Peak Load in Rapid Compression Tests: Experiments and Micromechanical Modelling

Rapid compression tests are useful to characterize the semisolid behaviour in thixoforming conditions. The load-displacement curves typically display a peak load. The origin, the maximum value and the height of this peak are discussed comparing calculated results obtained using a micro-macro model and experimental data obtained in earlier work. As suggested by experiments, the calculated peak load originates from a 3D continuous solid skeleton, which breaks down under load. For the same initial semisolid structure, the model predicts that decreasing the ram speed decreases the maximum of the peak because of a strain rate effect. In addition, the peak load is found to be quite sensitive to initial internal structure, namely the volume fraction of entrapped liquid, which may change for various soaking times. Finally, the time for the solid skeleton breakdown is found to be in good agreement with experimental results.