Question

A component made of steel subjected to completely reversed bending stress. Ultimate stress = 700 MPa, yield stress = 450 MPa and fatigue strength is 200 MPa.

If the component is to withstand 75,000 cycles of load, the maximum stress that can be induced in the component is

• A. 307 MPa
• B. 400 MPa
• C. 185 MPa
• D. 350 MPa

Answer 1

The correct option is A 307 MPa

Given, $S_{ut}=700MPa$,

$S_y=450MPa$,

Se = 200 MPa

$0.9S_{ut}=700\times 0.9=630MPa$

Plotting on log-log curve :


Straight line equation is

$\Rightarrow \text{log}\sigma -\text{log}630=\frac{\text{log}630-\text{log}200}{3-6}(\text{log}N-3)$

$ForN=75000$

$\sigma =307MPa$