Creep damage modeling based on ultrasonic velocities in copper

We measured the ultrasonic velocities and the porosity for pure copper samples subjected to the intergranular creep process. The ultrasonic velocities decreased and their anisotropy developed as the creep advanced. We study a double composite model implied by photomicrographic observations and calculated the transversely isotropic effective stiffness. In this model, spherical voids arc uniformly distributed within oblate ellipsoidal volume elements. These ellipsoids are randomly embedded in an isotropic copper matrix with an axisymmetrical distribution of the minor axes around the stress direction. Incorporation of the unperturbed velocities, the porosity, and the ellipsoid aspect ratio into the modeling calculation provides the basis features of the damage morphology : the void volume fraction (in the ellipsoids) and the lowest-order expansion coefficients of the orientation distribution function (ODF). Comparison between the calculated and measured velocities was quite satisfactory, showing the validity of this micromechanical modeling. 0 1997 Elsevier Science Ltd. All rights reserved.