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2007-01-0258 
Dynamic Load and Stress Analysis of a Crankshaft 
Farzin H. Montazersadgh and Ali Fatemi 
The University of Toledo 
Copyright © 2007 SAE International 
ABSTRACT 
In this study a dynamic simulation was conducted on a 
crankshaft from a single cylinder four stroke engine. 
Finite element analysis was performed to obtain the 
variation of stress magnitude at critical locations. The 
pressure-volume diagram was used to calculate the load 
boundary condition in dynamic simulation model, and 
other simulation inputs were taken from the engine 
specification chart. The dynamic analysis was done 
analytically and was verified by simulation in ADAMS 
which resulted in the load spectrum applied to crank pin 
bearing. This load was applied to the FE model in 
ABAQUS, and boundary conditions were applied 
according to the engine mounting conditions. The 
analysis was done for different engine speeds and as a 
result critical engine speed and critical region on the 
crankshaft were obtained. Stress variation over the 
engine cycle and the effect of torsional load in the 
analysis were investigated. Results from FE analysis 
were verified by strain gages attached to several 
locations on the crankshaft. Results achieved from 
aforementioned analysis can be used in fatigue life 
calculation and optimization of this component. 
INTRODUCTION 
Crankshaft is a large component with a complex 
geometry in the engine, which converts the reciprocating 
displacement of the piston to a rotary motion with a four 
link mechanism. This study was conducted on a single 
cylinder four stroke cycle engine. 
Rotation output of an engine is a practical and applicable 
input to other devices since the linear displacement of 
an engine is not a smooth output as the displacement is 
caused by the combustion of gas in the combustion 
chamber. A crankshaft changes these sudden 
displacements to a smooth rotary output which is the 
input to many devices such as generators, pumps, 
compressors. 
A detailed procedure of obtaining stresses in the fillet 
area of a crankshaft was introduced by Henry et al. [1], 
in which FEM and BEM (Boundary Element Method) 
were used. Obtained stresses were verified by 
experimental results on a 1.9 liter turbocharged diesel 
engine with Ricardo type combustion chamber 
configuration. The crankshaft durability assessment tool 
used in this study was developed by RENAULT. The 
software used took into account torsional vibrations and 
internal centrifugal loads. Fatigue life predictions were 
made using the multiaxial Dang Van criterion. The 
procedure developed is such it that could be used for 
conceptual design and geometry optimization of 
crankshaft. 
Guagliano et al. [2] conducted a study on a marine 
diesel engine crankshaft, in which two different FE 
models were investigated. Due to memory limitations in 
meshing a three dimensional model was difficult and 
costly. Therefore, they used a bi-dimensional model to 
obtain the stress concentration factor which resulted in 
an accuracy of less than 6.9 percent error for a centered 
load and 8.6 percent error for an eccentric load. This 
numerical model was satisfactory since it was very fast 
and had good agreement with experimental results. 
Payer et al. [3] developed a two-step technique to 
perform nonlinear transient analysis of crankshafts 
combining a beam-mass model and a solid element 
model. Using FEA, two major steps were used to 
calculate the transient stress behavior of the crankshaft; 
the first step calculated time dependent deformations by 
a step-by-step integration using the newmark-beta-method. 
Using a rotating beam-mass-model of the 
crankshaft, a time dependent nonlinear oil film model 
and a model of the main bearing wall structure, the 
mass, damping and stiffness matrices were built at each 
time step and the equation system was solved by an 
iterative method. In the second step those transient 
deformations were enforced to a solid-element-model of 
the crankshaft to determine its time dependent stress 
behavior. The major advantage of using the two steps 
was reduction of CPU time for calculations. This is 
because the number of degrees of freedom for 
performing step one was low and therefore enabled an 
efficient solution. Furthermore, the stiffness matrix of the
2 
solid element model for step two needed only to be built 
up once. 
In order to estimate fatigue life of crankshafts, Prakash 
et al. [4] performed stress and fatigue analysis on three 
example parts belonging to three different classes of 
engines. The classical method of crankshaft stress 
analysis (by representing crankshaft as a series of rigid 
disks separated by stiff weightless shafts) and an FEM-based 
approach using ANSYS code were employed to 
obtain natural frequencies, critical modes and speeds, 
and stress amplitudes in the critical modes. A fatigue 
analysis was also performed and the effect of variation 
of fatigue properties of the material on failure of the parts 
was investigated. This was achieved by increasing each 
strain-life parameter (σf′, εf′, b and c) by 10% and 
estimating life. It was shown that strength and ductility 
exponents have a large impact on life, e.g. a 10% 
increase of b leads to 93% decrease in estimated life. 
A geometrically restricted model of a light automotive 
crankshaft was studied by Borges et al. [5]. The 
geometry of the crankshaft was geometrically restricted 
due to limitations in the computer resources available to 
the authors. The FEM analysis was performed in 
ANSYS software and a three dimensional model made 
of Photoelastic material with the same boundary 
conditions was used to verify the results. This study was 
based on static load analysis and investigated loading at 
a specific crank angle. The FE model results showed 
uniform stress distribution over the crank, and the only 
region with high stress concentration was the fillet 
between the crank-pin bearing and the crank web. 
Shenoy and Fatemi [6] conducted dynamic analysis of 
loads and stresses in the connecting rod component, 
which is in contact with the crankshaft. Dynamic analysis 
of the connecting rod is similar to dynamics of the 
crankshaft, since these components form a slide-crank 
mechanism and the connecting rod motion applies 
dynamic load on the crank-pin bearing. Their analysis 
was compared with commonly used static FEA and 
considerable differences were obtained between the two 
sets of analysis. Shenoy and Fatemi [7] optimized the 
connecting rod considering dynamic service load on the 
component. It was shown that dynamic analysis is the 
proper basis for fatigue performance calculation and 
optimization of dynamically loaded components. Since a 
crankshaft experiences similar loading conditions as a 
connecting rod, optimization potentials of a crankshaft 
could also be obtained by performing an analytical 
dynamic analysis of the component. 
A literature survey by Zoroufi and Fatemi [8] focused on 
durability performance evaluation and comparisons of 
forged steel and cast iron crankshafts. In this study 
operating conditions of crankshaft and various failure 
sources were reviewed, and effect of parameters such 
as residual stress and manufacturing procedure on the 
fatigue performance of crankshaft were discussed. In 
addition, durability performance of common crankshaft 
materials and manufacturing process technologies were 
compared and durability assessment procedure, bench 
testing, and experimental techniques used for 
crankshafts were discussed. Their review also included 
cost analysis and potential geometry optimizations of 
crankshaft. 
