APPLICATION OFDesign and Analysis of a Connecting Rod

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DESIGN OF A CONNECTING ROD

• Connection between piston (gudgeon) pin and crank pin

• Converts linear motion to rotary motion

• Subjected to alternating compressive load

• Designed as a short strut against buckling using Rankine’s Formula

According to Rankine’s formula :• Wcr about x-axis = [for both ends hinged, l = L]• Wcr about y-axis = [for both ends fixed, l = L/2]

• For a connecting rod equally strong about both axes, the buckling loads must be equal. i.e.,

Ixx = 4 x Iyy [∴ = ×𝐼 𝐴 𝐾2 ]

Generally, Ixx = 3 to 3.5 times Iyy, and the connecting rod is designed to buckle in X direction.

X

X’

Y

Y’

5t

4t

tIn this case, we get :Ixx = 3.2 x Iyy

I - SECTION

PROBLEM SPECIFICATIONHonda 250 cc Specifications:

• Liquid cooled, 4-stroke, single cylinder, DOHC

• Displacement : 249.67 cc• Bore x Stroke : 76mm x 55 mm• Maximum Power : 28.6 BHP@9000 rpm• Maximum Torque : 23 NM@7500 rpm

STEPS IN AN ANALYSIS

Pre -processing

• Material Assignment• Creating/Importing CAD Model• Meshing• Applying Loads and Fixtures

Solving• Choosing a solver• Setting Analysis Parameters (if any)

Post-processing

• Viewing results• Interpreting results

MATERIAL ASSIGNMENTMechanical Properties of Forged Steel

CAD MODELLING

Section of the Connecting Rod :• I – Section

• B x H = 12 x 15 mm• Thickness of web and flange = 3 mm

Piston End Crank EndInner Diameter = 16 mm Inner Diameter = 24 mmOuter Diameter = 24 mm Outer Diameter = 32 mm

Length of the connecting Rod = (2 x stroke length) = 110 mm

LOADS AND FIXTURES

According to the formula :

Power = ½ • Mean Effective Pressure = 1.14 Mpa

• Considering Maximum Gas Pressure (Pmax) = 2 MPa,

• Buckling Load = Maximum Gas Force (PmaxApiston) = 9 kN

• Thickness of Web and Flange is taken 3 mm

MESH GENERATION• Model is divided into ‘Finite

Elements’• Calculations are done at the nodes

Meshing

1-D

• Beams• Pipes• Columns

2-D

• Sheet Metal• Instrument

Panel

3-D

• Engine block

• Crankshaft

Tetra Penta Brick(Hex)Pyramid

MESHING• Tetra-meshing• Max. size = 1.8 mm

• Fine Mesh :• High Accuracy• More Time

• Coarse Mesh :• Low Accuracy• Less Time

STRESSES AND DEFORMATION

LINEAR BUCKLING• The connecting rod buckles along

X-X direction as expected.

FATIGUE TESTS• S-N Diagram is constructed

according to the formula :Sa = σf ’ (2Nf) b

= 1131 (Nf) -0.0711 (MPa)• Alternating Loading is tested

according to Goodman’s Theory• Min. Safety Factor = 2.44• Min. Life = 108 cycles

RESULTSSl. No.

Test Value

1. Equivalent Stress (von Mises) 252.2 MPa2. Max. Principal Stress 97.73 MPa3. Normal Stress (X-axis) -60.26 MPa4. Normal Stress (Y-axis) -222.36 MPa5. Normal Stress (Z-axis) 97.73 MPa6. Total Deformation 0.05 mm7. Fatigue Test : Safety Factor 2.448. Linear Buckling : Load

Multiplier5.598

!!! Thank You !!!