling Contact Bearing
I. Based on the type of rolling contact
(a) Ball bearing
(b) Roller bearing
II. Based on the load to be carried
(a) Radial bearing: Radial bearings accommodate loads that are
predominantly perpendicular to the shaft.
(b) Thrust bearing: Thrust bearings accommodate loads that act
predominantly along the axis of the shaft.
Bearing Selection – Space
• Limited Radial Space
– Choose bearing with low cross-sectional height
– Eg. Needle roller and cage assemblies
• Limited Axial Space
– Choose bearings that can handle combined loads
– Eg. Cylindrical roller, deep groove, needle roller
Bearing Selection – Loads
• Magnitude
– Roller bearings support heavier loads than similar sized ball
bearings
– Full complement roller bearings support heavier loads than
corresponding caged bearings
• Radial
– Some cylindrical roller and all needle roller

29
• Axial
– Thrust ball bearing and four-point contact ball
– Angular contact thrust ball bearings
• Combined
– Greater the angle of contact, greater ability to handle axial loads
• Moment
– Eccentric loads resulting in tilting moment
– Best: paired single row angular contact bearings or tapered roller
bearings
Bearing Selection – Speed
• Highest Speeds
– Purely Radial Loads
• Deep Groove Ball Bearings
• Self Aligning Ball Bearings
– Combined Loads
• Angular Contact
Thrust bearings cannot accommodate high speeds as radial bearings.
Designation/Specification of Bearing
It consists of 5 digits. First digit – Type of bearing. Second digit – Width-
Height series. Last two digits – Bore of bearing (gives 1/5th
of bore).
Example: SKF6305
6 – Deep groove bearing
3 – Width-Height series
5 – 5 X 5= 25 mm bore
The last two digits indicate the bore diameter of the bearing in mm
(bore diameter divided by 5). For example, XX07 indicates a bearing of 35 mm
bore diameter. The third digit from the right indicates the series of the bearing.
The numbers used to indicate the series are as follows:
• Extra light series –1
• Light series – 2
• Medium series – 3
• Heavy series – 4
For example, X307 indicates a medium series bearing with a bore diameter
of 35 mm. The fourth digit and sometimes fifth digit from the right specifies
the type of rolling contact bearing. For example, the digit 6 indicates deep
groove ball bearings. Light series bearings permit smallest bearing width and
outer diameter for a given bore diameter. They have lowest load carrying
capacities. Medium series bearings have 30 to 40 per cent higher dynamic load

carrying capacities compared with light series bearings of the same bore
diameter. However, they occupy more radial and axial space. Heavy series
bearings have 20 to 30 per cent higher dynamic load carrying capacities
compared with medium series bearings of the same bore diameter.
Bearing Life
The life of an individual bearing is the number of revolutions (or hours at
some given constant speed) which the bearing runs before the first evidence of
fatigue develops in the material of either ring or in a ball. The rating life
(minimum life) of a group of apparently identical bearings is defined as the
number of revolutions (or hours at some given constant speed) that 90 per cent
of a group of bearings will complete or exceed before the first evidence of
fatigue develops.
Applications of Bearings
Sliding contact bearings are used in the following applications:
(i) crankshaft bearings in petrol and diesel engines
(ii) centrifugal pumps
(iii) large size electric motors
(iv) steam and gas turbines and
(v) concrete mixers, rope conveyors and marine installations.
Rolling contact bearings are used in the following applications:
(i) machine tool spindles
(ii) automobile front and rear axles
(iii) gear boxes
(iv) small size electric motors and
(v) rope sheaves, crane hooks and hoisting drums.
Advantages of Rolling Contact Bearings Over Journal Bearings
1. Friction, starting as well as running, is low except at high speeds
2. Shaft alignment can be made with greater accuracy
3. Heavy momentary overloads can be carried without failure
4. Lubrication is simple requiring very little attention
5. Some types of bearings can carry both radial and axial loads
6. Replacement is easy
7. Selection of bearings using manufacturer’s catalogue is relatively
simple
Disadvantages of Rolling Contact Bearings Over Journal Bearings
1) Cost of bearing and the necessary mounting is generally greater
2) Failure of bearing occurs suddenly without warning (fatigue failure)
3) Noisier in normal operation.