In this paper, first dynamic load analysis of the 
crankshaft investigated in this study is presented. This 
includes a discussion of the loading sources, as well as 
importance of torsion load produced relative to bending 
load. FE modeling of the crankshaft is presented next, 
including a discussion of static versus dynamic load 
analysis, as well as the boundary conditions used. 
Results from the FE model are then presented which 
includes identification of the critically stressed location, 
variation of stresses over an entire cycle, and a 
discussion of the effects of engine speed as well as 
torsional load on stresses. A comparison of FEA 
stresses with those obtained from strain gages of a 
crankshaft in a bench test is also presented. Finally, 
conclusions are drawn based on the analysis preformed 
and results presented. 
LOAD ANALYSIS 
The crankshaft investigated in this study is shown in 
Figure 1 and belongs to an engine with the configuration 
shown in Table 1 and piston pressure versus crankshaft 
angle shown in Figure 2. Although the pressure plot 
changes for different engine speeds, the maximum 
pressure which is much of our concern does not change 
and the same graph could be used for different speeds 
[9]. The geometries of the crankshaft and connecting rod 
from the same engine were measured with the accuracy 
of 0.0025 mm (0.0001 in) and were drawn in the I-DEAS 
software, which provided the solid properties of the 
connecting rod such as moment of inertia and center of 
gravity (CG). These data were used in ADAMS software 
to simulate the slider-crank mechanism. The dynamic 
analysis resulted in angular velocity and angular 
acceleration of the connecting rod and forces between 
the crankshaft and the connecting rod. 
Fx Fy 
Fz 
Figure 1: Crankshaft geometry and bending (Fx), 
torsional (Fy), and longitudinal (Fz) force directions
3 
Table 1: Configuration of the engine to which the 
crankshaft belongs 
Crankshaft radius 37 mm 
Piston Diameter 89 mm 
Mass of the connecting rod 0.283 kg 
Mass of the piston assembly 0.417 kg 
Connecting rod length 120.78 mm 
Izz of connecting rod about the 
center of gravity 0.663×10-3 kg-m2 
Distance of C.G. of connecting 
rod from crank end center 28.6 mm 
Maximum gas pressure 35 Bar 
40 
35 
30 
25 
20 
15 
10 
5 
0 
0 100 200 300 400 500 600 700 
Crankshaft Angle (Deg) 
Cylinder Pressure (bar) 
Figure 2: Piston pressure versus crankshaft angle 
diagram used to calculate forces at the connecting rod 
ends 
There are two different load sources acting on the 
crankshaft. Inertia of rotating components (e.g. 
connecting rod) applies forces to the crankshaft and this 
force increases with the increase of engine speed. This 
force is directly related to the rotating speed and 
acceleration of rotating components. Variation of angular 
acceleration and angular velocity of the connecting rod 
for the engine speed of 3600 rpm is shown in Figure 3. 
The second load source is the force applied to the 
crankshaft due to gas combustion in the cylinder. The 
slider-crank mechanism transports the pressure applied 
to the upper part of the slider to the joint between 
crankshaft and connecting rod. This transmitted load 
depends on the dimensions of the mechanism. 
100 
80 
60 
40 
20 
0 
-20 
-40 
-60 
-80 
-100 
40000 
30000 
20000 
10000 
0 
Velocity 
0 180 360 540 720 
Acceleration 
Crankshaft Angle (Deg) 
Angular Velocity (rad/s) 
-10000 
-20000 
-30000 
-40000 
Angular Acceleration (rad/s^2) 
Figure 3: Variation of angular velocity and angular 
acceleration of the connecting rod over one complete 
engine cycle at a crankshaft speed of 2800 rpm 
Forces applied to the crankshaft cause bending and 
torsion. Figure 1 demonstrates the positive directions 
and local axis on the contact surface with the connecting 
rod. Figure 4 shows the variations of bending and 
torsion loads and the magnitude of the total force 
applied to the crankshaft as a function of crankshaft 
angle for the engine speed of 3600 rpm. The maximum 
load which happens at 355 degrees is where 
combustion takes place, at this moment the acting force 
on the crankshaft is just bending load since the direction 
of the force is exactly toward the center of the crank 
radius (i.e. Fy = 0 in Figure 1). This maximum load 
situation happens in all types of engines with a slight 
difference in the crank angle. In addition, most analysis 
done on engines with more cylinders (e.g. 4, 6, and 8) is 
on a portion of the crankshaft that consists of two main 
journal bearings, two crank webs, and a connecting rod 
pin journal. Therefore, analysis done for this single 
cylinder engine can be extended to larger engines. 
20 
15 
10 
5 
0 
-5 
-10 
Total 
0 100 200 300 400 500 600 700 
Bending Torsional 
Crankshaft Angle (Deg) 
Force (kN) 
Figure 4: Bending, torsional, and the resultant force at 
the connecting rod bearing at the engine speed of 3600 
rpm
4 
In many studies the torsional load is neglected for the 
load analysis of the crankshaft, and this is because 
torsional load is less than 10 percent of the bending load 
[10]. In this specific engine with its dynamic loading, it is 
shown in the next sections that torsional load has no 
effect on the range of von Mises stress at the critical 
location. The main reason of torsional load not having 
much effect on the stress range is that the maxima of 
bending and torsional loading happen at different times 
(see Figure 4). In addition, when the peak of the bending 
load takes place the magnitude of torsional load is zero. 
Figure 5 compares the magnitude of maximum torsional 
and bending loads at different engine speeds. As can be 
seen in this figure, the maximum of total load magnitude, 
which is equal to the maximum of bending load 
decreases as the engine speed increases. The reason 
for this situation refers to the load sources that exist in 
the engine at 355 degree crank angle. At this crank 
angle these two forces act in opposite directions. The 
force caused by combustion which is greater than the 
inertia load does not change at different engine speeds 
since the same pressure versus crankshaft angle is 
used for all engine speeds. The load caused by inertia 
increases in magnitude as the engine speed increases. 
Therefore, as the engine speed increases, a larger 
magnitude of inertia force is deducted from the 
combustion load, resulting in a decrease of the total load 
magnitude. 
25 
20 
15 
10 
5 
0 
2000 2800 3600 
Engine Speed (RPM) 
Force Magnitude (kN) 
Max Bending Max Torsion Range of Bending Range of Torsion 
Figure 5: Comparison of maximum and range of bending 
and torsional loads at different engine speeds 
FE MODELING OF THE CRANKSHAFT 
The FE model of the crankshaft geometry has about 105 
quadratic tetrahedral elements, with the global element 
length of 5.08 mm and local element length of 0.762 mm 
at the fillets where the stresses are higher due to stress 
concentrations. As a crankshaft is designed for very long 
life, stresses must be in the linear elastic range of the 
material. Therefore, all carried analysis are based on the 
linear properties of the crankshaft material. The meshed 
crankshaft with 122,441 elements is shown in Figure 6. 
