Effects of Lateral Plate Dimensions on Acoustic Emission Signals from Dipole Sources

With a validated three-dimensional finite element code, the out-of-plane displacements corresponding to model sources of acoustic emission (AE) were calculated in aluminum plate samples of two different lateral dimensions. Both samples were 4.7 mm thick. The lateral dimensions were 480 mm by 25.4 mm, which represented a laboratory-size coupon, versus 1000 mm by 1000 mm, which represented a larger field-size sample. The displacement signals were calculated for positions of the receiver on the top plate surface at several different distances (in the far-field) from the source’s epicenter. The signals were predicted for the same propagation distances of source-to-receiver in both the large and small samples. Models of both point-like sensors as well as sensors with a large aperture were used. The signals were filtered with either a 40-kHz high-pass filter or a 100-to-300-kHz bandpass filter. The AE sources were modeled as either a point single dipole (both in-plane and out-of-plane) or a point multi-dipole located at different depths within the plate thickness. Analysis of the simulated AE signals shows that the superposition of edge reflections on the arrivals of the direct signal significantly distorts and amplifies AE signals in the laboratory-size coupon relative to a larger field-sized sample. This results in significantly larger AE signal features such as amplitude, duration, and energy in the laboratory-sized sample. Edge reflections also distort the frequency spectrum of signals in the small sample.