a study conducted in the topic of crack propagation and life expectancy, falling under the spectrum of fracture mechanics. the study also includes a correlational example of crack on a railway track.

1. Project report
on
A Study on
Crack Propagation and Life expectancy.
PRESENTED BY:
PUSHKRAJ RANE (18162152)
RISHIKESH SALI (18162158)
VISHAL SANGALE (18162161)
Guided by:
Dr. Sandhya Jadhav

2. INDEX
• Introduction
• Problem statement
• Objectives of Study
• Literature review
• Methodology
• Research and Calculation
• Results obtained
• Outcomes through the research.

3. Introduction
• Cracks commonly occur in engineered parts and can significantly reduce their
ability to withstand load. Cracks typically form around pre-existing flaws in a part.
They usually start off small and then grow during operational use.
• A crack in a part will grow under conditions of cyclic applied loading, or under a
steady load in a hostile chemical environment. Crack growth due to cyclic loading
is called fatigue crack growth and is the focus of this study. Crack growth in a
hostile environment is called environmental crack growth and is not included in the
this case study project.
• The analysis of fatigue crack growth relies on the concepts of fracture mechanics.

4. Problem statement
• It is usually really difficult for anyone to predict the life of a
particular metal element considering it to be damaged due to
presence of crack which are visible on the surface.
• Due to presence of cracks, the strength of the component as whole
gradually decreases as the propagation of crack is expected due to
the constantly acting fatigue loads on the entire component and
prediction of the direction of crack expansion is also really difficult.
• A crack on a railway track is extremely dangerous as it may cause a
huge accident, hence after locating a crack it is necessary to estimate
the life of the component in order to know how long it could be in a
working condition.

5. • Incase of an railway track crack, the expansion and crack
propagation rate is extremely high.
• Due to extremely high cyclic/fatigue loading on the tracks, the cracks
seem to propagate at faster rate hence quick action has to be taken to
determine the remaining life of the component in order to take
necessary actions.

6. Objectives of the Study
• To simulate and try to find a faster way to find the life
expectancy of cracked metal component under the
allowable factor of safety in working condition.
• Taking a case of a railway track crack and analyzing the
effect and growth of the crack due to constantly acting
fatigue load.

7. Literature review
 Research paper on ‘Fatigue crack growth’
• The following study takes various loads and stresses in account along with
various stress ratios and it also establishes a relationship between crack
growth and the constant cyclic loading.
• The experimentation is done a metal plate with naturally visible crack due
to surface flaws, when the component is put to its usual operations, the
usual stresses start acting but, due the presence of crack, the life of the
component is gradually reduced and the growth rate of the crack is
minutely observed and the acting loads are also closely monitored.

8. • On the basis of obtained results of the crack growth in a certain time
under certain fatigue loading, a relationship of crack growth to
loading is established which makes it easier to determine the
remaining life of the component before it fails in the factor of safety
and becomes un-operational.
• Although the exact results from experimentation are not provided,
but the study does use previous research in fracture mechanics to
determine the life of the component and gives a brief theoretical
explanation on how the crack propagation/expansion takes place so
that the same method could be used to determine the same in other
cases by making the necessary changes such as material properties,
acting loads and the Factor of safety.

9. Research paper on
Rail fatigue crack propagation
 This Research paper focuses mainly on the
cracks and its effects on railway tracks.
The study through various methods and based on earlier
research and assumptions tries to effectively determine the behavior of
cracks when the wheels of trains make surface contact with them in a very
fast speed.
 In this study mostly finite element method is used to determine the effect
of loading at significant points on the crack in the component(track).
Using predefined Relations and formulae, the crack propagation is tracked
with the difference in the speed of train which increases/ decreases the
time that load acts on the railway track.

10. Methodology
• Data collection.
• Theoretical study of the concepts of fracture mechanics
• Research, Calculation and data interpretation.
• Detailed Analysis of obtained results.
• Co-relation of the results and concepts with case study.
• Conclusion of the Study.

11. Research and Calculations
 The research on Crack Propagation and its growth was carried out in a
systematic order by initially determining all the factors necessary for the
Calculation of life of the metal having a visible surface crack.
 Some of the Crucial Factors that were considered necessary after
thorough research for the determination of the results of this study were,
Stress Intensity Factor (Kmax)
Paris Equation

12. Crack Length Prediction
 The data required for the calculation were selected and the standard
values were assumed or selected wherever necessary by taking reference
of the earlier research papers.
 The calculation for the life expectancy of a metal with a crack started with
calculating the stress intensity followed by consideration of the forces
acting on the specimen, substitution of data in Paris equation and
calculating the final Crack length after completion of a given No. cycles of
cyclic load.
 The crack length obtained at the end is then used to check when the
specimen would fail and its Life expectancy.

13. Results in graphical method:
 The results of the graphical method could be shown through a graph,
where the Increasing no. of cycles (N) are denoted on X axis, whereas the
length of crack which increases simultaneously is shown on Y axis.
 The result obtained is a smooth rising curve.
 The points plotted are,
ai which denotes initial crack length which in this case is the notch length i.e 5
mm.
ao which denotes the increase in crack length, here its obtained as 20 mm.
af which denotes the final crack length (45 mm).

14.  The graph further rises and shows the breaking point of the material.
 The slopes obtained from the curve are also used in the process of
calculation in the numerical approach.

15. Results obtained
 The main focus of research was to understand the phenomenon of crack
propagation and fracture mechanics and hence for the purpose of
research a MS block was kept under cyclic loading and a notch was made
purposely for the crack to propagate further.
 The obtained result were as follows;
for a crack with initial crack length (notch length) was taken 5mm.
 The dimension of the MS block were 50*50*10 mm, with a 5 mm notch
on the center of edge on the face.
 A larger initial crack length was purposely selected in order to show the
intensity of crack growth because the presence of a micro crack and the
1st phase of crack expansion is concurrent but extremely slow.

16. Results obtained
 A small load of 25 N was selected for a large no. of cycles which was
assumed for initial calculations as 2000 cycles.
 After completion of a given no. of cycles the crack fully propagates into the
material through out its length, hence the final crack length excluding the
notch is 45mm.
 Both numeric and graphical method were used for calculation of the failure
point (Nf) i.e. the no. of cycles the block could withstand before failure.
 This Final crack length was used to further calculate the point of failure of the
component and the No. of cycles before failure.
 The Failure point (Nf) i.e. the no. of cycles the component could survive
before failure was 120 cycles.

17. DRAWING AND ANALYSIS
Stress concentration at position
of notch causing cracking of
material
Mild steel block of size
50 x 50 x 10

18. Project Timeline
1. Data collection and research till September.
2. Theoretical study and literature review in October and November.
3. Research and Calculations to be done in November and December 2020.
4. Study and review of the obtained result to be done in December- January.
5. Conclusion of study and preparation of black book in February and
march 2021.

19. Expected outcomes
 To provide a detailed understanding about the concepts of
fracture mechanics and the behavior of cracks and its
effect on usual operations.
 To find ways to calculate the life of component having
cracks more effectively by using pre-existing relations,
concepts for taking necessary actions faster.

20. Thank you