Question

A rotating beam test specimen when loaded to a stress of 900 MPa gives a life of 1000 load cycles. When loaded to 500 MPa, it withstands ${10}^6$ cycles. If the required life of the component is 50,000 cycles, what is the maximum stress it can be loaded?

Answer 1

${\sigma }_1=900MPa$,

${\sigma }_2=500MPa$,

$N_1=1000$,

$N_2={10}^6$

Plotting the two points on log-log curve

Eq. of straight line :

$\Rightarrow \text{log}\sigma -\text{log}900=\frac{\text{log}900-\text{log}500}{3-6}(\text{log}N-3)$

For N = 50000

$\sigma =645MPa$