Acoustic Emission Analysis of Deformation and Damage Processes

Аннотация

The change in acoustic emission parameters is observed upon a single static loading of a flat metal specimen coated with a brittle strain-sensitive coating. The acoustic emission signal activity (energy, number, and frequency) was recorded as the tensile loading time increased. The dislocation mechanism of deformation in the area of small elastic and elastoplastic deformations, being commensurate with yield stress deformations at further loading to the ultimate strength, is shown to be induced by the processes that occur at the nano- and micro-levels with the appropriate acoustic emission signal frequencies. On the other hand, the evolution of local deformations with the emergence of defects at the micro- and mesoscales should be accompanied by different signal structures with higher amplitudes and lower frequencies. This is likely due to the formation of mesocracks at the grain boundaries and dislocation cluster rich zones. In this case, the number of high energy signals is expected to decrease at simultaneously decreasing acoustic frequencies. When tensile tests are performed on relatively coarse grained steels of high strength and low ductility, the sound effects can be heard even by the human ear. In addition to the traditional analysis of these parameters, the acoustic emission spectra have been plotted for specified loading intervals. Using new integral parameters of those spectra, the general regularities of spectral changes from the region of higher to lower frequencies are shown with increasing number of signals. This fact indicates the oncoming of hazardous damaged states caused by stress propagation through a coated aluminum sample. The generalized parameters of spectral changes are given as well. This allows the indicated elastic and elastoplastic deformation features to be characterized by means of spectral tools and new integral diagnostic parameters.