The dynamic loading of the crankshaft is complicated 
because the magnitude and direction of the load 
changes during a cycle. There are two ways to find the 
stresses in dynamic loading. One method is running the 
FE model as many times as possible with the direction 
and magnitude of the dynamic force. An alternative and 
simpler way of obtaining stress components is 
superposition of static loading. The main idea of 
superposition is finding the basic loading positions, then 
applying unit load on each position according to dynamic 
loading of the crankshaft, and scaling and combining the 
stresses from each unit load. In this study both methods 
were used with 13 points over 720 degrees of crankshaft 
angle. The results from 6 different locations on the 
crankshaft showed identical stress components from the 
two methods. 
Figure 6: FEA model of the crankshaft with fine mesh in 
fillet areas 
It should be noted that the analysis is based on dynamic 
loading, though each finite element analysis step is done 
in static equilibrium. The main advantage of this kind of 
analysis is more accurate estimation of the maximum 
and minimum loads. Design and analyzes of the 
crankshaft based on static loading can lead to very 
conservative results. In addition, as was shown in this 
section, the minimum load could be achieved only if the 
analysis of loading is carried out during the entire cycle. 
The minimum value of von Mises stress which is 
obtained at the minimum load is needed for the stress 
range calculation and considering it zero will lead to 
smaller values for the stress range. 
As the dynamic loading condition is analyzed, only two 
main loading conditions are applied to the surface of the 
crankpin bearing. These two loads are perpendicular to 
each other and their directions are shown in Figure 1 as
5 
Fx and Fy. Since the contact surface between connecting 
rod and crankpin bearing does not carry tension, Fx and 
Fy can also act in the opposite direction to those shown 
in Figure 1. Any loading condition during the service life 
of the crankshaft can be obtained by scaling and 
combining the magnitude and direction of these two 
loads. 
Boundary conditions in the FE model were based on the 
engine configuration. The mounting of this specific 
crankshaft is on two different bearings which results in 
different constraints in the boundary conditions. One 
side of the crankshaft is fixed to the engine block by a 
ball bearing and the other side is rolling over a journal 
bearing. When under load, only 180 degrees of the 
bearing surfaces facing the load direction constraint the 
motion of the crankshaft. Therefore, a fixed semicircular 
surface as wide as the ball bearing width was used to 
model that section. This indicates that the surface can 
not move in either direction and can not rotate. The 
other side was modeled as a fixed thin semicircular ring 
which only holds the crankshaft centerline in its original 
position and acts as a pivot joint. In other words, the 
journal bearing is modeled in a way that allows the 
crankshaft to rotate about axis 1 as well as slide in 
direction 3 as occurs in a journal bearing. These defined 
boundary conditions are shown in Figure 7. Boundary 
conditions rotate with the direction of the load applied. 
Applied load; constant 
pressure over 120° 
Figure 7: Boundary conditions used in the FEA model 
RESULTS AND DISCUSSION OF STRESS 
ANALYSIS 
Some locations on the geometry were considered for 
depicting the stress history. These locations were 
selected according to the results of FE analysis, and as 
expected, all the selected elements are located on 
different parts of the fillet areas due to the high stress 
concentrations at these locations. Selected locations are 
labeled in Figure 8 and the von Mises stresses with sign 
for these elements are plotted in Figure 9. The critical 
loading situation is at the crank angle of 355 where the 
combustion exerts a large impact on the piston. At this 
time all stresses are at their highest level during stress 
time history in a cycle. As can be seen, location number 
2 experiences the highest stress at this moment. 
Therefore, element number 2 was selected as the critical 
element. Figure 10 shows the maximum stress, mean 
stress, and stress range at the engine speed of 2000 
rpm at different locations. It can be seen that element 
number 2 not only has the maximum von Mises stress, 
but it also carries the largest stress range and mean 
stress among other locations. This is important in fatigue 
analysis since the range and mean stress have more 
influence than the maximum stress. This is another 
reason for why having the stress history of critical 
elements are more useful than static analysis of the 
crankshaft. 
5 
c d 
Figure 8: Locations on the crankshaft where the stress 
variation was traced over one complete cycle of the 
engine, and locations where strain gages were mounted 
200 
150 
100 
50 
0 
-50 
0 180 360 540 720 
Crankshaft Angle (Deg) 
Stress Magnitude (MPa) 
1 2 3 4 5 6 
Figure 9: von Mises stress history (considering sign of 
principal stress) at different locations at the engine 
speed of 2000 rpm 
Fixed surface 
in all degrees 
of freedom 
over 180 Fixed ring in o 
directions 1 & 2 
over 180o 
1 
2 
3 
6 
3 
2 
1 
A 
A 
A-A 
a 
b 
7
6 
250 
200 
150 
100 
50 
0 
-50 
1 2 3 4 5 6 
Location Number 
Stress Magnitude (MPa) 
Maximum Minimum Range Mean 
Figure 10: Comparison of maximum, minimum, mean, 
and range of stress at the engine speed of 2000 rpm at 
different locations on the crankshaft 
Figure 11 shows the effect of engine speed on minimum, 
maximum, mean and range of stress. This figure 
indicates the higher the engine speed, the lower the von 
Mises stress. It should, however, be noted that there are 
many other factors regarding service life of an engine. 
Other important factors when the engine speed 
increases are wear and lubrication. As these issues 
were not of concern in this study, further discussion is 
avoided. 
250 
200 
150 
100 
50 
0 
-50 
1500 2000 2500 3000 3500 4000 
Engine Speed (RPM) 
von Mises Stress Magnitude (MPa) 
Min Max Mean Range 
Figure 11: Variation of minimum stress, maximum 
stress, mean stress, and stress range at location 2 on 
the crankshaft as a function of engine speed 
The effect of torsional load was discussed in the load 
analysis section, and was pointed out that it has no 
effect on the stress range of the critical location. The von 
Mises stress at location number 2 shown in Figure 9 
remains the same with and without considering torsional 
load. This is due to the location of the critical point which 
is not influenced by torsion since it is located on the 
crankpin bearing. Other locations such as 1, 6, and 7 in 
Figure 8 experience the torsional load. Figure 12 shows 
changes in minimum, maximum, mean, and range of 
von Mises stress at location 7 with considering torsion 
and without considering it during service life at two 
different engine speeds. It can be seen that the 
minimum von Mises stress does not change since the 
minimum happens at a time when the torsional load is 
zero. The effect of torsion is about 16 percent increase 
in the stress range at this location. 
