Dans les matériaux fragiles, la mécanique linéaire élastique de la rupture (MLER) préditune énergie de fracture constante et une vitesse de fissuration limitée par la vitesse deRayleigh (CR). Or un grand nombre d’expériences contredisentces prédictions. Pour comprendre ce désaccord, nous avons développé un dispositif derupture dynamique dans un matériau fragile modèle – le PMMA. Nous montrons l’existenced’une divergence de l’énergie de fracture à 0,2 CR due à unetransition fragile/quasi-fragile. Nous suggérons qu’un modèle géométrique pourra aider àmieux comprendre la dynamique de propagation et d’endommagement.

The approach to the ultimate strength of metals is determined experimentally. The strength of the materials and the strain rate were determined from the free surface velocity time history, which was measured with an optically recording velocity interferometer system. The dynamic strength was measured at strain rates in the domain of 5·106 to 5·108 s−1. The necessary tension to break the metal (spall) and the very high strain rates were achieved using high-powered lasers in nanosecond and picosecond regimes. The measurements at strain rates larger than 108 s−1 were achieved for the first time. The ultimate strength of metals was calculated using a realistic wide-range equation of state. Our experiments indicate that under very fast tension processes, the dynamic strength of materials is determined not by the macroscopic defects but by atomic quantum mechanical processes described by the equation of state of the material. The rate of the process is described by the strain rate, and at strain rates higher than 5·107 s−1, the atomic forces are dominating the dynamic strength of materials.

Dynamic propagation of a crack along the interface in an anisotropic material subjected to remote uniform anti-plane shear is studied. The crack is assumed to nucleate from an infinitesimal microcrack and expands with a constant velocity. Explicit expressions for the stress intensity factor and the energy release rate are derived.