Acoustic emission from strain-determined sources

Abstract

Monitoring of structures can be based on observing signals emitted in the course of developing defects. Layered ductile structures are considered which react on overloads by the formation of (small scale) plastic zones. Within the linear elastic background concept such an event is considered by the formation of sources of eigenstress. Since a direct description of the source characteristics is rather cumbersome, alternatively, the time convolution of the imposed plastic strains with the complementary Green’s stress dyadic is proposed to describe the signal of the acoustic emission. Thus, the dynamic generalization of Maysel’s formula of thermo-elasticity, a special form of the dynamic reciprocity theorem, enters the field of computational “nondestructive evaluation”. In that context, the novel contribution of this paper to acoustic emission and monitoring of structures is the formulation of the full three-dimensional problems and, for layered structures, the construction of the generalized rays (plane wave expansions) in the background, considering an instantaneous oblique force point source at the transducer’s location. Consequently, all information on the wave guide is contained in the Green’s stress dyadic. The Laplace transformed solution is worked out for localized plastic sources. Deconvolution and transducer dynamics is not discussed here.