2010 Volume 51 Issue 7 Pages 1255-1263
Three acoustic techniques, namely longitudinal wave reflection, vertically-polarized shear wave (SV) reflection, and horizontally polarized shear wave (SH) transmission methods, were used to assess the cyclic-tension fatigue of an extruded pure magnesium. The acoustic velocities were measured by the reflection methods, and found to decrease considerably at the beginning of the fatigue. This suggests that void defects formed at grain boundaries (Coble creep). Decrease in the elastic moduli and increase in the internal frictions revealed decrease in the mechanical and increase in the viscoelastic properties during the fatigue progress, respectively. For SH transmission method, acoustic parameters such as propagation time, amplitude and logarithmic damping ratio were strongly affected by detouring of acoustic waves, accompanied by variation in the residual stress caused by acoustoelasticity, in comparison with the reflection methods. These acoustic results were determined using OM, SEM, Vickers hardness tester, surface roughness tester and XRD.
