A Fatigue‐crack‐growth‐based Analysis of Two‐step Corrosion Fatigue Tests

Abstract

A method for the analysis of two-step fatigue level sequences is proposed and compared with experimental results. Two-step loading tests of the aluminum alloy 2017-T4 in 3% sodium chloride solution have been carried out in conjunction with a replica technique used to monitor the growth of fatigue cracks. Fatigue cracks were nucleated at corrosion pits 10-15 pm in size, and crack growth rather than crack initiation was found to take up the major portion of the fatigue lifetime in these tests. The results could therefore be analyzed on the basis of the following constitutive relation for fatigue crack growth This analysis was simplified since the influence of transients in the crack growth rate induced upon change in load level was found to be minimal. The approach provides a rational basis for dealing with load-sequence effects.

Influence of pitting on the fatigue life of a turbine blade steel

“…where Δ K th is the range of the threshold stress intensity factor, Δ σ th is the threshold fatigue strength, a is the pit depth and α is a geometry factor. For semicircular surface cracks, α is approximated by 0.67 30 –32 …”