Initiation and growth of damage in a dual-phase steel observed by X-ray microtomography

In situ tensile tests have been carried out on a high-strength, dual-phase steel. These experiments show that it is possible to follow and quantify the evolution of damage nondestructively and in three dimensions in this type of material. The measurements were analyzed in terms of density, size, aspect ratio of the cavities but also of the local deformation and the stress triaxiality in the sample. It was found that damage initiation is progressive with the applied tensile strain and that the initiation of new small cavities reduces the average diameter while the growth of the previously created ones increases the average diameter. This information was used to develop a new model for void growth based on the classical Rice and Tracey approach. This simple approach was modified to account for progressive damage initiation. The results of the proposed model are in good agreement with the measurements.