100 
80 
60 
40 
20 
0 
-20 
-40 
-60 
-80 
2000 3600 
Engine Speed (RPM) 
Stress Magnitude (MPa) 
Total min stress Min stress without Torsion 
Total max stress Max stress without Torsion 
Total stress range Stress range without Torsion 
Total mean stress Mean stress without torsion 
Figure 12: Effect of considering torsion in stresses at 
location 7 at different engine speeds 
Stress results obtained from the FE model were verified 
by experimental component test. Strain gages were 
mounted at four locations on the crankpin bearing. 
These locations are labeled as a, b, c, and d in Figure 8. 
The FE model boundary conditions were changed 
according to the fixture of the test assembly. The fixture 
constraints the motion of the shaft on the left side of the 
crankshaft in Figure 8 and a load is applied on the right 
side of the crankshaft with a moment arm of 44 cm. 
Therefore, the crankshaft is experiencing bending as a 
cantilever beam. Applying load in the direction of axis 2 
in Figure 7 will result in stresses at locations a and b, 
and applying load in the direction of axis 1 in the same 
figure will result in stresses at locations c and d. 
Analytical calculations based on pure bending equation, 
Mc/I, show the magnitude of stresses to be the same 
and equal to 72 MPa at these locations, for a 890 N 
load. The values obtained from experiments are 
tabulated in Table 2. FEA results are also shown and 
compared with experimental results in this table. As can 
be seen, differences between FEA and strain gage 
results are less than 7 percent for different loading
7 
conditions. This is an indication of the accuracy of the 
FE model used in this study. 
Table 2: Comparison of stress results from FEA and 
strain gages located at positions shown in Figure 8 
Load Location a Location b 
(N) FEA 
(MPa) 
EXP 
(MPa) 
% 
Difference 
FEA 
(MPa) 
EXP 
(MPa) 
% 
Difference 
-890 -61.6 -59.3 3.8% 86.9 81.4 6.4% 
890 61.5 65.5 6.5% -86.7 -90.3 4.2% 
Load Location c Location d 
(N) FEA 
(MPa) 
EXP 
(MPa) 
% 
Difference 
FEA 
(MPa) 
EXP 
(MPa) 
% 
Difference 
-890 -76.4 -71.7 6.1% 75.5 71.7 5.0% 
890 76.3 75.8 0.5% -75.6 -76.5 1.3% 
Comparison of stresses at locations c and d resulting 
from loading in direction 1 in Figure 7 show symmetric 
stress values from FEA, experiment, and analytical 
method. The results from these three methods are close 
to each other. However, stresses obtained form FEA 
results and experiment show different stresses (i.e. non-symmetric) 
at locations a and b, resulting from loading in 
direction 2 in Figure 7. On the other hand, stresses 
calculated from the analytical method are symmetric at 
these two locations (+/-72 MPa) and different from the 
obtained values from FEA and experiment. Therefore, 
the use of FE model in the analysis is necessary due to 
geometry complexity. 
Stress results from FE and analytical results have similar 
symmetric values for stresses on the main bearing away 
from fillet areas. FE results show different stress values 
on the fillet area of main bearing. The reason is the 
eccentric cylinders geometry which will result in changes 
in Kt value around the fillet area. 
Load variation over a cycle results in variation of stress. 
For proper calculations of fatigue damage in the 
component there is a need for a cycle counting method 
over the stress history. Using the rainflow counting 
method [11] on the critical stress history plot (i.e. 
location 2 in Figure 9) shows that in an entire cycle only 
one peak is important and can cause fatigue damage in 
the component. The result of the rain count flow over the 
stress-time history of location 2 at the engine speed of 
2000 rpm is shown in Figure 13. It is shown in this figure 
that in the stress history of the critical location only one 
cycle of loading is important and the other minor cycles 
have low stress amplitudes. 
1 
2 
3 
5 
6 
7 9 10 11 
200 
150 
100 
50 
0 
-50 
0 2 4 6 8 10 12 
Time 
von Mises Stress Magnitude (MPa) 
Figure 13: Rain flow count of the von Mises stress with 
consideration of sign at location 2 at engine speed of 
2000 rpm 
CONCLUSIONS 
The following conclusions could be drawn from this 
study: 
1. Dynamic loading analysis of the crankshaft results in 
more realistic stresses whereas static analysis 
provides an overestimate results. Accurate stresses 
are critical input to fatigue analysis and optimization 
of the crankshaft. 
2. There are two different load sources in an engine; 
inertia and combustion. These two load source 
cause both bending and torsional load on the 
crankshaft. 
3. The maximum load occurs at the crank angle of 355 
degrees for this specific engine. At this angle only 
bending load is applied to the crankshaft. 
4. Considering torsional load in the overall dynamic 
loading conditions has no effect on von Mises stress 
at the critically stressed location. The effect of 
torsion on the stress range is also relatively small at 
other locations undergoing torsional load. Therefore, 
the crankshaft analysis could be simplified to 
applying only bending load. 
5. Critical locations on the crankshaft geometry are all 
located on the fillet areas because of high stress 
gradients in these locations which result in high 
stress concentration factors. 
6. Superposition of FEM analysis results from two 
perpendicular loads is an efficient and simple 
method of achieving stresses at different loading 
conditions according to forces applied to the 
crankshaft in dynamic analysis. 
7. Experimental and FEA results showed close 
agreement, within 7% difference. These results 
indicate non-symmetric bending stresses on the 
crankpin bearing, whereas using analytical method 
predicts bending stresses to be symmetric at this 
location. The lack of symmetry is a geometry 
deformation effect, indicating the need for FEA
8 
modeling due to the relatively complex geometry of 
the crankshaft. 
8. Using the rainflow cycle counting method on the 
critical stress history plot shows that in an entire 
cycle only one peak is important and can cause 
fatigue damage in the component. 
