Laser shock peening (LSP) can be used to induce compressive residual stresses on the surface of a material, then to improve the mechanical properties such as performance of plasticity and fatigue. However, the residual stresses and their exact spatial distribution are very difficult to measure by experiment, especially for very small workpieces. In this paper, a finite-element model has been developed to numerically simulate the LSP process of bulk metallic glass (BMG) Zr41.2 Ti13.8Cu12.5Ni10Be22.5, and predict the stress distribution. The constitutive equation established in this work is hydrostatic-pressure sensitive and strain-rate dependent, it is based on the free volume model and Coulomb-Mohr yield criterion, and can describe such special deformation behaviors of BMG as strain softening. The simulated results show that, for one-side peening, along depth direction, the compressive residual stress gradually reduced to zero, then change to the tensile residual stress, but for two-side peening, the residual stress is from compressive to tensile and then to compressive along depth direction. These simulation results have a great significance to study the application of LSP in strengthening brittle amorphous alloys.
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 process can serve as a rapidly established and high precision technique to impress micro features on thin sheet metals. The response of brass foil under different ratio of laser beam diameter (d) to die hole diameter (D) in micro scale laser shock punching was investigated. The typical fracture surface morphologies were observed using scanning electron microscope. The influence of the ratio d/D on dynamic deformation and fracture of the brass foil was characterized. The results show that the dynamic fracture behavior of the brass foil is sensitive to the ratio d/D. According to the general mechanical analysis, the specimen fails in a shear fracture mode at d/D=1.75 due to the existence of shear stresses, while the fracture occurs in a tensile fracture mode at d/D=0.47 under the effect of bidirectional tensile stresses. In the case of d/D=0.70, the specimen fails in a mixed fracture mode under the co-action of tensile and shear stresses.