Ballistic performance study on the composite structures of multi-layered targets subjected to high velocity impact by copper EFP

Investigation ballistic performance of metallic target against projectile impact is of practical interests in the design of protective composite structures like armors. Subjected to high velocity impact of explosively formed projectile (EFP) which is a kind of easy-deformable and soft projectile, the ballistic performance of monolithic and composite structures including three-layered in-contact and spaced mild steel targets has been studied. Terminal effects of multi-layered targets are summarized to assess the pros and cons of composite structures from a macro perspective. Correspondingly, microstructure evolution of the crater and morphology features of fracture surfaces are analyzed to reveal failure mechanisms of sub-structures. The results show that the monolithic target presents less effective than in-contact or spacing multi-layered targets as the dominant response of multi-layered targets are local plastic deformation and bulging which involved bending and stretching behavior. The multi-layered targets with the thinner sub-structures in front and thicker sub-structures at back are superior to resist the penetration of the copper EFP. Moreover, the air gap increases the ballistic resistance of three-layered targets especially as the width of air gap is larger than one quarter length of projectile. The results will not only help to reveal different penetration mechanisms by which structures respond to dynamic extremes but also help to improve the ballistic resistance of armors.