31
Principle of Self-aligning Bearing
In many applications, the bearing is required to tolerate a small amount
of misalignment between the axes of the shaft and the bearing. The
misalignment may be due to deflection of the shaft under load or due to
tolerances of individual components. Self-aligning bearings are used in these
applications. In self-aligning bearing, the external surface of the bearing bush
is made spherical. The centre of this spherical surface is at the centre of the
bearing. Therefore, the bush is free to roll in its seat and align itself with the
journal. Arrangement is made to provide lubricant between the spherical
surfaces of the bush and its seat in order to reduce the friction. This principle is
used in self-aligning ball bearings and spherical roller bearings. Self-aligning
bearings are commonly employed when accurate alignment is impossible or
unfeasible.
Selection of Rolling Contact Bearings
The data necessary for the selection of bearings are: Radial load, Thrust
load, Speed of shaft, Desired life of bearings in hours and Conditions of loading
(steady/impact etc.,)
The Basic Dynamic load capacity, C
C =
1
10
k
L
P
L
 

 
 
Where,
L - required life of bearing in million revolutions
L10
- 1 million revolutions (life of bearing for 90% survival)
k - exponent (3 for ball bearing, 10/3 for roller bearings)
P – Equivalent radial load
The static equivalent radial load may be defined as the static radial load
(in case of radial ball or roller bearings) or axial load (in case of thrust ball or
roller bearings) which, if applied, would cause the same total permanent
deformation at the most heavily stressed ball (or roller) and race contact as
that which occurs under the actual conditions of loading.
P = (V.X.Fr
+Y.Fa
).S (PSGDB 4.2)
Fr
- radial load, Fa
- axial load, V – Rotation factor (1 for inner race rotation,
1.2 for outer race rotation), X- radial load factor (PSGDB 4.4), Y- axial load
factor (PSGDB 4.4), S- service factor (PSGDB 4.2)
Important Definition of Rolling Contact Bearings
The size of bearing required is judged by the magnitude and nature of
applied load, life and reliability. The bearing load is composed of weights

involved forces derived from power transmitted and additional force based
on method of operation.
The Basic Static Load Rating (CO
)
It is defined as the static radial load (in case of radial ball or roller bearings)
or axial load (in case of thrust ball or roller bearings) which corresponds to a
total permanent deformation of the ball (or roller) and race, at the most heavily
stressed contact, equal to 0.0001 times the ball (or roller) diameter.
The Basic Dynamic Load Rating (C)
It is defined as the constant stationary radial load (in case of radial ball or
roller bearings) or constant axial load (in case of thrust ball or roller bearings)
which a group of apparently identical bearings with stationary outer ring can
endure for a rating life of one million revolutions (which is equivalent to 500
hours of operation at 33.3 r.p.m.) with only 10 per cent failure. (PSGDB 4.2).
Ball and roller bearings have finite service life and it is required to
determine the load corresponding to the desired service life. When a large
number of identical bearings are tested for the same load, the failure curve is
obtained as shown in the following figure. The relationship between bearing
life and reliability is given by a statistical curve known as Wiebull distribution.
Point A represents average life (NA
) of bearings of the entire group. Point
B represents 10% of the bearings tested have life (NB
) twice that of average.
Point C represents 90% of the bearings tested have life (NC
) about 1/5th
of that
of average. It represents that 90% of the bearings have a minimum life of N
cycles, which is known as rating life (L10
– life or minimum life). The load that
a given type and size of bearing can carry for 106
revolution with 10% failures
is called the basic dynamic load rating. Some manufacturers specify the load
rating on the basis of a certain speed and a certain L10
life or an average life. It
has been found experimentally that two groups of identical bearings tested

33
under different loads P1
and P2
will have respective lives L1
and L2
according
to the relation,
1 2
2 1
k
L P
L P
 
  
 
