FAILURE MECHANISMS OF LIGHT ALLOYS WITH A BIMODAL GRAIN SIZE DISTRIBUTION

Physical mechanisms of dynamic fracture of ultrafine-grained (UFG) light alloys were investigated by numerical simulation method. The multiscale level approach has been used for computer simulation of magnesium and aluminium alloys response to tension and compression at high strain rates. The model structured representative volumes (RVE) takes into account the influence of unimodal and bimodal grain size distributions and concentration of precipitates on mechanical properties of alloys. Fracture of fine-grained alloys under dynamic loading has probabilistic character and depends on parameters of structure heterogeneity. Damage nucleation is associated with strain localization at mesoscale level. Results of computer simulation demonstrate that the high strain localization in UFG alloys under dynamic loadings depends on the ratio between volume concentrations of small and coarse grains. Fine precipitates in alloys not only affect the hardening but also lead to change the influence of the grains size distribution on volume concentration of shear bands.