REFERENCES 
1. Henry, J., Topolsky, J., and Abramczuk, M., 1992, 
“Crankshaft Durability Prediction – A New 3-D 
Approach,” SAE Technical Paper No. 920087, 
Society of Automotive Engineers 
2. Guagliano, M., Terranova, A., and Vergani, L., 1993, 
“Theoretical and Experimental Study of the Stress 
Concentration Factor in Diesel Engine Crankshafts,” 
Journal of Mechanical Design, Vol. 115, pp. 47-52 
3. Payar, E., Kainz, A., and Fiedler, G. A., 1995, 
“Fatigue Analysis of Crankshafts Using Nonlinear 
Transient Simulation Techniques,” SAE Technical 
Paper No. 950709, Society of Automotive Engineers 
4. Prakash, V., Aprameyan, K., and Shrinivasa, U., 
1998, “An FEM Based Approach to Crankshaft 
Dynamics and Life Estimation,” SAE Technical 
Paper No. 980565, Society of Automotive Engineers 
5. Borges, A. C. C., Oliveira, L. C., and Neto, P. S., 
2002, “Stress Distribution in a Crankshaft Crank 
Using a Geometrucally Restricted Finite Element 
Model”, SAE Technical Paper No. 2002-01-2183, 
Society of Automotive Engineers 
6. Shenoy, P. S. and Fatemi, A., 2006, “Dynamic 
analysis of loads and stresses in connecting rods,” 
IMechE, Journal of Mechanical Engineering 
Science, Vol. 220, No. 5, pp. 615-624 
7. Shenoy, P. S. and Fatemi, A., "Connecting Rod 
Optimization for Weight and Cost Reduction", SAE 
Paper No. 2005-01-0987, SAE 2005 Transactions: 
Journal of Materials and Manufacturing 
8. Zoroufi, M. and Fatemi, A., "A Literature Review on 
Durability Evaluation of Crankshafts Including 
Comparisons of Competing Manufacturing 
Processes and Cost Analysis", 26th Forging Industry 
Technical Conference, Chicago, IL, November 2005 
9. Fergusen, C. R., 1986, “Internal Combustion 
Engines, Applied Thermo Science,” John Wiley and 
Sons, New York, NY, USA 
10. Jensen, E. J., 1970, “Crankshaft strength through 
laboratory testing,” SAE Technical Paper No. 
700526, Society of Automotive Engineers 
11. Stephens, R. I., Fatemi, A., Stephens, R. R., and 
Fuchs, H. O., 2001, “Metal Fatigue in Engineering,” 
2nd edition, John Wiley and Sons, New York, NY, 
USA

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Bhushjan

  • 1. 1 2007-01-0258 Dynamic Load and Stress Analysis of a Crankshaft Farzin H. Montazersadgh and Ali Fatemi The University of Toledo Copyright © 2007 SAE International ABSTRACT In this study a dynamic simulation was conducted on a crankshaft from a single cylinder four stroke engine. Finite element analysis was performed to obtain the variation of stress magnitude at critical locations. The pressure-volume diagram was used to calculate the load boundary condition in dynamic simulation model, and other simulation inputs were taken from the engine specification chart. The dynamic analysis was done analytically and was verified by simulation in ADAMS which resulted in the load spectrum applied to crank pin bearing. This load was applied to the FE model in ABAQUS, and boundary conditions were applied according to the engine mounting conditions. The analysis was done for different engine speeds and as a result critical engine speed and critical region on the crankshaft were obtained. Stress variation over the engine cycle and the effect of torsional load in the analysis were investigated. Results from FE analysis were verified by strain gages attached to several locations on the crankshaft. Results achieved from aforementioned analysis can be used in fatigue life calculation and optimization of this component. INTRODUCTION Crankshaft is a large component with a complex geometry in the engine, which converts the reciprocating displacement of the piston to a rotary motion with a four link mechanism. This study was conducted on a single cylinder four stroke cycle engine. Rotation output of an engine is a practical and applicable input to other devices since the linear displacement of an engine is not a smooth output as the displacement is caused by the combustion of gas in the combustion chamber. A crankshaft changes these sudden displacements to a smooth rotary output which is the input to many devices such as generators, pumps, compressors. A detailed procedure of obtaining stresses in the fillet area of a crankshaft was introduced by Henry et al. [1], in which FEM and BEM (Boundary Element Method) were used. Obtained stresses were verified by experimental results on a 1.9 liter turbocharged diesel engine with Ricardo type combustion chamber configuration. The crankshaft durability assessment tool used in this study was developed by RENAULT. The software used took into account torsional vibrations and internal centrifugal loads. Fatigue life predictions were made using the multiaxial Dang Van criterion. The procedure developed is such it that could be used for conceptual design and geometry optimization of crankshaft. Guagliano et al. [2] conducted a study on a marine diesel engine crankshaft, in which two different FE models were investigated. Due to memory limitations in meshing a three dimensional model was difficult and costly. Therefore, they used a bi-dimensional model to obtain the stress concentration factor which resulted in an accuracy of less than 6.9 percent error for a centered load and 8.6 percent error for an eccentric load. This numerical model was satisfactory since it was very fast and had good agreement with experimental results. Payer et al. [3] developed a two-step technique to perform nonlinear transient analysis of crankshafts combining a beam-mass model and a solid element model. Using FEA, two major steps were used to calculate the transient stress behavior of the crankshaft; the first step calculated time dependent deformations by a step-by-step integration using the newmark-beta-method. Using a rotating beam-mass-model of the crankshaft, a time dependent nonlinear oil film model and a model of the main bearing wall structure, the mass, damping and stiffness matrices were built at each time step and the equation system was solved by an iterative method. In the second step those transient deformations were enforced to a solid-element-model of the crankshaft to determine its time dependent stress behavior. The major advantage of using the two steps was reduction of CPU time for calculations. This is because the number of degrees of freedom for performing step one was low and therefore enabled an efficient solution. Furthermore, the stiffness matrix of the
  • 2. 2 solid element model for step two needed only to be built up once. In order to estimate fatigue life of crankshafts, Prakash et al. [4] performed stress and fatigue analysis on three example parts belonging to three different classes of engines. The classical method of crankshaft stress analysis (by representing crankshaft as a series of rigid disks separated by stiff weightless shafts) and an FEM-based approach using ANSYS code were employed to obtain natural frequencies, critical modes and speeds, and stress amplitudes in the critical modes. A fatigue analysis was also performed and the effect of variation of fatigue properties of the material on failure of the parts was investigated. This was achieved by increasing each strain-life parameter (σf′, εf′, b and c) by 10% and estimating life. It was shown that strength and ductility exponents have a large impact on life, e.g. a 10% increase of b leads to 93% decrease in estimated life. A geometrically restricted model of a light automotive crankshaft was studied by Borges et al. [5]. The geometry of the crankshaft was geometrically restricted due to limitations in the computer resources available to the authors. The FEM analysis was performed in ANSYS software and a three dimensional model made of Photoelastic material with the same boundary conditions was used to verify the results. This study was based on static load analysis and investigated loading at a specific crank angle. The FE model results showed uniform stress distribution over the crank, and the only region with high stress