Where
k = 3 for ball bearings and 10/3 for roller bearings
Using the above equation,knowing the value of C for1 million revolutions
from the catalogue, the rating life of the bearing subjected to any other load P
can be calculated.
Selection of Bearings
1. Based on the diameter of the shaft and the type of bearing, select
tentatively bearing with number from the manufacturers catalogue.
(PSGDB 4.12 to 4.36)
2. Calculate the value of (Fa
/C0
)
3. Find the value of ‘e‘ proportional to (Fa
/C0
) from the table PSGDB 4.4
for the required type of bearing.
4. Calculate (Fa
/Fr
) and check
5. Consulting the table (PSGDB 4.4) for the value of ‘e’ obtains the values
of X and Y by interpolation.
6. Calculate the Equivalent load P =(XFr
+ YFa
).S (PSGDB 4.2).
7. Calculate the dynamic load rating
C =
1
10
k
L
P
L
 

 
 
8. Check the calculated value of C with the catalogue value in the tables.
9. If calculated C < Table [C] value, then the selection is safe. If not, select
next series of bearing and check again the above steps.
a
r
F
e
F
 or
a
r
F
e
F

Selection of Bearing for Variable Loading
The rolling contact bearing frequently operate under variable load and
speed conditions. This is due to many causes like power fluctuation in electrical
machineries or requirement of different cutting forces for different kinds of
machining tools, or running with loading and unloading condition as in
automobiles. Such as variable loaded bearings are designed by considering all
these different loaded conditions of workcycle and not solely upon most severe

operating conditions. The work cycle may be divided into a number of portions
in each of which operation condition may be taken as constant.
Fm
=
1/3
3 3 3
1 1 2 2 3 3....
F n F n F n
n
 
 
 

 
For variable speed, the cubic mean load (revolutions varying) PSGDB 4.2
Fm
=
1/3
3 3 3
1 1 2 2 3 3....
F t F t F t
t
 
 
 

 
For variable time, the cubic mean load (time varying) PSGDB 4.2
F1
- constant load during n1
revolution (or) during the period of time t1
F2
- constant load during n2
revolution (or) during the period of time t2
and so on.
n = n1
+n2
+n3
+…+nn
(Or) t = t1
+t2
+t3
+…+tn
Bearing with a probability of survival other than 90% :
In the definition of rating life, it is mentioned that the rating life is the life
that 90% of a group of identical bearings will complete or exceed before fatigue
failure. The reliability ‘p’ is defined as,
p =
No.of bearings which havesuccessfully
completedLmillion revolutions
Totalnumber of bearingsunder test
Therefore, the reliability of bearings selected from the manufacturer’s
catalogue is 0.9 or 90%. In certain applications, where there is risk to human
life, it becomes necessary to select a bearing having a reliability of more than
90%. The bearings selected from tables have 10% failures or 90% survival or
The reliability of any one bearings 0.9 or 90%. In a system, if there are a number
of bearings, the individual reliability of each bearing should be fairly high.
If there are N bearings in the system, each having the same reliability R
then the reliabilityof the complete system is given by,ps
= (p)N
where ps
indicates
the probability of one out of N bearings failing during its lifetime. If a machine
is assemble with six such bearings, the reliability of all the bearings in the
assembly is R6
= (0.9)6
= 0.531. Thus the reliability of the entire assembly is
much reduced. Hence there is a need to select bearings having reliabilities
greater than 90% and for which the following formula can be used.
 
 
1/
10 10
ln 1/
ln 1/
b
p
L
L p
 
  
 
 

