ENERGY ABSORPTION MECHANISMS IN CERTAIN FOAM MATERIALS

摘要

Understanding penetration mechanisms are critical in the design of armors and selection/development of armor materials. Along those same lines, understanding energy absorption mechanisms is also important in designing energy absorption structures for a number of applications such as advanced armors, naval ships, protective barriers for civilian structures against terrorists attack, including crash barriers for auto race tracks. Natural cellular and manmade materials and foams have better energy absorption capability through large deformation mechanism. However none of these materials can take heat the generated in common explosion, projectiles like RPGs impacts, or the missiles impacts. The material used in such applications should be able to resist shock as well as heat. The proposed paper examines the energy absorption mechanics of natural materials like balsa wood, manmade foams like PVC foams, and a recently developed Eco-Core foam material [1] and compare with each other. The Eco-Core is foam type material that is made up of 95% fly ash (by volume), high char yield binder, and other additives. Microscopic structure of fly ash shows hollow ceramic balloons of 20 to 300 mm diameter with a wall thickness of about 20 mm. The balloons are syntactically bonded together by a phenolic resin. Compressive response of most foams start with a linear stress-strain response, then a highly nonlinear response, finally end with stiffening due to densification [2]. A typical response is shown in Figure 1. These response depends on the type cell (open or closed), material, and the fracture characteristics. In the case of Eco-Core, it also depends on the binder properties and failure of micro bubbles. The material energy absorption capability also depends on the state-of-stress (confined or unconfined). This paper details compressive response of various foam materials under different amounts of confinement, through microscopic studies the failure mechanisms are identified and modeled. Failure mechanics of eco-core are used in further enhancing the energy absorption of the material.