Proposal for a New Threshold Stress Intensity Factor Range Equation for Fatigue Crack Propagation and a Study on the Analysis of Peculiar Fracture Behavior of Shot Peened Materials by its Application

Abstract

An equation of the threshold stress intensity factor range was proposed for the fatigue crack growth using a nonlinear region of unique fatigue fracture. The following phenomena, peculiar to the peening specimen with a pre-crack, were analyzed using previous experiment results based on the proposed equation. As a result, the following to phenomena could be evaluated quantitatively whereas was evaluated qualitatively. Pre-crack size that can be rendered harmless by peening; Fatigue limit of pre-crack specimen that cannot be rendered harmless; A phenomenon that fatigue fracture appears from outside the pre-cracked part on most of the harmless pre-crack specimen; Non-propagating crack condition of stage II (tensile type), observed in most specimen showing fatigue limit; and Qualitative analysis for initiation of non-propagating stage II crack (tensile type) in the peening specimen based on the reference regarding to a micro distribution of residual stress due to peening.