35
Where,
L = required life of bearing in million revolutions with probability of
survival p, L10
’= calculated life of selected bearing for the given load, for 90%
survival, p = probability of survival, p10
= 0.9 and the value of b = 1.17 for a
median life = 5 L10
. Equation is used for selecting the bearing when the reliability
is other than 90%.
Rolling Contact Bearing Failure – Causes & Remedies
There are two basic types of bearing failure— breakage of parts like races
or cage and the surface destruction. The fracture in the outer race of the ball
bearing occurs due to overload. When the bearing is misaligned, the load acting
on some balls or rollers sharplyincreases and may even crush them. The failure
of the cage is caused due to the centrifugal force actingon the balls. The complete
breakage of the parts of the ball bearing can be avoided by selecting the correct
ball bearing, adjusting the alignment between the axes of the shaft and the
housing and operating within permissible speeds. In general, the failure of
antifriction bearing occurs not due to breakage of parts but due to damage of
working surfaces of their parts.
The principal types of surface wear are as follows:
Abrasive wear
Abrasive wear occurs when the bearing is made to operate in an
environment contaminated with dust, foreign particles, rust or spatter.
Remedies against this type of wear are provision of oil seals, increasing surface
hardness and use of high viscosity oils. The thick lubricating film developed
by these oils allows fine particles to pass without scratching.
Corrosive wear
The corrosion of the surfaces of bearing parts is caused by the entry of
water or moisture in the bearing. It is also caused due to corrosive elements
present in the Extreme Pressure (EP) additives that are added in the lubricating
oils. These elements attack the surfaces of the bearing, resulting in fine wear
uniformly distributed over the entire surface. Remedies against this type of
wear are, providing complete enclosure for the bearing free from external
contamination, selecting proper additives and replacing the lubricating oil at
regular intervals.
Pitting
Pitting is the main cause of the failure of antifriction bearings. Pitting is a
surface fatigue failure which occurs when the load on the bearing part exceeds
the surface endurance strength of the material. This type of failure is

characterized by pits, which continue to grow resultingin complete destruction
of the bearing surfaces. Pitting depends upon the magnitude of Hertz’ contact
stress and the number of stress cycles. The surface endurance strength can be
improved by increasing the surface hardness.
Scoring
Excessive surface pressure, high surface speed and inadequate supply of
lubricant result in breakdown of the lubricant film. This results in excessive
frictional heat and overheating at the contacting surfaces. Scoring is a stick-
slip phenomenon, in which alternate welding and shearing takes place rapidly
at high spots. Here, the rate of wear is faster. Scoringcan be avoided by selecting
the parameters, such as surface speed, surface pressureand the flow of lubricant
in such a way that the resulting temperature at the contacting surfaces is within
permissible limits.
REFERENCES
1. Joseph Shigley, Charles Mischke, Richard Budynas and Keith Nisbett
“Mechanical Engineering Design”, 8th
Edition, Tata McGraw-Hill, 2008.
2. Bhandari.V.B. “Design of Machine elements”, (2010) Tata Mc Graw Hill Book
Co, Third Edition.
3. R.S.Khurmi, J.K.Gupta. “Machine Design”, (2008) Eurasia Publishing House
(Pvt.) Ltd. Revised Edition.
4. C.S.Sharma, KamleshPurohit, “Design of Machine Elements”, Prentice Hall
of India, Pvt. Ltd., 2003.
5. Bernard Hamrock, Steven Schmid, Bo Jacobson, “Fundamentals of Machine
Elements”, 2nd
Edition, Tata McGraw-Hill Book Co., 2006.
6. Robert C. Juvinall and Kurt M. Marshek, “Fundamentals of Machine Design”,
4th
Edition, Wiley, 2005.
7. Alfred Hall, Halowenko, A and Laughlin, H., “Machine Design”, Tata
McGraw-Hill BookCo.(Schaum’s Outline), 2010.
8. Merhyle F. Spotts, Terry E. Shoup and Lee E. Hornberger, “Designof Machine
Elements” 8th
Edition, Printice Hall, 2003.
9. Sundararajamoorthy T. V, Shanmugam N, “Machine Design”, Anuradha
Publications, Chennai, 2003.

37
3
Design of Keys, Couplings and Joints
–Dr. B. Ramesh1,*
Keys
A key can be defined as a machine element which is used to connect the
transmission shaft to rotating machine elements like pulleys, gears, sprockets
or flywheels. A keyed joint consisting of shaft, hub and key is illustrated in the
following Figure.
A recess or slot machined either on the shaft orin the hub to accommodate
the key is called keyway. The keyway is usually cut by a vertical or horizontal
milling cutter, which results in stress concentration in the shaft and the part
becomes weak. This is the main drawback of a keyed joint.
Key Materials
Keys are made of plain carbon steels like 45C8 or 50C8 in order to
withstandshear and compressive stresses resultingfrom transmission of torque.
According to Indian standards, steel of tensile strength not less than 600 N/
mm2
shall be used as the material for the key.
1,*
Professor and Dean-R&D,Industry 4.0, Department ofMechanical Engineering, J.J. College
of Engineering and Technology, Sowdambikaa Group of Institutions, Tiruchirappalli-
620 009, Tamil Nadu, India.
Email id: rameshphd2010@yahoo.in

