Cellular materials have applications for impact and blast protection. Under impact/impulsive loading the response of the cellular solid can be controlled by compaction (or shock, see [3,4]) waves. Different analytical and computational solutions have been produced to model this behaviour but these solutions provide conflicting predictions for the response of the material in certain loading scenarios.The different analytical approaches are discussed using two simple examples for clarity. The differences between apparently similar "models" are clarified. In particular, it is argued that mass-spring models are not capable of modelling the discontinuities that exist in a compaction wave in a cellular material.

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Impact responses and damage induced by a drop-weight on GLARE 5 (3/2) fiber-metal laminates (FMLs) with various lay-up configurations were studied experimentally. The effect of specimen geometry was also considered. The damage characteristics were evaluated using both nondestructive ultrasonic and mechanicalsectioning techniques. Only the contour of the entire damage area could be obtained using ultrasonic C-scan, whereas more details of the damage were provided through the mechanical-sectioning technique. The impact properties of FMLs were affected by laminate stacking sequence. The first severe failure induced by low-velocity impact occurred as debonding between aluminum and the adjacent fiber-epoxy layer at the nonimpact side. It was followed by a visible crack in the outer aluminum layer at the nonimpact face. GLARE 5 made of unidirectional fibers had the least impact resistance; followed by cross-ply and angle-ply configurations; while the quasiisotropic lay-up showed the best in resistance to impact. By introducing circular, rather than square, geometry as the outer perimeter of the specimens, the damage patterns as well as impact behaviors changed due to the relative anisotropy of the specimen with respect to the specimen clamping.

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