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Design optimization of connecting rod
in heavy commercial vehicles
By R.AravindhanM.E CAD/CAM, CIPET Chennai
Internal Guide
Mr.E.Madhan Manohar,
Technical officer, CIPET Chennai
External Guide
Mr. Ashok kumar.B,
Sr.Manager, Adv Engg, Ashok Leyland, VVC
Dr. S. Sandesh.
Sr.Manager, Adv Engg, Ashok Leyland, VVC
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The objective of this project is to optimize and to reduce the weight of an automotive
connecting rod.
As existing connecting rod which is made of forged steel is over designed and bulky,
Austempered Ductile Iron (ADI) is chosen to replace forged steel.
Forces acting on the connecting rod were studied using Analytical method and compared with
ADAMS using CAD model.
Static and Fatigue analysis is done and compared with existing forged steel and proposed ADI
material on existing connecting rod design.
The design is then optimized using OPTISTRUCT solver for several iterations until achieving
the convergence.
The optimized designs were compared with existing connecting rod and the better design is
chosen based on stress, displacement.
OBJECTIVE
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LOADS ACTING ON CONNECTING ROD
LITERATURE REVIEW
Pravardhan Shenoy [1], a study was done to explore weight and cost reduction opportunities
for a production forged steel connecting rod. Here the tensile load acting on surface area is taken
as distributed over 180 degrees and compression force over 120 degrees.
Tensile load acting over 180 Compressive load acting over 120
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LITERATURE REVIEW
1. Constrain the crank pin end for all degrees of freedom of the connecting rod and applying
compressive force distributed over 120 in piton pin.
2. Constrain the piston pin end for all degrees of freedom of the connecting rod and
applying load at crank pin end over 120.
3. Constrain the piston pin end for all degrees of freedom and applying tensile load at 180
at crank pin end.
4. Bolt pretension force applied on beam element to equalize the bolt tightening torque and
the bush pressure is given in small end of connecting rod.
Three load cases were observed Vijayaraja [2] for FEA analysis of connecting rod.
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LITERATURE REVIEW
OPTIMIZATION
The basic principle of optimization is to find the best possible solution under given
circumstances.
Structural optimization is one application of optimization. Anton Olason[3] has done an
extensive work in optimization techniques. The type of optimization is basically branched into
three types - Size optimization, Shape optimization, Topology optimization.
sizing optimization Shape optimization
Topology optimization
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HEAT TREATMENT OF ADI [4]
ADI is produced by an isothermal heat
treatment known as Austempering.
First step is heating the casting to
austenitizing temperature in the range of
815-927 C
Then holding the part at austenitizing
temperature to get the entire part to
temperature and to saturate the austenite
with carbon
Quenching the part rapidly enough to
avoid formation of pearlite.
Austempering the part at the desired
temperature to produce a matrix of
ausferrite
LITERATURE REVIEW
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This table shows a clear picture of mechanical properties of ADI and compared to forged steel[4].
MECHANICAL PROPERTIES OF ADI
LITERATURE REVIEW
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Relative cost of ADI per unit
yield strength
Relative weight per unit yield strength
LITERATURE REVIEW
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ALLOYING ELEMENTS OF ADI
Carbon - Carbon in the range 3 to 4% increases the tensile strength but has negligible effect on
elongation and hardness. Carbon should be controlled within the range 3.6-3.8% except when
deviations are required to provide a defect-free casting.
Silicon - Silicon is one of the most important elements in ADI. It promotes graphite formation
and decreases the solubility of carbon in austenite. Increasing the silicon content increases the
impact strength of ADI and lowers the ductile-brittle transition temperature. Silicon should be
controlled closely within the range 2.4-2.8%.
ManganeseIt increases hardenability, but during solidification it segregates to cell boundaries
where it forms carbides and retards the austempering reaction. As a result, for castings with either
low nodule counts or section sizes greater than 19mm, manganese segregation at cell boundaries
can be sufficiently high to produce shrinkage, carbides and unstable austenite.
Information source [4]
LITERATURE REVIEW
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CopperCopper increases hardenability in ADI when added up to 0.8%. Copper has nosignificant effect on tensile properties but increases ductility at austempering temperatures below
350oC.
Nickel - Nickel can be added to ADI up to 2% to increase the hardenability. For austempering
temperatures below 350o
C nickel reduces tensile strength slightly but increases ductility andfracture toughness.
Molybdenum - Molybdenum is a hardenability agent in ADI, and may be required in heavy
section castings to prevent the formation of pearlite. However, both tensile strength and ductility
decrease as the molybdenum content is increased beyond that required for hardenability.
