Microscopy of Fatigue Crack Arrest Behavior of Ferrite Steel

Abstract

In order to elucidate the influence of microstructure on the crack non-propagation behavior, I did fatigue crack propagation test with K-decreasing process to obtain the threshold stress intensity range ΔK_th. Then, I investigated the effect of crystal grain size on its value. As a result, it was found that the value of ΔK_th is substantially constant irrespective of crystal grain size. Also, I examined fatigue crack non-propagation behavior using slip factor. Just for information, slip factor is the resolved shear stress ratio calculated considering the singular stress field at the crack tip. Slip factor is calculated for each slip system, but even if the value of the slip factor is large, it was observed that the slip system did not happen and the crack did not propagate. Then, I focused on the distance from the crack tip to the grain boundary. As a result, it was found that cracks do not propagate as long as the slip factor is large but the distance from the crack tip to the grain boundary is small. Therefore, it was found that not only the slip factor but also the influence of grain boundary should be taken into consideration when studying fatigue crack non-propagation behavior.