Simulation Of Tensile Behavior And Ballistic Performance Of Nanostructured Metals With High Strength And Good Ductility

Due to their good mechanical properties,nanostructured(NS)materials have attracted much attention and thus have been expected to be widely used in many fields.The subjects in this dissertation are two kinds of NS metals,i.e.,the coarse-grained(CG)metals strengthened by nanotwinned(NT)regions and the bimodal NS metals.Here,the objective is to provide effective guidance for the design and fabrication of the two kinds of NS metals via the investigation on their tensile and ballistic performance.The approach here is numerical.Via the Johnson–Cook plasticity model and the Johnson–Cook failure criterion,the effects of the nanotwin volume fraction on the tensile and ballistic performance of CG metals,together with the effects of the shapes and distributions of CG inclusions on the strength and ductility of the bimodal NS metals,are studied.The results indicate that for the CG metals strengthened by NT regions,the volume fraction of NT regions has significant effects on their tensile and ballistic performance.In terms of the strength and ductility,the effect of twin spacing on the overall ductility always decreases as the volume fraction increases.At low volume fraction of NT regions,their shapes are found to have significant influence on the overall ductility.As the volume fraction increases,shape effects on the ductility are found to diminish even though the effects on the strength are enhanced.In terms of the ballistic performance,in general,a relatively small twin spacing and a moderate volume fraction of NT regions can achieve both excellent limit velocity and limit displacement.With the increase of the volume fraction of NT regions,the strength increases,while the ductility decreases simultaneously.The above phenomenon leads to a general trend of ballistic performance,in which both the limit displacement and the limit velocity decrease with increasing volume fraction of NT regions.For the bimodal NS metals,both the shape and distribution of CG inclusions significantly affect the overall ductility,while the former has more prominent effects than the latter.Generally,the spherical CG inclusions with a more uniform distribution can achieve the best toughening effect.It is believed that the results of this dissertation provide important clues to the optimized strength,ductility,and ballistic performance of these two kinds of NS metals.