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Sandwiched hollow sphere structure may have the potential to provide better ballistic impact protection as compared with monolithic plate based on the same weight and impact area. In the previous study of a sandwiched hollow sphere structure by the authors, a novel unit cell was created as a basic building unit of the structure, the tumbling effect was observed for significant impact energy absorption, and the existence of an optimal yield stress or hardness was proved for maximizing the impact energy absorption. However, the impact energy absorption ability of the sandwiched hollow sphere structure may also relate to many other factors. In this study, the diameter relation between the incoming projectile and the spheres in the sandwich core, the projectile initial impact velocity, and the sphere arrangement in the sandwich core are examined. It is revealed that the first layer sphere diameter should be comparable to the diameter of the incoming projectile, the diameter of spheres in different layers in one sandwich core should either decrease or increase monotonically, and there exists a critical impacting speed, at which the sandwiched sphere structure is most effective for impact energy absorption, etc. All these findings make the sandwiched hollow sphere structure a promising new member to the passive armor family. [ABSTRACT FROM PUBLISHER]

The interaction between a projectile and metal-matrix composites (MMCs) was investigated in terms of macro cracking, petalling and particularly grain deformation of a matrix alloy at the hole section caused by the projectile at high velocity impact. Metal matrix composites were manufactured by squeeze casting using Al alloys reinforced with Al2O3 or SiC. Additionally, laminated composites with SiC particles and back side supported by Kevlar 49® were manufactured and their ballistic behavior tested. The composite and unreinforced Al alloy targets were subjected to ballistic impact with an armor piercing projectile of 7.62mm caliber at a speed in the range of 770-800 m/s. The macro examination focused on cracking and petalling after impact. The investigation of grain deformations of matrix alloy was conducted by light microscopy in the hole section created by the projectile. The hole section created by the projectile had different profiles. Around the hole sections, different grain deformation rates in different directions took place for reinforced and unreinforced Al alloys. Strong friction took place between the projectile and hole surface and the velocity of the projectile was decreased suddenly in the hole as it met the reinforcement particles in the composite body. These led to deformations of the projectile surface and grain surrounding the reinforcement. In the case of laminate composites, the laminates were fractured and deformed in the direction of projectile movement [ABSTRACT FROM AUTHOR]