Plastic waves in one-dimensional heterogeneous granular chains under impact loading: Single intruders and dimer chains

Elastic granular dimer chains (defined as arrays of repeating dissimilar material granule pairs) have shown promise for wave mitigation applications since it has been observed that for certain dimer mass ratios significant force attenuation can occur along the chain during dynamic wave propagation (Jayaprakash et al., 2013). However in many applications, applied forces are likely to be such that the elastic assumption would be violated at locations of high stress concentration - the granule contact points. In this work we seek to investigate the force transmitted through dimer chains and chains with a single intruder (i.e., differing granule from the surroundings), subjected to dynamic loading in the plastic regime. A split Hopkinson pressure bar was used to dynamically load one-dimensional metallic dimer chains and homogeneous chains of metallic spheres with single intruders. Loading magnitudes ranging from 10 kN to 35 kN were applied to these chains, producing significant plasticity in the beads. The results in each case were quantified by the ratio of the output to incident force from the granular chain. Transmitted force results were compared to those in elastic dimer chains for which force attenuation was controlled by the mass ratio of the dimer pair. In the plastic case, however, the propagating pulse was found to have a strong dependence on the yielding material, not on the dimer mass ratio. Although output force was significantly reduced over input force, the reduction was driven by plastic dissipation and not elastic attenuation mechanisms. Chains with a single intruder were also seen to behave differently when the intruder was relatively softer or harder than the remainder of the chain. For a softer intruder the transmitted force decreased as the intruder location moved further down the chain, while for a harder intruder the output force did not depend on intruder location and was roughly the same as that of a homogeneous chain, i.e., the harder intruder did not affect wave transmission.