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Volume-4, Issue-4, August-2014, ISSN No.: 2250-0758
International Journal of Engineering and Management Research
Available at:
www.ijemr.net
Page Number: 86-90
Static Stress Analysis and Optimization of a Diesel Engine Crankshaft using
FEA
Ramanagouda Biradar1, Dr. R A Savanur2
1M.Tech Scholar, Mechanical Engineering Department, BLDEA’s PGHCET Bijapur, Karnataka, INDIA 2 Professor and Head, Mechanical Engineering Department, BLDEA’s PGHCET Bijapur, Karnataka, INDIA
ABSTRACT
Crankshaft is one of the most critically loaded
component in the engine as it experiences cyclic loads in the form
of bending and torsion during its working condition. Its failure
will cause serious damage to the engine. So, its reliability
verification must be performed. This topic was chosen because
of increasing interest in the higher payloads, higher efficiency
and lower weight crankshafts.
The static stress analysis is conducted on a crankshaft
of a single-cylinder 4 stroke diesel engine using finite element
method. ANSYS WB14 is used for the analysis using 4 different
materials to find the distribution of maximum deformation,
maximum shear stress and von-mises stress on the crankshaft.
The results would provide a valuable foundation for the
optimization of mass and material selection.
Keywords: Crankshaft, FEM, Stress, Fillet, Optimization etc.
I. INTRODUCTION
In recent years, there are many kinds or development
of vehicle engine especially car and motorcycle engine. Each
automotive company tried to develop their own engine to
compete for new technology or invention in market. Internal
combustion engine is one type of automotive engine in which
fuel that run the mechanism is burned internally or burned
inside the engine cylinder. There are two types in internal
combustion engine which is reciprocating and rotary engine.
The type of engine that usually used is two stroke and four
stroke engine. In internal combustion engine, piston is one of
the important part defined as cylindrical component that
moves up and down in the cylinder bore by force produce
during the combustion process.
Crankshaft is a large component in an engine having
complex geometry that converts linear reciprocating
displacement of the piston to a rotary motion of the crank with
a four link mechanism. Since the crankshaft experiences a
large number of load cycles during its service life, its fatigue
performance and durability has to be considered in the design
process. Design developments have always been an important
issue in the crankshaft production industry, in order to
manufacture a less expensive component with minimum
weight, proper fatigue strength, higher fatigue life and
satisfying other functional requirements.
Since crankshaft is subjected to several forces which
vary in magnitude and direction (multiaxial). Connecting rod
transmitting gas pressure from cylinder to crankpin, the
stresses acting in the crankshaft vary with respect to time [5].
Most of time, crankshaft fails due to fatigue at fillet areas due
to bending load. Fillet rolling can increase fatigue life [6].
Engine mechanism and geometry has large impact on fillet
which experiences a large stress cycle during its working life.
Small crack initiates at this fillet location due to the stress
concentration which will propagate subsequently and failure
of crankshaft takes place[1]. Most of the crankshafts that
failed in fatigue were due to bending. Hence, fatigue Design
and Development has always an important issue in the
crankshaft production industry to manufacture less expensive
crankshaft with high fatigue strength [2].
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Crankshaft consists of the shaft parts which revolvein the main bearings, the crankpin to which the big end of the
connected rod is connected, the crank arms or webs (also
called cheeks) which connect the crankpin and the shaft parts.
The crankshaft main journal rotate in a set of supporting
bearings (main bearings) causing the offset road journals to
rotate in circular path around the main journal centers, the
diameter of that path is the engine stroke. Crankshaft must be
strong enough to take the downward force of the power stroke
without excessive bending. So, the reliability and life of the
internal combustion engine depend on the strength of the
crankshaft mainly. As the engine runs, power impulses hit the
crankshaft in one place and then another. The torsional
vibration appears when a power impulse hits a crankpin
toward the front of the engine and the power stroke ends. If
not controlled, it can break the crankshaft.
Reasons for the failure of crankshaft
i. Incorrect geometry leads to stress concentration.
ii. Crankpin material & its chemical composition
iii. Pressure acting on piston
iv. overloading on the engine
Table.1 Materials used in the analysis with properties
Stresses on crankshaft
Crankshaft experiences various stresses due to gas pressure
generated inside the cylinder by the combustion of air and
fuel mixture.The following two types of stresses are induced
in the crankshaft.
1.Bending stress
2.Shear stress due to torsional moment on the shaft.
