Here attention was focused on the iron α − ε phase transformation. ![]() Thus, time-resolved measurement of these singularities and their comparison with a theoretical model prediction should give insight into the different physical process that govern the dynamic behaviour. These phenomena will usually correspond to singularities in the temporal profile of the target rear surface velocity. In some cases, further compression can induce a solid-solid (polymorphic) phase transformation or melting. ![]() Beyond some critical state of stress, the crystal defects, amplify and propagate through the lattice leading to plastic deformation, that can be caused by dislocation slip or twinning. The crystal generally begins to deform elastically along the direction of wave propagation with the lattice coming back to its original configuration on unloading. Besides, in all practical applications mentioned above, laser compression starts with a finite rise time, typically a few ns, before steepening into a shock wave after propagation over some distance from the irradiated surface, so that the superficial zone of interest is actually subjected to ramp compression.įigure 1 illustrates the dynamical response of polymorphic crystal material such as iron under laser ramp compression. Ramp compression is preferred to shock compression because it provides a better insight into the kinetics of the governing processes. In this article, we use laser driven ramp loading to investigate the effects of elastic-plastic behavior and allotropic phase transition (from α, bcc to ε, hcp) on wave propagation in iron. In such highly dynamic regime, time dependence, viscoplasticity and kinetic effects may play crucial roles. In order to optimize those processes and analyze their effects, physically based simulations are required to describe wave propagation from the loaded surface, subsequent pressure decay, plastically-affected depth, polymorphic transformations etc. A third example of industrial interest is the LAser Shock Adhesion Test (LASAT), which can be used to investigate debonding at a substrate-coating interface. Another one is laser shock-induced permanent compaction of porous materials such as sintered steels, over a few hundreds of μm below the loaded surface, to improve their mechanical properties. ![]() A successful engineering application is laser shot peening, leading to strain hardening and compressive residual stresses that have been shown to significantly enhance metals resistance to fatigue and corrosion. High power pulsed lasers offer means to subject materials to pressure loads of short duration, typically some ns to some tens of ns.
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