concentration was the fillet between the crank-pin bearing and the crank web. Shenoy and Fatemi [6] conducted dynamic analysis of loads and stresses in the connecting rod component, which is in contact with the crankshaft. Dynamic analysis of the connecting rod is similar to dynamics of the crankshaft, since these components form a slide-crank mechanism and the connecting rod motion applies dynamic load on the crank-pin bearing. Their analysis was compared with commonly used static FEA and considerable differences were obtained between the two sets of analysis. Shenoy and Fatemi [7] optimized the connecting rod considering dynamic service load on the component. It was shown that dynamic analysis is the proper basis for fatigue performance calculation and optimization of dynamically loaded components. Since a crankshaft experiences similar loading conditions as a connecting rod, optimization potentials of a crankshaft could also be obtained by performing an analytical dynamic analysis of the component. A literature survey by Zoroufi and Fatemi [8] focused on durability performance evaluation and comparisons of forged steel and cast iron crankshafts. In this study operating conditions of crankshaft and various failure sources were reviewed, and effect of parameters such as residual stress and manufacturing procedure on the fatigue performance of crankshaft were discussed. In addition, durability performance of common crankshaft materials and manufacturing process technologies were compared and durability assessment procedure, bench testing, and experimental techniques used for crankshafts were discussed. Their review also included cost analysis and potential geometry optimizations of crankshaft. In this paper, first dynamic load analysis of the crankshaft investigated in this study is presented. This includes a discussion of the loading sources, as well as importance of torsion load produced relative to bending load. FE modeling of the crankshaft is presented next, including a discussion of static versus dynamic load analysis, as well as the boundary conditions used. Results from the FE model are then presented which includes identification of the critically stressed location, variation of stresses over an entire cycle, and a discussion of the effects of engine speed as well as torsional load on stresses. A comparison of FEA stresses with those obtained from strain gages of a crankshaft in a bench test is also presented. Finally, conclusions are drawn based on the analysis preformed and results presented. LOAD ANALYSIS The crankshaft investigated in this study is shown in Figure 1 and belongs to an engine with the configuration shown in Table 1 and piston pressure versus crankshaft angle shown in Figure 2. Although the pressure plot changes for different engine speeds, the maximum pressure which is much of our concern does not change and the same graph could be used for different speeds [9]. The geometries of the crankshaft and connecting rod from the same engine were measured with the accuracy of 0.0025 mm (0.0001 in) and were drawn in the I-DEAS software, which provided the solid properties of the connecting rod such as moment of inertia and center of gravity (CG). These data were used in ADAMS software to simulate the slider-crank mechanism. The dynamic analysis resulted in angular velocity and angular acceleration of the connecting rod and forces between the crankshaft and the connecting rod. Fx Fy Fz Figure 1: Crankshaft geometry and bending (Fx), torsional (Fy), and longitudinal (Fz) force directions
  • 3. 3 Table 1: Configuration of the engine to which the crankshaft belongs Crankshaft radius 37 mm Piston Diameter 89 mm Mass of the connecting rod 0.283 kg Mass of the piston assembly 0.417 kg Connecting rod length 120.78 mm Izz of connecting rod about the center of gravity 0.663×10-3 kg-m2 Distance of C.G. of connecting rod from crank end center 28.6 mm Maximum gas pressure 35 Bar 40 35 30 25 20 15 10 5 0 0 100 200 300 400 500 600 700 Crankshaft Angle (Deg) Cylinder Pressure (bar) Figure 2: Piston pressure versus crankshaft angle diagram used to calculate forces at the connecting rod ends There are two different load sources acting on the crankshaft. Inertia of rotating components (e.g. connecting rod) applies forces to the crankshaft and this force increases with the increase of engine speed. This force is directly related to the rotating speed and acceleration of rotating components. Variation of angular acceleration and angular velocity of the connecting rod for the engine speed of 3600 rpm is shown in Figure 3. The second load source is the force applied to the crankshaft due to gas combustion in the cylinder. The slider-crank mechanism transports the pressure applied to the upper part of the slider to the joint between crankshaft and connecting rod. This transmitted load depends on the dimensions of the mechanism. 100 80 60 40 20 0 -20 -40 -60 -80 -100 40000 30000 20000 10000 0 Velocity 0 180 360 540 720 Acceleration Crankshaft Angle (Deg) Angular Velocity (rad/s) -10000 -20000 -30000 -40000 Angular Acceleration (rad/s^2) Figure 3: Variation of angular velocity and angular acceleration of the connecting rod over one complete engine cycle at a crankshaft speed of 2800 rpm Forces applied to the crankshaft cause bending and torsion. Figure 1 demonstrates the positive directions and local axis on the contact surface with the connecting rod. Figure 4 shows the variations of bending and torsion loads and the magnitude of the total force applied to the crankshaft as a function of crankshaft angle for the engine speed of 3600 rpm. The maximum load which happens at 355 degrees is where combustion takes place, at this moment the acting force on the crankshaft is just bending load since the direction of the force is exactly toward the center of the crank radius (i.e. Fy = 0 in Figure 1). This maximum load situation happens in all types of engines with a slight difference in the crank angle. In addition, most analysis done on engines with more cylinders (e.g. 4, 6, and 8) is on a portion of the crankshaft that consists of two main journal bearings, two crank webs, and a connecting rod pin journal. Therefore, analysis done for this single cylinder engine can be extended to larger engines. 20 15 10 5 0 -5 -10 Total 0 100 200 300 400 500 600 700 Bending Torsional Crankshaft Angle (Deg) Force (kN) Figure 4: Bending, torsional, and the resultant force at the connecting rod bearing at the engine speed of 3600 rpm
  • 4. 4 In many studies the torsional load is neglected for the load analysis of the crankshaft, and this is because torsional load is less than 10 percent of the bending load [10]. In this specific engine with its dynamic loading, it is shown in the next sections that torsional load has no effect on the range of von Mises stress at the critical location. The main reason of torsional load not having much effect on the stress range is that the maxima of bending and torsional loading happen at different times (see Figure 4). In addition, when the peak of the bending load takes place the magnitude of torsional load is zero. Figure 5 compares the magnitude of maximum torsional and bending loads at different engine speeds. As can be seen in this figure, the maximum of total load magnitude, which is equal to the maximum of bending load decreases as the engine speed increases. The reason for this situation refers to the load sources that exist in the engine at 355 degree crank angle. At this crank angle these two forces act in opposite directions. The force caused by combustion which is greater than the inertia load does not change at different engine speeds since the same pressure versus crankshaft angle is used for all engine speeds. The load caused by inertia increases in magnitude as the engine speed increases. Therefore, as the engine speed increases, a larger magnitude of inertia force is deducted from the combustion load, resulting in a decrease of the total load magnitude. 