Basic Functions of the Key
1. The primary function of the key is to transmit the torque from the
shaft to the hub of the mating element and vice versa.
2. The second function of the key is to prevent relative rotational motion
between the shaft and the joined machine element like gear or pulley.
In most of the cases, the key also prevents axial motion between two
elements, except in case of feather key or splined connection.
Classification of keys
1. Saddle key and sunk key
2. Square key and flat key
3. Taper key and parallel key
4. Key with and without Gib-head
In addition, there arespecial types of keys such as Woodruff key, Kennedy
key or feather key. The selection of the type of key for a given application
depends upon the following factors: power to be transmitted, tightness of fit,
stability of connection, and cost.
Saddle Keys
A saddle key is a key which fits in the keyway of the hub only. In this
case, there is no keywayon the shaft. Thereare two types of saddle keys, namely,
hollow and flat, as shown in the following Figure. In both types of saddle keys,
friction between the shaft, key and hub prevents relative motion between the
shaft and the hub. The power is transmitted by means of friction and are suitable
for light duty or low power transmission.
Sunk keys
A sunk key is a key in which half the thickness of the key fits into the
keywayon the shaft and the remaininghalf in the keywayon the hub. Therefore,
keyways are required both on the shaft as well as the hub of the mating element.

39
This is a standard form of key and may be either of rectangular or square
cross-section. In sunk key, power is transmitted due to shear resistance of the
key. The relative motion between the shaft and the hub is also prevented by
the shear resistance of key. Therefore, sunk key is suitable for heavy duty
application. It is a positive drive, which is the main advantage of the sunk key
over the saddle key. It is necessary to cut keyways both on the shaft and the
hub. Therefore, the cost of the sunk key joint is more than that of the saddle
key joint. The industrial practice is to use a square key with sides equal to one-
quarter of the shaft diameter and length at least 1.5 times the shaft diameter.
b = h =
4
d
I = 1.5 d
Where,
b = width of key (mm), h = height or thickness of key (mm), l = length of
key (mm), d = diameter of shaft (mm)
For a flat key, the thumb-rule dimensions are as follows:
b =
4
d
h =
2
3
b =
6
d
I = 1.5 d
The standard dimensions of square and rectangular cross-section sunk
keys are given in Table PSGDB 5.16. Sunk keys are classified into two groups,
namely, parallel and taper keys. A parallel key is a sunk key which is uniform
in width as well as height throughout the length of the key. A taper key is
uniform in width but tapered in height. The standard taper is 1 in 100. The
bottom surface of the key is straight and the top surface is given a taper.
The taper is provided for the following two reasons:
1. When the key is inserted in the keyways of shaft and the hub and
pressed by means of hammer, it becomes tight due to wedge action,
which insures tightness of joint in operating conditions and prevents
loosening of the parts.
2. Due to taper, it is easy to remove the key and dismantle the joint.
Gib Head Keys
A gib head key is similar to a square or rectangular key but it has a head
at one end; generally at the larger end of the taper sunk key. The gib head is
used for driving the key while assembling or disassembling. The projection of
Gib-head is hazardous in rotating parts.
Feather Key
A feather key is a parallel key which is fixed either to the shaft or to the
hub and which permits relative axial movement between them. Feather key is
used where it is necessary to slide a keyed gear; pulley assembly along the
shaft. Keys are tight fitted or screwed on the shaft.

