Impact response of low-density foam impinging onto viscoelastic bar: A theoretical analysis

The Taylor-Hopkinson test is widely used in predicting the dynamic strength of materials. For low-density foam materials, the output bar in the Taylor-Hopkinson test is often made from much weaker materials like polymethylmethacrylate (PMMA) to reduce the wave impedance mismatch between the foam sample and the output bar. These low impedance materials exhibit viscoelastic properties and may affect the dynamic stress prediction of foam samples. In this paper, the shock wave theory for the foam sample in conjunction with the viscoelastic wave propagation in the output bar is employed to illustrate the influence of the viscoelastic output bar on the dynamic response of foam samples in the Taylor-Hopkinson impact. The theoretical model presented in this paper can be degenerated into previous elastic target bar model and rigid target bar model. Finite element simulations are further performed to verify the proposed theory. The influence of material parameters on the final deformation of the foam sample, impact duration and residual velocity of the foam sample are investigated. The results in this paper not only help in understanding the effect of the viscoelastic bar on the dynamic response of foam samples, but also set up guidelines to perform the Taylor-Hopkinson test more precisely.