25 20 15 10 5 0 2000 2800 3600 Engine Speed (RPM) Force Magnitude (kN) Max Bending Max Torsion Range of Bending Range of Torsion Figure 5: Comparison of maximum and range of bending and torsional loads at different engine speeds FE MODELING OF THE CRANKSHAFT The FE model of the crankshaft geometry has about 105 quadratic tetrahedral elements, with the global element length of 5.08 mm and local element length of 0.762 mm at the fillets where the stresses are higher due to stress concentrations. As a crankshaft is designed for very long life, stresses must be in the linear elastic range of the material. Therefore, all carried analysis are based on the linear properties of the crankshaft material. The meshed crankshaft with 122,441 elements is shown in Figure 6. The dynamic loading of the crankshaft is complicated because the magnitude and direction of the load changes during a cycle. There are two ways to find the stresses in dynamic loading. One method is running the FE model as many times as possible with the direction and magnitude of the dynamic force. An alternative and simpler way of obtaining stress components is superposition of static loading. The main idea of superposition is finding the basic loading positions, then applying unit load on each position according to dynamic loading of the crankshaft, and scaling and combining the stresses from each unit load. In this study both methods were used with 13 points over 720 degrees of crankshaft angle. The results from 6 different locations on the crankshaft showed identical stress components from the two methods. Figure 6: FEA model of the crankshaft with fine mesh in fillet areas It should be noted that the analysis is based on dynamic loading, though each finite element analysis step is done in static equilibrium. The main advantage of this kind of analysis is more accurate estimation of the maximum and minimum loads. Design and analyzes of the crankshaft based on static loading can lead to very conservative results. In addition, as was shown in this section, the minimum load could be achieved only if the analysis of loading is carried out during the entire cycle. The minimum value of von Mises stress which is obtained at the minimum load is needed for the stress range calculation and considering it zero will lead to smaller values for the stress range. As the dynamic loading condition is analyzed, only two main loading conditions are applied to the surface of the crankpin bearing. These two loads are perpendicular to each other and their directions are shown in Figure 1 as
  • 5. 5 Fx and Fy. Since the contact surface between connecting rod and crankpin bearing does not carry tension, Fx and Fy can also act in the opposite direction to those shown in Figure 1. Any loading condition during the service life of the crankshaft can be obtained by scaling and combining the magnitude and direction of these two loads. Boundary conditions in the FE model were based on the engine configuration. The mounting of this specific crankshaft is on two different bearings which results in different constraints in the boundary conditions. One side of the crankshaft is fixed to the engine block by a ball bearing and the other side is rolling over a journal bearing. When under load, only 180 degrees of the bearing surfaces facing the load direction constraint the motion of the crankshaft. Therefore, a fixed semicircular surface as wide as the ball bearing width was used to model that section. This indicates that the surface can not move in either direction and can not rotate. The other side was modeled as a fixed thin semicircular ring which only holds the crankshaft centerline in its original position and acts as a pivot joint. In other words, the journal bearing is modeled in a way that allows the crankshaft to rotate about axis 1 as well as slide in direction 3 as occurs in a journal bearing. These defined boundary conditions are shown in Figure 7. Boundary conditions rotate with the direction of the load applied. Applied load; constant pressure over 120° Figure 7: Boundary conditions used in the FEA model RESULTS AND DISCUSSION OF STRESS ANALYSIS Some locations on the geometry were considered for depicting the stress history. These locations were selected according to the results of FE analysis, and as expected, all the selected elements are located on different parts of the fillet areas due to the high stress concentrations at these locations. Selected locations are labeled in Figure 8 and the von Mises stresses with sign for these elements are plotted in Figure 9. The critical loading situation is at the crank angle of 355 where the combustion exerts a large impact on the piston. At this time all stresses are at their highest level during stress time history in a cycle. As can be seen, location number 2 experiences the highest stress at this moment. Therefore, element number 2 was selected as the critical element. Figure 10 shows the maximum stress, mean stress, and stress range at the engine speed of 2000 rpm at different locations. It can be seen that element number 2 not only has the maximum von Mises stress, but it also carries the largest stress range and mean stress among other locations. This is important in fatigue analysis since the range and mean stress have more influence than the maximum stress. This is another reason for why having the stress history of critical elements are more useful than static analysis of the crankshaft. 5 c d Figure 8: Locations on the crankshaft where the stress variation was traced over one complete cycle of the engine, and locations where strain gages were mounted 200 150 100 50 0 -50 0 180 360 540 720 Crankshaft Angle (Deg) Stress Magnitude (MPa) 1 2 3 4 5 6 Figure 9: von Mises stress history (considering sign of principal stress) at different locations at the engine speed of 2000 rpm Fixed surface in all degrees of freedom over 180 Fixed ring in o directions 1 & 2 over 180o 1 2 3 6 3 2 1 A A A-A a b 7
  • 6. 6 250 200 150 100 50 0 -50 1 2 3 4 5 6 Location Number Stress Magnitude (MPa) Maximum Minimum Range Mean Figure 10: Comparison of maximum, minimum, mean, and range of stress at the engine speed of 2000 rpm at different locations on the crankshaft Figure 11 shows the effect of engine speed on minimum, maximum, mean and range of stress. This figure indicates the higher the engine speed, the lower the von Mises stress. It should, however, be noted that there are many other factors regarding service life of an engine. Other important factors when the engine speed increases are wear and lubrication. As these issues were not of concern in this study, further discussion is avoided. 250 200 150 100 50 0 -50 1500 2000 2500 3000 3500 4000 Engine Speed (RPM) von Mises Stress Magnitude (MPa) Min Max Mean Range Figure 11: Variation of minimum stress, maximum stress, mean stress, and stress range at location 2 on the crankshaft as a function of engine speed The effect of torsional load was discussed in the load analysis section, and was pointed out that it has no effect on the stress range of the critical location. The von Mises stress at location number 2 shown in Figure 9 remains the same with and without considering torsional load. This is due to the location of the critical point which is not influenced by torsion since it is located on the crankpin bearing. Other locations such as 1, 6, and 7 in Figure 8 experience the torsional load. Figure 12 shows changes in minimum, maximum, mean, and range of von Mises stress at location 7 with considering torsion and without considering it during service life at two different engine speeds. It can be seen that the minimum von Mises stress does not change since the minimum happens at a time when the torsional load is zero. The effect of torsion is about 16 percent increase in the stress range at this location. 