Question

A shaft made of steel alloy ($S_{ut}$ = 820 MPa and Se = 280 MPa) is operated under fatigue loading condition. If the subjected alternative stress is 420 MPa, the number of cycles it will go before failure is

• A. 50000
• B. 55000
• C. 60000
• D. 55576

Answer 1

The correct option is D 55576


Since ABC is a straight line, so slope of AC = slope of BC

$\frac{log(0.9\times 820)-log\left(280\right)}{3-6}=\frac{log\left(420\right)-log\left(280\right)}{x-6}x=4.7448$

log N = 4.7448 $\Rightarrow$ N = 55576.32 cycles