Simulation Of Ballistic Performance And Fracture Behavior Of Two Novel Nanostructured Metals

Target-plate materials have attracted much attention in recent years because of their technological importance.Several kinds of structural materials including ceramics,Kevlar/epoxy composite,and carbon nanotube-based composites have been studied and optimized for target-plate applications.Additionly,nanostructured metals are also very appealing.In this desertation,focus is on the bimodal nanostructured Cu and the coarse-grained Cu strengthened by nanotwinned regions,and their ballistic performance and fracture behavior are studied.Nanostructured metals with bimodal grain size distribution have high strength,good ductility,and excellent ballistic performance.This work is based on the Johnson–Cook failure model.The influence of the distribution and shape of the coarse-grained inclusions on the ballistic performance of bimodal nanostructured Cu is studied.The effects of constitutive and failure parameters of the nanograined phase together with boundary constraint of the specimen are also investigated.The analysis shows that,to improve their ballistic performance,the coarse-grained inclusions need to have regular distribution and they also need to have a longer projection perpendicular to the direction of impact.The simulations show that when the abrasion effect is not considered,the ballistic performance of the microstructures depend heavily on their ductility.The results also show that when the constraint is released,the ballistic performance is reduced tremendously.In coarse-grained metals strengthened by nanotwin regions,the presence of the nanotwin regions contributes to their ultrahigh strength,while their good ductility is attributed to the recrystallized coarse grains.Here,numerical simulations based on the Johnson–Cook failure criterion are carried out to investigate the effects of twin spacing and microstructural attributes on their ballistic performance.It is found that smaller twin spacing and regular distribution of nanotwin regions are helpful to the promotion of the ballistic performance.It is also found that the role of the shape of nanotwin regions is significantly affected by twin spacing.It is found that microstructures with array arrangement of nanotwin regions have higher limit velocities and smaller relative displacements than the single phase coarse-grained structure.In the aforementioned work the element deletion method is employed to investigate the fracture behavior of nanostructured metals and the properties of the interfaces are not considered.Here,the cohesive finite element method is used and the task is to uncover the effects of cohesive strength and the microstructural attributes on the tensile fracture behavior of the bimodal nanostructured Cu.The simulations show that when the cohesive strength of two phases reaches a certain level,the true stress-strain curves of any microstructure saturate.Furthermore,it is found that their overall mechanical responses depend heavily on the distribution and shape of the coarse-grained inclusions.It is believed that these results could provide useful insights into the development of advanced nanostructured materials for ballistic protection.