Acoustic-emission analysis of the processes of deformation and damage

Change of acoustic emission parameters is observed upon a single static loading of a flat metal specimen with the brittle strain-sensitive coating deposited on the surface. The activity of acoustic emission signals (their energy, number, and frequency) was recorded as the time of tensile loading increased. It is shown that upon further loading to the ultimate strength in the region of small elastic and elastoplastic deformations comparable to the yield stress deformations, the dislocation mechanism of deformation is attributed to the processes occurring at nano and micro levels with the corresponding frequencies of acoustic emission signals. The development of local deformations at micro- and meso-levels should be accompanied by a different signal structure when microdefects occur, with larger amplitudes and lower frequencies. Presumably, this occurs during formation of mesobreaks at the grain boundaries and in zones of large dislocation clusters. In this case the number of high energy signals should decrease at simultaneous decrease of acoustic frequencies. When tensile tests are performed on relatively coarse-grained steels of high strength and low ductility, then sound effects can be recorded even by human ear. In addition to the traditional analysis of these parameters, acoustic emission spectra have been constructed for given loading intervals. With the use of new integral parameters of those spectra, the gen- eral patterns of changes in the spectra from the region of higher to lower frequencies with increasing number of signals are shown. This fact indicates to oncoming of dangerous damaged state as the stresses increase in the coated aluminum sample. The generalized parameters of spectrum changes are presented. This provides a possibility to study the indicated features of elastic and elastoplastic deformation using spectral methods and new integral diagnostic parameters.

loading, stress, damages, acoustic emission, spectral characteristics, dangerous state

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