The crankshaft is subjected to various forces but
generally needs to be analyzed in two positions. Firstly,
failure may occur at the position of maximum bending; this
may be at the centre of the crank or at either end. In such a
condition the failure is due to bending and the pressure in the
cylinder is maximal. Second, the crank may fail due to
twisting, so the connecting rod needs to be checked for shear
at the position of maximal twisting. The pressure at this
position is the maximal pressure, but only a fraction of
maximal pressure.
Fig.2 Various forces acting on a slider-crank mechanism
II. OBJECTIVE OF THE PROJECT
To analyze the stresses acting on the crankpin due to gas
force. Analyze the maximum deformation, maximum stress
point and dangerous areas of failure. Optimize the design to
reduce the weight of the component so that inertia effect can
be minimized.
III. METHODOLOGY
i. Measuring the dimensions of crankshaft
ii. Modeling the part in CATIA V5 software
iii. Importing the solid modal into ANSYS module
iv. Applying load and boundary conditions
v. Comparing the ANSYS results
vi. Optimization
IV. LITERATURE REVIEW
C M. Balamurgan et al [1]. He has been studied the
Computer aided Modelling and Optimization of crankshaft
and compared the fatigue performance of two competing
materials of crankshaft namely forged steel and ductile cast
iron. The 3D models of crankshaft were created by solid edge
software and then imported to ANSYS software. The
optimization process included geometry changes compatible
with the current engine, fillet rolling and results in increased
fatigue strength and reduced the cost and mass of the
crankshaft.
Abhishek Choubey and Jamin Brahmbhatt [2]. They
analyzed the 3D model of the crankshaft of diesel which were
created by SOLID WORKS Software and imported to
ANSYS software. In the crankshaft maximum deformation
was appeared at the centre of crankpin neck surface. The Sl
No.
Parameter Forged steel
Cast iron
Carbon steel
Gray Cast Iron
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Von-mises stress appears at the fillets between the crankshaftjournals and crank webs and near the central point journal.
The edge of main journal is the critical area as it is high stress
concentrated area.
R. J. Deshbhratar and Y.R Suple [3]. They were analyzed
the 4- cylinder crankshaft modeled in Pro/E Software and
imported into ANSYS software. Maximum deformation
appears at the centre of crankshaft surface. The maximum
stress appears at the fillets between the crankshaft journal and
crank cheeks, and near the central point. The edge of main
journal is the high stress concentrated area. The crankshaft
deformation was mainly bending deformation under the
lower frequency. And the maximum deformation was located
at the link between main bearing journal and crankpin and
crank cheeks.
Ling et al. [4]. They conducted the fatigue life prediction
of the model and residue life assessment based on statistics of
historical working state (SHWS) at crankshaft using fatigue
damage accumulation (FDA) theory. Dynamic response of
typical operation performance is analyzed with software
ANSYS. And high stress zone was found. Then, via rain flow
cycle counting to obtain stress time history, together with
SHOP, fatigue load spectra of key parts are compiled. Finally,
FDA model is built up with nominal stress method and
residue life based on SHWS is predicted the crankshafts of
diesel engine. It was found that main shaft journal of
crankshaft near the power output side and connected rod
journal have relatively high stress, and FDA of the same time
is relatively larger.
Applied load and boundary conditions
A normal pressure of 11 MPa with factor of safety 1.5 is
applied on the component when the crank is at the position of
maximum bending moment or is at the dead centre. Load data
were taken from the experiment conducted on the Kirlosker
TV1 engine in our college energy conversion laboratory.
The two main journal areas are fixed in the analysis according
to the real condition of the part in the engine. This constitute
a fixed boundary condition in our static analysis. Boundary
conditions applied here represents the actual running
condition of the engine using engine performance data i.e. the
pressure v/s crank angle curve.
Fig.3 Pressure vs crank angle plot
Table.2 Allowable bending and shear stress on Crankshaftt [7]
V. RESULT AND DISCUSSION
By the ANSYS WB14 analysis software got the results
like von-mises stress, maximum shear stress and total
deformation on crankshaft by applying load of 11 MPa
at the centre of crankpin when crankshaft is at dead
centre. The results obtained on 4 different material types
of crankshaft are compared for stresses, deformation and
mass. The material which has low density, induces low
stress and deformation on a crankshaft has been selected
as a suitable material in the analysis
Fig.4 2D view of the crankshaft model
Fig.5 Meshed model of the present crankshaft Material Endurance in
MPa
Allowable stress in MPa Bending Shear Bending Shear Chrome
nickel 525 290 130-175
72.5-97 Carbon
and cast steel
225 124 56-75 31-42
Alloy
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Fig.6 Applied load and boundary condition
Fig.7 Equivalent von-mises stress of 35.774 MPa
Modification to the present model
Results obtained from the present crankshaft are compared
one another and shows that there is a chance for reducing the
mass. Fillet of 5 mm radius has been applied on the less
critical sections as shown in fig. mass of about 65 grams has
been reduced. So, optimization in mass of the component has
been achieved.