100 80 60 40 20 0 -20 -40 -60 -80 2000 3600 Engine Speed (RPM) Stress Magnitude (MPa) Total min stress Min stress without Torsion Total max stress Max stress without Torsion Total stress range Stress range without Torsion Total mean stress Mean stress without torsion Figure 12: Effect of considering torsion in stresses at location 7 at different engine speeds Stress results obtained from the FE model were verified by experimental component test. Strain gages were mounted at four locations on the crankpin bearing. These locations are labeled as a, b, c, and d in Figure 8. The FE model boundary conditions were changed according to the fixture of the test assembly. The fixture constraints the motion of the shaft on the left side of the crankshaft in Figure 8 and a load is applied on the right side of the crankshaft with a moment arm of 44 cm. Therefore, the crankshaft is experiencing bending as a cantilever beam. Applying load in the direction of axis 2 in Figure 7 will result in stresses at locations a and b, and applying load in the direction of axis 1 in the same figure will result in stresses at locations c and d. Analytical calculations based on pure bending equation, Mc/I, show the magnitude of stresses to be the same and equal to 72 MPa at these locations, for a 890 N load. The values obtained from experiments are tabulated in Table 2. FEA results are also shown and compared with experimental results in this table. As can be seen, differences between FEA and strain gage results are less than 7 percent for different loading
  • 7. 7 conditions. This is an indication of the accuracy of the FE model used in this study. Table 2: Comparison of stress results from FEA and strain gages located at positions shown in Figure 8 Load Location a Location b (N) FEA (MPa) EXP (MPa) % Difference FEA (MPa) EXP (MPa) % Difference -890 -61.6 -59.3 3.8% 86.9 81.4 6.4% 890 61.5 65.5 6.5% -86.7 -90.3 4.2% Load Location c Location d (N) FEA (MPa) EXP (MPa) % Difference FEA (MPa) EXP (MPa) % Difference -890 -76.4 -71.7 6.1% 75.5 71.7 5.0% 890 76.3 75.8 0.5% -75.6 -76.5 1.3% Comparison of stresses at locations c and d resulting from loading in direction 1 in Figure 7 show symmetric stress values from FEA, experiment, and analytical method. The results from these three methods are close to each other. However, stresses obtained form FEA results and experiment show different stresses (i.e. non-symmetric) at locations a and b, resulting from loading in direction 2 in Figure 7. On the other hand, stresses calculated from the analytical method are symmetric at these two locations (+/-72 MPa) and different from the obtained values from FEA and experiment. Therefore, the use of FE model in the analysis is necessary due to geometry complexity. Stress results from FE and analytical results have similar symmetric values for stresses on the main bearing away from fillet areas. FE results show different stress values on the fillet area of main bearing. The reason is the eccentric cylinders geometry which will result in changes in Kt value around the fillet area. Load variation over a cycle results in variation of stress. For proper calculations of fatigue damage in the component there is a need for a cycle counting method over the stress history. Using the rainflow counting method [11] on the critical stress history plot (i.e. location 2 in Figure 9) shows that in an entire cycle only one peak is important and can cause fatigue damage in the component. The result of the rain count flow over the stress-time history of location 2 at the engine speed of 2000 rpm is shown in Figure 13. It is shown in this figure that in the stress history of the critical location only one cycle of loading is important and the other minor cycles have low stress amplitudes. 1 2 3 5 6 7 9 10 11 200 150 100 50 0 -50 0 2 4 6 8 10 12 Time von Mises Stress Magnitude (MPa) Figure 13: Rain flow count of the von Mises stress with consideration of sign at location 2 at engine speed of 2000 rpm CONCLUSIONS The following conclusions could be drawn from this study: 1. Dynamic loading analysis of the crankshaft results in more realistic stresses whereas static analysis provides an overestimate results. Accurate stresses are critical input to fatigue analysis and optimization of the crankshaft. 2. There are two different load sources in an engine; inertia and combustion. These two load source cause both bending and torsional load on the crankshaft. 3. The maximum load occurs at the crank angle of 355 degrees for this specific engine. At this angle only bending load is applied to the crankshaft. 4. Considering torsional load in the overall dynamic loading conditions has no effect on von Mises stress at the critically stressed location. The effect of torsion on the stress range is also relatively small at other locations undergoing torsional load. Therefore, the crankshaft analysis could be simplified to applying only bending load. 5. Critical locations on the crankshaft geometry are all located on the fillet areas because of high stress gradients in these locations which result in high stress concentration factors. 6. Superposition of FEM analysis results from two perpendicular loads is an efficient and simple method of achieving stresses at different loading conditions according to forces applied to the crankshaft in dynamic analysis. 7. Experimental and FEA results showed close agreement, within 7% difference. These results indicate non-symmetric bending stresses on the crankpin bearing, whereas using analytical method predicts bending stresses to be symmetric at this location. The lack of symmetry is a geometry deformation effect, indicating the need for FEA
  • 8. 8 modeling due to the relatively complex geometry of the crankshaft. 8. Using the rainflow cycle counting method on the critical stress history plot shows that in an entire cycle only one peak is important and can cause fatigue damage in the component. REFERENCES 1. Henry, J., Topolsky, J., and Abramczuk, M., 1992, “Crankshaft Durability Prediction – A New 3-D Approach,” SAE Technical Paper No. 920087, Society of Automotive Engineers 2. Guagliano, M., Terranova, A., and Vergani, L., 1993, “Theoretical and Experimental Study of the Stress Concentration Factor in Diesel Engine Crankshafts,” Journal of Mechanical Design, Vol. 115, pp. 47-52 3. Payar, E., Kainz, A., and Fiedler, G. A., 1995, “Fatigue Analysis of Crankshafts Using Nonlinear Transient Simulation Techniques,” SAE Technical Paper No. 950709, Society of Automotive Engineers 4. Prakash, V., Aprameyan, K., and Shrinivasa, U., 1998, “An FEM Based Approach to Crankshaft Dynamics and Life Estimation,” SAE Technical Paper No. 980565, Society of Automotive Engineers 5. Borges, A. C. C., Oliveira, L. C., and Neto, P. S., 2002, “Stress Distribution in a Crankshaft Crank Using a Geometrucally Restricted Finite Element Model”, SAE Technical Paper No. 2002-01-2183, Society of Automotive Engineers 6. Shenoy, P. S. and Fatemi, A., 2006, “Dynamic analysis of loads and stresses in connecting rods,” IMechE, Journal of Mechanical Engineering Science, Vol. 220, No. 5, pp. 615-624 7. Shenoy, P. S. and Fatemi, A., "Connecting Rod Optimization for Weight and Cost Reduction", SAE Paper No. 2005-01-0987, SAE 2005 Transactions: Journal of Materials and Manufacturing 8. Zoroufi, M. and Fatemi, A., "A Literature Review on Durability Evaluation of Crankshafts Including Comparisons of Competing Manufacturing Processes and Cost Analysis", 26th Forging Industry Technical Conference, Chicago, IL, November 2005 9. Fergusen, C. R., 1986, “Internal Combustion Engines, Applied Thermo Science,” John Wiley and Sons, New York, NY, USA 10. Jensen, E. J., 1970, “Crankshaft strength through laboratory testing,” SAE Technical Paper No. 700526, Society of Automotive Engineers 11. Stephens, R. I., Fatemi, A., Stephens, R. R., and Fuchs, H. O., 2001, “Metal Fatigue in Engineering,” 2nd edition, John Wiley and Sons, New York, NY, USA