Dependence of acoustoelastic birefringence on plastic strains in a beam

Acoustoelastic birefringence is measured by transmitting ultrasonic shear waves at two perpendicular polarizations through the thickness of an aluminum beam. From the data obtained before bending, after bending, and after the beam has been sectioned to relieve the residual stresses, the acoustoelastic birefringence induced by residual stress is separated from that induced by texture change. Supplemented with strain-gauge data at all these states, the texture-induced anisotropy is shown to be related to plastic (permanent) strains in the beam. A nearly linear relationship is observed in compressional deformation of 6061-T6 aluminum up to −0.6% plastic strain in the beam, whereas the birefringence is almost independent of tensile plastic strain.