Question

A steel alloy is subjected to cyclic stresses and tested until failure. The results for different stresses are in Table 1. Use a graphical program to produce the S-N curve. (a) Determine the fatigue strength at 1 million cycles. (b) Determine the fatigue life for 400 MPa and for 200 MPa.

Table 1.

Stress (MPa) 475 435 390 350 310 308 305
Cycles to Failure 1x10^4 3x10^4 1x10^5 3x10^5 1x10^6 1x10^7 1x10^9

Answer 1

here two graph are there first is for finding values and second is whole graph as in whole data graph finding small value is not possible

(1) from 1st fatigue life for 1 mil cycle is 310 Mpa

(2) from chart cycle for 400 Mpa = 80000 cycle

for 200 Mpa life is infinite as shown from data graph does not go below 305Mpa