Propagation of a stress wave through a virtual functionally graded foam

Abstract

Stress wave propagation through a Functionally Graded Foam Material (FGFM) is analysed in this paper using the Finite Element Method. A Finite Element model of the Split Hopkinson Pressure Bar (SHPB) is developed to apply realistic boundary conditions to a uniform density foam and is validated against laboratory SHPB tests. Wave propagation through virtual FGFMs with various gradient functions are then considered. The amplitude of the stress wave is found to be shaped by the gradient functions, i.e. the stress can be amplified or diminished following propagation through the FGFMs. The plastic dissipation energy in the specimens is also shaped by the gradient functions. This property of FGFMs provides significant potential for such materials to be used for cushioning structures.

Dynamic crushing of uniform and density graded cellular structures based on the circle arc model

“…Ali et al (2008) established a graded energy absorbing structure-a inspiration from the geometry in a banana peel, and gave the theoretical prediction of the behavior under low velocity based on the equations derived by Gibson and Ashby (1997). Kiernan et al (2009) had found the superiority of graded cellular materials on impact resistance and energy absorption for creating impact resistant structures and cushioning materials. Compared with a uniform foam with equal mass, Cui et al (2009) suggested that a functionally graded foam can exhibit superior energy absorption.…”

Towards a virtual functionally graded foam: Defining the large strain constitutive response of an isotropic closed cell polymeric cellular solid

“…This would build upon the work already carried out by Cui et al, [2] and Kiernan et al, [3]. While the methodology outlined in this paper appears to achieve global results quite similar to those of the HEX model while using only one independent input parameter, it is unlikely to be a successful method when studying the local deformation of a foam on a cellular scale.…”

“…Its dimensions are 0.5m 3 . The four nodes of the bottom face are constrained in the vertical direction while a velocity boundary condition of -0.425 m·s −1 is applied to nodes of the top face, giving a simulation time of 1 second.…”

Prediction of Internal Defect Area in Wooden Components by Stress Wave Velocity Analysis

“…The principle of stress wave testing is based on differences in the velocity of stress waves propagating in different materials, since the velocity of sound in healthy wood is much higher than in voids or in decaying wood (Halabe et al 1997;Wang et al 2004;Feng and Li 2008). Several studies of this technology have been performed, both experimentally and with simulations (Kiernan 2009). These studies have indicated that stress wave testing can effectively diagnose the defects in the wood (Liang 2008).…”