Fig.8 2D view of the optimized model
Fig.9 Von-mises stress on optimized model of 33.059MPa
Forged
steel Cast iron
Carbon steel
Gray cast iron
present 26.025 30.079 28.351 35.774
optimized 35.362 32.526 30.341 33.059
26.0
25
30.0
79
28.3
51 35.7
74
35.3
62
32.5
26
30.3
41
33.0
59
90
Fig.10 Comparison of ANSYS results before and aftermodification
Optimization
By seeing all the results on present and modified model it was
possible to make mass optimization on the present model of
a diesel engine, applied the fillet (removing material) of
radius 5 mm at the edges of crankshaft. Fillet more than 5
mm, increases the stress on component beyond the allowable
limit. Von-mises stress and shear stress are increased by 3 to
4 MPa on each components. But, deformation and mass of the
component are decreased by considerable amount.
VI. CONCLUSION
Finally, by comparing all the determinants like
von-mises stress, shear stress, deformation and mass on all type
material crankshaft, Gray cast iron crankshaft is best suitable
from the study. Since, all the determinants are within safe
limit and mass of the Gray cast iron crankshaft is about
9.0277 kg which is lesser amongst different material
crankshafts. For the present modal, fillet of 5 mm radius has
been applied and 64 grams of material is reduced. Even
though, all the determinants are within the allowable limit. By
considering the inertia effect of crankshaft in the engine, Gray
cast iron crankshaft will impose less inertia effect.
REFERENCES
[1] C.M Balamurugan, R. Krishnaraj, Dr. M. Sakhivel, K.
Kanthavel, Deepan Marudachalam M.G, R. Palani.
“Computer Aided modeling and optimization of Crankshaft”,
International Journal of scientific and Engineering Research,
Vol-2, issue-8, ISSN:2229-5518, August-2011.
[2] Abhishekchoubey, JaminBrahmbhatt, “Design and
Analysis of Crankshaft for single cylinder 4-stroke engine”,
International Journal of Advanced Engineering Reaserch and
studies, vol-1, issue-4, ISSN: 2249-8974, pages: 88-90,
July-sept 2012.
[3] R.J Deshbhratar, Y.R Suple, “Analysis and optimization of crankshaft using FEM”, International Journal of Modern
Engineering Research, vol-2, issue-5, ISSN: 2249-6645,
Pages: 3086-3088, sept-oct 2012.
[4] S. Ai-ling, Y. Wen-hua, D. Zhou, L. Yu-mei,(2010),
“Assessment of Residue Fatigue Life of Crankshaft Based on Theory of Fatigue Damage” International Conference on
Optoelectronics and Image Processing.
[5] Jonathan Williams ana Ali Fatemi “fatigue performance
comparison and life prediction of Forged steel and ductile
cast iron crankshafts” 2007-01-1001
[6] RincleGarg, Sunil Baghla, “Finite element analysis and optimization of crankshaft”, International Journal of
Engineering and Management Reaserch, vol-2,Issue-6,ISSN:
2250-0758, Pages:26-31, December 2012
[7] R.S.Khurmi and J.K.Gupta, “A textbook of machine design by R.S.Khurmi and J.K.Gupta”
[8] Balaveereddi, “Design data hand book by Balaveereddi” Forged
steel Cast iron
Carbon steel
Gray cast iron
present 14.398 16.519 15.724 19.818
optimized 19.597 17.923 17.033 18.123
14.3 98 16.5 19 15.7 24 19.8 18 19.5 97 17.9 23 17.0 33 18.1 23
M A X S H E A R S T R E S S I N M P A
Forged
steel Cast iron
Carbon steel
Gray cast iron
present 0.00455 0.0056 5.1513 0.01057
optimized 0.004493 0.005581 5.0881 0.010459
0.00 455 0.00 56 5.15 13 0.01 057 0.00 4493 0.00 5581 5.08 81 0.01 0459
D E F O R M A T I O N I N M M
Forged
steel Cast iron
Carbon steel
Gray cast iron
present 9.1548 9.1548 9.9177 9.0277
optimized 9.0891 9.0891 9.8465 8.9628
9.15 48 9.15 48 9.91 77 9.02 77 9.08 91 9.08 91 9.84 65 8.96 28
