Question

A steel rotating-beam test specimen has an ultimate strength of 210 kpsi. Estimate the fatigue strength corresponding to a life of 200,000 cycles of stress reversal.

Answer 1

Solution:- The given problem has been solved using the standard formulas and principles used in the subject of Mechanical engineering design. Standard data from standard textbooks were followed to solve the given problem.

Solution: Given dator : ultimate strength of the specimen Sut = 210kpsi of cycles of stress-rew Number N = 200,000 we will whese As Sut > 200kpsi, so take se - 100KPSE se = endurance limit of the test specimen Also we have Se= =se? (For this case) where se = endurance limit of the actual machine part Now from the standard dater figure of Fertigue strength factor ultimate strength and 1 we

the value factor (f) of fatigue strength Conselponding Sut = 210 kpsi Ito af! F = 0.775 a Nb Now the fatigue strength can be given by : Sf are the constants are given by :- (f Sut) ² where which a and b a= Se

and b= -1 log (f Sut (0.775 X 210) (10o 2 So, a a= 264.88 kpsi and b = I log log (0.7754.210 3 b = 0.0705 Now the stre fatigue given as: rength can be again

SF a N 0.0705) SF = 264.8e) (200,000) 1 Sf 112 KPsi And