Evaluation of Service Load by Micro-Fractography of Fatigue Fracture

Abstract

Fatigue tests under a constant average load with load spectrum of conditional distribution, which resembles a usual service load in structural parts, were carried out on CT test specimens of stainless steel (SUS 304) and the striation spacings formed on the fracture surface were measured by micro-fractography.
As preliminary tests, five kinds of block loadings were applied to the test specimens, and the relationship between the applied load and striation spacings was investigated. Fatigue tests and fractography on two kinds of random loadings simulating a usual service load were then carried out, and the possibility to evaluate the random load by striation spacing measurements was examined. It is suggested that fractography is useful for evaluation of main service load spectrum responsible to fatigue crack growth.