A progressive damage model for ultrasonic velocity change caused by creep voids in copper

In order to investigate the creep voids–ultrasonic velocity relationships and the associated modeling, a series of crept copper samples are prepared and their ultrasonic velocities are measured. Velocities measured in three directions with respect to the loading axis are found to decrease nonlinearly and their anisotropy increases as a function of creep-induced porosity. A progressive damage model is developed to explain the observed void–velocity relationship, including the anisotropic behavior. In the model study we assume the creep voids as oblate spheroids and the axisymmetric orientation distribution of their minor axes with respect to the loading direction. We further assume that the void aspect ratio can vary as the creep advances. This model enables the determination of the average aspect ratio of voids for a given porosity content and provides a satisfactory agreement with experimental results over the whole creep life.