design optimization of conrod by r.aravindhan

8/2/2019 Design Optimization of Conrod by R.aravindhan

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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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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.



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Objective Min compliance

Constraint volume fraction .7

Objective Min max stress


Objective Min compliance


DESIGN I DESIGN II DESIGN III



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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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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)


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.
http://www.ductile.org/http://www.ductile.org/


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design optimization of conrod by r.aravindhan

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