DESIGN AND FATIGUE ANALYSIS OF METAL MATRIX COMPOSITE CONNECTING ROD USING

FEA

Submitted by

NITHIL.G, SARAVANAN.C

III-Year Mechanical DeptMother Teresa Collage of Engg and Tech, Pudukottai

Abstract

Composite materials are now a day widely used in engineering field

The objective of the project is to design and fatigue analysis of the metal

matrix composites (MMC) connecting rod

The connecting rods are commonly used in the internal combustion engines

and are subjected to millions of varying stress cycles loading to fatigue failure

In that project both the standard steel and composite connecting rods are

modeled and analyzed using solid works 2010 and cosmos software

IntroductionConnecting Rod

Connecting rod is an intermediate member between the piston and the

crankshaft

Its primary function is to transmit the push and pull from the piston pin to

the crank pin and thus converts the reciprocating motion of the piston into

the rotary motion of the crank

It consists of a long shank a small end and a big end. The cross section of

the shank may be rectangular, circular, tubular “ I section and H section”.

Generally circular sections are used for low speed engines where I section

is preferred for high-speed engines.

Forces Acting On Connecting Rod

Force on the piston due to gas pressure and inertia of the reciprocating

parts

Force due to inertia of the connecting rod or inertia bending forces

Force due to friction of the piston rings and of the piston

Forces due to friction of the piston pin bearing and crank pin bearings.

The Development Objectives For Light Metal Composite Materials

Increase in yield strength and tensile strength at room temperature and

above

While maintaining the minimum ductility or rather toughness,

Increase in creep resistance at higher temperatures compared to that of

conventional alloys,

Increase in fatigue strength especially at higher temperature,

Improvement of corrosion resistance,

Increase in young’s modulus,

Reduction of thermal elongation

Improvement of thermal shock resistance,

Mechanism Of Fatigue

A fatigue fracture always starts as a small crack which, under repeating

loading of stress grows in size.

As a crack expands, the load carrying cross-section of the metal component

is reduced, as a stress rises

The events that lead to fatigue include

1.crack nucleation

2.crack growth, and

3. fracture

STEPS INVOLVED IN FEA

PREPROCESSING

ANALYSIS

POSTPROCESSING

PREPROCESSING

..

Calculation

Specifications :

B.H.P = 7.6

Bore = 49 mm

Stroke = 56 mm

Crank Radius = 56/2 28 mm

Piston Diameter = 48.5 mm

Piston Weight = 65g (0.065 Kg)

After calculation load acting on the connecting rod

WB = 13020 N

Material Properties For Conventional Connecting Rod

Material name : Alloy steel

Elastic modulus : 210000 N/mm^2

Poisson's Ratio : 0.28

Density : 7700 Kg/m^3

Ultimate Tensile Strength : 723.83 N/mm^2

Thermal expansion : 1.3e-005 /k

specific heat : 460 j/kg k

Material Properties For Composite Connecting Rod

Material name : Alloy steel

Elastic modulus : 210000 N/mm^2

Poisson's Ratio : 0.28

Density : 7700 Kg/m^3

Ultimate Tensile Strength : 723.83 N/mm^2

Thermal expansion : 1.3e-005 /k

specific heat : 460 j/kg k

ANALYSIS

Software Used

Solid work for modeling and meshing,

Cosmos for analysis

Meshing In Solid Works

Displacement (mm) 0.05506

Maximum stress (vonmisses stress in Mpa) 0.624

Weight in grams 115.48

Result Output (Tension)

Tensile Analysis For Conventional Connecting Rod

Boundary condition :

Engine mounted vertically

Bottom end (Big end) – Fixed

Top end (small end) – application of load

Displacement (mm) 0.0373

Maximum stress (vonmisses stress in Mpa) 0.423

Weight in grams 72.17

Result Output (Tension)

Tensile Analysis For Composite Connecting Rod

Boundary condition :

Engine mounted vertically

Bottom end (Big end) – Fixed

Top end (small end) – application of load

21/07/11

Stress Conventional connecting rod

Composite connecting rod

Tensile stress (Mpa) 0.624 0.423

Life (Days) 76.71 302.69

Strength to weight ratio

Comparatively lesser Comparatively greater

Mass 115.48 grams 72.17 grams

Fatigue Analysis Comparison

RESULTS

STRESS ANALYSIS FOR CONVENTIONAL CONNECTING ROD

DISPLACEMENT – CONVENTIONAL CONNECTING ROD

STRESS ANALYSIS REPORT FOR COMPOSITE CONNECTING ROD

DISPLACEMENT RESULTS FOR COMPOSITE CONNECTING ROD

Conclusion

The conventional connecting rod used in the engines was replaced with a composite connecting rod

Stress induced in the composite connecting rod is found to be lower

then that of the conventional connecting rod

Number of working days for composite connecting rod is high

Composite connecting rod material is replaced for good fatigue

strength