An axle is a dual-purpose component which supports the weight of the vehicle and drives the wheels.

There are 3 types of axles:

• Semi-Floating

• Three-Quarter Floating

• Fully Floating

We chose a Semi-Floating

axle because it is the most

widely used one.

Analysis

First we found out the various stresses acting on the axle shaft.

Those are:-

• Shear stress due to weight of vehicle

• Torsional stress due to driving torque

• Bending stress due to weight of vehicle (When shaft is subjected to pure bending)

• Tensile and Compressive stress due to cornering forces

The material we used for our shaft is C40 which has a

Maximum Tensile Stress = 640 N/mm2 = U

Maximum Shear Strength = 320 N/mm2 = S

R < U/3 and R’ < S/3 for safety.

We took Factor of Safety as 3.

Topic:- Design of a Rear Axle of a Car.

We designed our axle for 785kg, 5 seater OMNI car with a rear track width 119cm as our reference. The total weight comes up to 1185kg when considering the weight of 5 people. It has a wheel diameter of 20".

**DESIGN OF REAR AXLE OF A CAR**

INTRODUCTION

For finding the maximum stress on the shaft we used ‘The Maximum Shear Stress Theory’ and ‘The Maximum Principle Stress Theory’.

The resultant stress calculated from maximum principle stress theory is R and the resultant stress from maximum shear stress theory is R’.

Calculations

Data known to us:-

Total weight of car = 11850 N

Weight on each rear tyre = 2370 N,

Length of axle half shaft, l = .5334mm

Bending moment, M = W*l = 11850*.5334 = 1264.16 Nm

The Bending stress

B = 32*M/3.14*d3 = 12888.96/d3 N/m2

Bending Stress Calculation

The Tortional shear stress

T = (16*C*W*r)/3.1415d3 = 110.32/d3 N/m2

The Tortional Shear Stress

By maximum principal stress theory we calculate resultant R

R = B/2 + ((B/2)2 + T2)1/2 = 12889.91/d3 N/m2

By maximum shear stress theory we calculate resultant R’

R’ = ((B/2)2 + T2)1/2 = 6445.42/d3 N/m2

U/3 > R

640/3 = 12889.91/d3

d = 39.2 mm

and S/3 > R’

320/3 = 6445.42/ d3

d = 39.2 mm

From R40 series we take d = 40.5 mm.

For calculating diameter:-

Theory

Comparison with Actual Design

Calculated axle diameter: 40.5mm

Actual axle diameter: 35mm

Why is it different??

Thank You

Team Members:-

Ananthapadmanaban

Arun Babu

Krishnamohan C

Sayooj A.P

Shamim Akhtar

We chose C40 as the material and a

FOS of 3.

With reverse calculations using

d = 35mm we got the resultant stresses

as 300Mpa and 150Mpa.

To make it safe we decided to take the

material as AISI 1045/AISI 1141 Medium Carbon Steel.

AISI 1045 steel is a medium tensile steel supplied in the black hot rolled or normalized condition. It has a tensile strength of 600 - 800 MPa and Brinell hardness ranging between 170 and 210.

Chemical Composition:-

Carbon, C 0.420 - 0.50 %

Iron, Fe 98.51 - 98.98 %

Manganese, Mn 0.60 - 0.90 %

Phosphorous, P ≤ 0.040 %

Sulfur, S ≤ 0.050 %