DEPENDENCE OF AE PARAMETERS ON THE PROPAGATION DISTANCE
摘要
Acoustic emission (AE) technique is used to monitor the fracture process in engineering materials and structures. The pulse emitted during a cracking incidence depends on the motion of the crack tip and supplies information on the mode of active cracking. Therefore, AE data are used for classification of the dominant cracking mode. This is significant since nucleation of shear cracks generally follows tensile ones on an existing failure surface and crack characterization gives insight in the current stage of the fracture process. The differences in the microscopic motion of the crack sides for the distinct crack modes results in noticeable changes in the AE signals, concerning their shape and frequency content. However, due to inherent inhomogeneity of the materials the pulse is strongly distorted until reaching the AE sensor on the surface. This effect is accumulated with propagation distance and renders crack classification troublesome for large structures. In the present study, the Boundary Element Method (BEM) is employed and numerical simulations dealing with the propagation of AE signals generated by the loading of straight and inclined surface breaking cracks are conducted. This study includes both the generation of the pulse from a crack propagation incidence of a surface breaking crack and reception of the corresponding wave at several different positions. The relative motion of the crack sides is varied in order to simulate different crack modes, while different crack tip geometries are investigated. Waveform analysis reveals the strong dependence of AE parameters on the distance between the source crack and the receiving point, stressing out that the influence of distance is crucial and should be taken into account for successful cracking mode characterization.