Dynamic crushing of cellular materials: A unique dynamic stress-strain state curve

Cellular materials under high loading rates have typical features of deformation localization and stress enhancement, which have been well characterized by one-dimensional shock wave models. However, under moderate loading rates, the local stress-strain curves and dynamic response of cellular materials are still unclear. In this paper, the dynamic stress-strain response of cellular materials is investigated by using the wave propagation technique, of which the main advantage is that no pre-assumed constitutive relationship is required. Based on virtual Taylor tests, a series of local dynamic stress-strain history curves under different loading rates are obtained by Lagrangian analysis method. The plastic stage of local stress-strain history curve under a moderate loading rate presents a crooked evolution process, which demonstrates the dynamic behavior of cellular materials under moderate loading rates cannot be characterized by a shock model. A unique dynamic stress-strain state curve of the cellular material is summarized by extracting the critical stress-strain points just before the unloading stage on the local dynamic stress-strain history curves. The result shows that the dynamic stress-strain states of cellular materials are independent of the initial loading velocity but deformation-mode dependent. The dynamic stress-strain states present an obvious nonlinear plastic hardening effect and they are quite different from those under quasi static compression. Finally, the loading-rate and strain-rate effects of cellular materials are investigated. It is concluded that the initial crushing stress is mainly controlled by the strain-rate effect, but the dynamic densification behavior is velocity-dependent. (C) 2016 Elsevier Ltd. All rights reserved.