Far-field initial response of acoustic emission from cracking in a weldment

An analytical expression is developed for the relationship between far-field acoustic emission (AE) signal and the propagation of a finite plane crack due to a nonuniform residual stress in a weldment. The AE sensor is situated at the boundary parallel to the crack surface. The quasi-static crack opening displacement (COD) rate is used as the source function. The AE initial response on a traction-free surface is obtained as a function of instantaneous crack length and speed. A closed-form expression is obtained for the normal surface displacement at the epicenter when the crack propagates at uniform speed for a finite duration between initiation and arrest. Results from an earlier analysis of the (variable) speed of crack propagation in a weldment are used to develop a more exact numerical prediction of the surface motion. The effects of initial crack length and bluntness on AE surface motion are investigated in both time and frequency domains.