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 ① to ④ phenomena could
be evaluated quantitatively whereas ⑤ was evaluated qualitatively. ①
Pre-crack size that can be rendered harmless by peening; ② Fatigue limit
of pre-crack specimen that cannot be rendered harmless; ③ A phenomenon
that fatigue fracture appears from outside the pre-cracked part on most
of the harmless pre-crack specimen; ④ Non-propagating crack condition of
stage II (tensile type), observed in most specimen showing fatigue
limit; and ⑤ 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.