Abstract
Cellular materials have potential application as absorbers of energy generated by high velocity impact. CTH, a Sandia National Laboratories Code which allows very severe strains to be simulated, has been used to perform very high resolution simulations showing the dynamic crushing of a series of two-dimensional, stainless steel metal structures with varying architectures. The structures are positioned to provide a cushion between a solid stainless steel flyer plate with velocities ranging from 300 to 900 m/s, and an initially stationary stainless steel target. Each of the alternative architectures under consideration was formed by an array of identical cells each of which had a constant volume and a constant density. The resolution of the simulations was maximised by choosing a configuration in which one-dimensional conditions persisted for the full period over which the specimen densified, a condition which is most readily met by impacting high density specimens at high velocity. It was found that the total plastic flow and, therefore, the irreversible energy dissipated in the fully densified energy absorbing cell, increase (a) as the structure becomes more rodlike and less platelike and (b) as the impact velocity increases. Sequential CTH images of the deformation processes show that the flow of the cell material may be broadly divided into macroscopic flow perpendicular to the compression direction and jetting-type processes (microkinetic flow) which tend to predominate in rod and rodlike configurations and also tend to play an increasing role at increased strain rates. A very simple analysis of a configuration in which a solid flyer impacts a solid target provides a baseline against which to compare and explain features seen in the simulations. The work provides a basis for the development of energy absorbing structures for application in the 200–1000 m/s impact regime.
Highlights
A common requirement in the design of many structures and vehicles is the ability to ameliorate the effects of projectile impact or collisions
Porous or cellular materials have demonstrated superior energy absorption under shock or impact loading when compared to monolithic materials [1,2], while offering the benefit of improved strength to weight ratios
We described a study in which lattices consisting of an array of intersecting stainless steel rods were manufactured using an additive manufacturing technique known as Selective Laser Melting (SLM) [29]
Summary
A common requirement in the design of many structures and vehicles is the ability to ameliorate the effects of projectile impact or collisions. A variety of cellular structures have been investigated with the aim of improving understanding of compressive response and maximising energy absorption over a range of representative impact conditions These include metal [3,4,5] and polymeric [6,7,8,9] foams, composites [10,11,12] and honeycombs [13,14,15]. One notable feature of this class of materials is the enhancement of crushing strength observed under dynamic loading due to inertial effects, as seen by Reid and Peng [16] in wood, Tan et al [17] in aluminium foams and Xue and Hutchinson [18] and Wu and Jiang [19] in metallic honeycombs. This phenomenon has been the subject of a numerical study by Liu et al [20], the conclusions of which identify a critical velocity above which inertial effects become significant
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