Woodruff Key
A Woodruff key is a sunk key in the form of an almost semicircular disk
of uniform thickness. The keyway in the shaft is in the form of a semicircular
recess with the same curvature as that of the key. Once placed in position, the
Woodruff key tilts and aligns itself on the shaft. Woodruff keys are used on
tapered shafts in machine tools and automobiles.
The advantages of Woodruff key are as follows:
1. The Woodruff key can be used on tapered shaft because it can align
by slight rotation in the seat.
2. The extra depth of key in the shaft prevents its tendency to slip over
the shaft.
The disadvantages of Woodruff key are as follows:
1. The extra depth of keyway in the shaft increase stress concentration
and reduces its strength.
2. The key does not permit axial movement between the shaft and the
hub.
Round Keys
The round keys are circular in section and fit into holes drilled partly in
the shaft and partly in the hub. They have the advantage that their keyways
may be drilled and reamed after the mating parts have been assembled. Round
keys are usually considered to be most appropriate for low power drives.
Sometimes the tapered pin is held in place by the friction between the pin and
the reamed tapered holes.
Forces Acting on a Sunk Key
Forces due to tight fit of the key and thus compressive stress is induced
(Neglected). Force due to torque transmitted by the shaft and this force
produced shearing and crushing stresses in the key. The induced shearing and
crushing stresses may be checked.
Considering shearing of the key:
The torque transmitted,
. .
( )
2
t k
b l d
M 

Considering crushing of the key:
The torque transmitted,
. .
( )
2
t C
h l d
M 


41
Where,
b = width of the key; h = thickness of key; l = length of the key; [k
] =
Allowable or design shear stress of the key material; [óc
]= Allowable or design
crushing stress induced in the key material.
If [c
] value not given then take [c
]= [t
].
Kennedy Key
The Kennedy key consists of two square keys. In this case, the hub is
bored off the centre and the two keys force the hub and the shaft to a concentric
position. Kennedy key is used for heavy duty applications. The analysis of the
Kennedy key is similar to that of the fl at key.
Considering shearing of the key:
2
t
M
dbl
 
Considering crushing of the key:
2 t
c
M
dbl
 
Splines
Sometimes, keys are made integral with the shaft which fits in the keyways
broached in the hub. Such shafts are known as splined shafts. These shafts
usually have four, six, ten or sixteen splines. The splined shafts are relatively
stronger than shafts having a single keyway. The splined shafts are used when
the force to be transmitted is large in proportion to the size of the shaft as in
automobile transmission and sliding gear transmissions.
By using splined shafts, axial movements as well as positive drive are
obtained.
Let:
D = major diameter of splines (mm)
d = minor diameter of splines (mm)
l = length of hub (mm)
n = number of splines
Mt
= transmitted torque (N-mm)
pm
= permissible pressure on spline (N/mm2
)
A = total area of splines (mm2
)
A =
1
( )
2
D d l n
  
Rm
= mean radius of splines (mm)

Rm
=
( )
4
D d

The torque transmitting capacity of splines is given by:
Mt
=
2 2
1
(D )
8
m m m
p AR p l n d
     
The permissible pressure on the splines is limited to 6.5 N/mm2
.
Effect of Keyways
The keyway cut into the shaft reduces the load carrying capacity of the
shaft. This is due to the stress concentration near the corners of the keyway
and reduction in the cross sectional area of the shaft. The torsional strength of
shaft is reduced. The following relation for the weakening effect of the keyway
is based on the experimental results by H.F. Moore.
1 . 1.1
b t
e o z
d d
   
  
   
   
Where,
e = Shaft strength factor. It is the ratio of the strength of the shaft with
keyway to the strength of the same shaft without keyway
b = Width of keyway
h = Thickness of key
d = Diameter of shaft and
t = Depth of keyway = (h / 2)
Couplings
A coupling can be defined as a mechanical device that permanently joins
two rotating shafts to each other. The most common application of coupling is
joiningof shafts of twoseparately built or purchased units so that a newmachine
can be formed.
For example,
• A coupling is used to join the output shaft of an engine to the input
shaft of a hydraulic pump to raise water from well.
• A coupling is used to join the output shaft of an electric motor to the
input shaft of a gearbox in machine tools.
• A coupling is also used to join the output shaft of an electric motor to
the input shaft of a compressor.
Coupling is a permanent connection, while the clutch can connect or
disconnect two shafts at the will of the operator.
Shaft couplings are used in machinery for several purposes:

