Surface effect of acoustic anisotropy during plastic deformation of metals

The work is devoted to investigation of the surface effect of acoustic anisotropy detected in specimens cut from rolled aluminum sheet and destroyed after uniaxial inelastic tensile tests. It is caused by the collective influence of systems of microcracks localized in the surface layer of metal on the phase shift between velocities of orthogonally polarized bulk transverse waves. The removal of a thin 220 µm surface layer in a 20 mm thick aluminum specimen leads to a sevenfold change in the integral value of acoustic anisotropy. The dependence of the value of acoustic anisotropy on the thickness of the removed surface layer has a damped oscillating behavior. The method of angular diagrams of acoustic anisotropy is used to study the surface effect and residual plastic deformations. The weakening of the surface results in a qualitative change in the shape of angular diagrams of acoustic anisotropy. The obtained result can be applied to independent estimation of accumulated plastic deformations and damage in metals using acoustic anisotropy.