LITERATURE REVIEW
Information source [4
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I - Beam
Rod Small End
Rod Cap
Rod Bushing
Rod Bolt
PARTS OF CONNECTING ROD
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Engine specification
HINO BS 3 Engine
Engine type6 cylinder Inline engine
Peak pressure - 120bar
Maximum speed3250 rpm
Weight of connecting rod1.721 kg
Cylinder bore104 mm
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DYNAMIC LOAD ANALYSIS
INERTIA FORCES ACTING ON CONNECTING ROD [5]
Force acting on connecting rod crank end
FA = -mAaA
FA = mAr 2 (cos t + sin t )
Force acting on connecting rod at piston endFB = -mBaB
FB = mBr 2(cos t + cos 2t)
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ADAMS Simulation Model
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Crank
angle
(deg)
Acceleration
at B(m/sec2)
FB (manual calc)
(N)
Acceleration
at A (m/sec2)
FA (manual calc)
(N)
FB (ADAMS)
(N)
FA (ADAMS)
(N)
0 8581.68 14811.095 -6544.43 -18253.15333 14959.21 -18435.68
30 6686.27 11539.81 -8939.87 -24934.27 11655.21 -25183.61
90 -2037.25 -3516.08 -6544.44 -18253.15 -3551.24 -18435.68
143 -4665.08 -8051.44 1288.08 3592.59 -8131.95 3628.52
180 -4507.19 -7778.94 6544.44 18253.15 -7856.73 18435.68
225 -4627.62 -7986.78 9255.23 25813.86 -8066.65 26072.00
270 -2037.25 -3516.08 6544.44 18253.15 -3551.24 18435.68
360 8581.69 14811.10 -6544.44 -18253.15 14959.21 -18435.68
585 -4627.61 -7986.78 9255.23 25813.85 -8066.65 26071.99
700 7710.38 13307.32 -3911.43 -10909.41 13440.39 -11018.50
COMPARISON OF RESULTS WITH ADAMS
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Maximum Tensile forceAt piston end 14631.7 N
At crank end 25830 N
Maximum compressive force
At piston and crank end 101938 N
Bush pressure - 8.7 Mpa
Bolt pretension
25000 N
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FINITE ELEMENT ANALYSIS
Loads and Boundary conditions
For static analysis maximum compressive load due to gas pressure and maximum tensile load
due to inertia force is taken.
Bolt pretension is taken from the manufacturing manual[6].
Bush pressure due to interference is given in small end of connecting rod.
The mesh convergence analysis is performed to select the best element size for the analysis.
Static linear analysis is done for connecting rod because connecting rod works under elastic
limit.
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Finite Element Model of connecting rod with different load cases.
Compressive load
Tensile load
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DISPLACEMENT ON EXISTING CONNECTING ROD
Displacement due to
compressive load
Displacement due to
Tensile load
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Von mises stress distribution on existing connecting rod
Stress due to
compressive load
Stress due to Tensile
load
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Fatigue life of existing connecting rod
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Optimization
The aim of optimization was to minimize the mass of the connecting rod under the effect of a
load comprising the peak compressive gas load.
The scope of optimization is limited to the shank of connecting rod.
Big end and small end of connecting rod cannot be changed, as it cannot be used with existing
crankshaft and piston.
Design space
Non design space
RESULTS AND DISCUSSION
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RESULTS AND DISCUSSION
Topology optimization approach is used for optimization of connecting rod.
The optimization is carried out using OPTISTRUCT solver.
Several iterations with different objectives are taken to get many design models
Best three models are taken for comparison to choose the better one by considering the stress
results, displacement, fatigue and natural frequency.
RESULTS AND DISCUSSION
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Objective Min compliance
Constraint volume fraction .7
Objective Min max stress
Constraint volume fraction .7
Objective Min compliance
Constraint volume fraction .7
DESIGN I DESIGN II DESIGN III
RESULTS AND DISCUSSION
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Stress Distribution due to compressive force on optimized models
Design I Design II Design III
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Displacement due to compressive force on optimized models
Design IIIDesign IIDesign I
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Design I Design II Design III
Fatigue life of optimized models
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By comparing the three designs it is understood that design II is better compared to other
two.
In design I though the mass reduction is 15%, stress is high and fatigue life is very less. In design III the mass reduction is 13.5% and natural frequency of 1 st mode is high. But stress
is high.
Among the three design, Design II is having nominal stress and fatigue life is high.
Thus design II is selected, which has a mass reduction of 14%
Buckling factor for the Design II is 2
Buckling
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PropertiesExisting conrod
(forged steel)
Optimized connecting rod
(Austempered Ductile Iron)
Design I Design II Design III
Mass (grams) 1721 1468 1480 1493
Displacement (mm) 0.18 0.22 .20 .23
Maximum stress
(Mpa)320 470 406.1 521.2
Yield Strength
(Mpa)600 830 830 830
Tensile Strength
(Mpa)
790 1100 1100 1100
Fatigue Life
(cycles)108 105 107 106
Reduction in % 15% 14% 13.5%
Natural frequency
(Hz)562.8 455.5 526.8 535.5
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CONCLUSION
Thus the Design II with 14% weight reduction is chosen.
The Austempered ductile material can be used instead of Forged steel
FUTURE WORK
A prototype model is to be made and testing is done.
Fatigue analysis is done
It is tested by running it in engine for 240 hrs, for endurance
test
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References
1. Pravardhan S.Shenoy, 2004, Dynamic Load Analysis and Optimization of Connecting Rod.2. Vijayaraja et al ,AVTEC Ltd, Finite Element Analysis of Critical Components of the 2.6L
Gasoline Engine.
3. Anton Olason, 2010, Methodology for Topology and Shape Optimization in the Design
Process.
4. Ductile Iron data for design engineer, section IV, http://www.ductile.org/, updated on
25.7.2011, revised by J. R. Keough.
5. Robert Norton, 2ndedition, Design of Machinery.
6. Ashok leyland , Manufacturing manual.
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