Dynamic fracture of tantalum under extreme tensile stress

The understanding of fracture phenomena of a material at extremely high strain rates is a key issue for awide variety of scientific research ranging from applied science and technological developments to fundamental science such as lasermatter interaction and geology. Despite its interest, its study relies on a fine multiscale description, in between the atomic scale and macroscopic processes, so far only achievable by large-scale atomic simulations. Direct ultrafast realtime monitoring of dynamic fracture ( spallation) at the atomic lattice scale with picosecond time resolution was beyond the reach of experimental techniques. We show that the coupling between a high-power optical laser pump pulse and a femtosecond x-ray probe pulse generated by an x-ray free electron laser allows detection of the lattice dynamics in a tantalumfoil at an ultrahigh strain rate of epsilon similar to 2 x 10(8) to 3.5 x 10(8) s(-1). A maximal density drop of 8 to 10%, associatedwith the onset of spallation at a spall strength of similar to 17 GPa, was directlymeasured using x-ray diffraction. The experimental results of density evolution agree well with large-scale atomistic simulations of shock wave propagation and fracture of the sample. Our experimental technique opens a new pathway to the investigation of ultrahigh strain-rate phenomena in materials at the atomic scale, including high-speed crack dynamics and stress-induced solid-solid phase transitions.