Variation of fracture mode in micro-scale laser shock punching

Micro-scale laser shock punching is a high strain rate micro-forming method which uses the high-amplitude shock wave pressure induced by pulsed laser irradiation. The response of brass and pure titanium foils under the different ratio of laser beam diameter (d) to die hole diameter (D) in micro-scale laser shock punching was investigated experimentally and numerically. The typical fracture surface morphologies were observed using scanning electron microscope. Numerical simulations were conducted to predict the stress state of the workpiece before and after fracture. The influence of the ratio d/D on dynamic deformation and fracture of metal foils was characterized. The results demonstrate that both the crack locations and fracture surface morphologies of metal foils are strongly related to the ratio d/D. The fracture mode varies from a shear fracture mode to a mixed fracture mode, then to a tensile fracture mode as the ratio decreases. The stress state under the different ratio is discussed in detail and believed to be responsible for the variation. •Effect of the ratio of beam diameter (d) to die hole diameter (D) is studied.•The fracture mode of metal foils varies as the ratio d/D changes.•The crack location of metal foils is strongly related to the ratio d/D.•The stress state under the different ratios is simulated and discussed.