43
• To provide for connection of shaft of units those are manufactured
separately.
• To provide for misalignment of the shaft or to introduce mechanical
flexibility.
• To reduce the transmission of shock loads from one shaft to another.
• To introduce protection against over loads.
Requirement of a Good Shaft Coupling
1. It should be easy to connect or disconnect.
2. It should transmit the full power from one shaft to the other shaft
without losses.
3. It should hold the shaft in perfect alignment.
4. It should have no projecting parts.
Types of Shaft Couplings
1. Rigid coupling: It is used to connect two shafts which are perfectly
aligned. The types are
• Sleeve (or) muff coupling
• Clamp (or) split muff (or) compression coupling
• Flange coupling
2. Flexible coupling: It is used to connect two shafts having lateral and
angular misalignments. The types are
• Bushed pin type coupling
• Universal coupling
• Oldham coupling
Sleeve (or) Muff Coupling (PSGDB 7.133)
It is made of cast iron. It consists of a hollow cylinder whose inner diameter
is that same as that of the shaft. It is fitted over the ends of two shafts by means
of a gib head key. The power transmitted from one shaft to other shafts by
means of a key and a sleeve.
• Outer diameter of sleeve D=2d+13mm
• Length of sleeve L=3.5d
• d- diameter of shaft

Design of Muff Coupilng (PSGDB 7.133)
1. Calculate the diameter of each shaft: Using the following equations
find out the diameter of the shaft and round it to R20 series
60
1000
2
t
p
M N mm
N


  
3
16
[ ] t
M
d



2. Design for sleeve : Sleeve outer diameter D = (2d + 13) mm and
L = 3.5 d
Also, check the torsional shear stress induced in the sleeve by the
following equations:
The sleeve is designed by considering it as a hollow shaft
4 4
16
t c
D d
M
D


 

   
 
3. Design for key : Based on the diameter of the shaft, select the key
dimensions from PSGDB 5.16. The length of coupling key is at least
equal to the length of the sleeve. The coupling key is usually made
into two parts so that the length of key in each shafts; l= L/2=(3.5 d)/2
After that the induced shearing and crushing stresses may be checked.
The torque transmitted :
Considering shearing of the key,
. .
[ ]
2
t k
b l d
M 

Considering crushing of the key,
. .
[ ]
4
t c
hl d
M 

Split Muff (or) Clamp (or) Compression Coupling
The clamp coupling is also called compression coupling or split muff
coupling. It is a rigid type of coupling. In this case the muff or sleeve is made
into two halves are bolted together. The halves of the muff are made of cast
iron. The shaft end is made to abut each other and a single key is fitted directly
in the keyway of both the shaft. Both the halves are held together by means of
mild steel bolts and nuts. The number of bolt may be two or four or six.
The usual proportions of themuff forthe clamporcompressioncouplingare:
• Diameter of muff D=2d+13mm
• Length of muff or sleeve L=3.5d

45
A small clearance is provided in the parting plane between the two halves.
The torque is transmitted by means of frictional force on the surface of the
shaft. There is also a key between the shafts and sleeve, which also transmits
torque.
Design of Clamp (or) Compression Coupling
1. Calculate the diameter of each shaft: Using the following equations
find out the diameter of the shaft and round it to R20 series
60
1000
2
t
p
M N mm
N


  
3
16
[ ] t
M
d



2. Design for sleeve: Sleeve outer diameter D = (2d + 13) mm and
L = 3.5 d
Also, check the torsional shear stress induced in the sleeve by the
following equations: The sleeve is designed by considering it as a
hollow shaft.
4 4
16
t c
D d
M
D


 

   
 
3. Design for key: Based on the diameter of the shaft, select the key
dimensions from PSGDB 5.16. The length of coupling key is at least
equal to the length of the sleeve. The coupling key is usually made
into two parts so that the length of key in each shaft l = L/2. After that
the induced shearing and crushing stresses may be checked.
Considering shearing of the key,
. .
[ ]
2
t k
b l d
M 

Considering crushing of the key,
. .
[ ]
4
t c
hl d
M 

4. Design of clamping bolts: Torque transmitted by the coupling,
2
2
( )
16
t t b
M d n d

 
     
Where
Mt
- torque transmitted by the shaft
d - diameter of shaft
db
- root or effective diameter of bolt

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