Understanding the effect of defects on compressive behaviors of closed-cell foams: Experiment and statistical model

Although defects cannot be avoided in foam materials, they are barely considered in existing models where relative density plays a dominating role. Despite sharing the same relative density, foams with and without defects may exhibit different mechanical properties. To study the effect of defects, this paper experimentally investigates the closed-cell foams with different levels of defects, and proposes a statistical model considering the influence of defect. The polylactic-acid Voronoi foams with deliberately induced defects, including missing cell-core (30% and 50%) and missing cell-wall (0%–50%), are firstly produced using the additive manufacturing technique. After that, a number of quasi-static experiments are conducted. Results indicate that the defect of the missing cell-core insignificantly affects the mechanical properties, while, the defect of the missing cell-wall greatly affects the compressive behaviors of foams. In particular, specimens with the defect of a missing cell-core correspond to intact foams with a larger cell-size, and only cell-wall buckling is observed. For foams with the defect of a missing cell-wall, a new deformation mechanism named cell-wall vacancy occupation is defined and reported. This mechanism makes specimens exhibit a lower stress level and a more obvious strain hardening behavior. Based on the experimental data, a statistical model is established. This model offers both forward prediction and inverse calculation of the effect of defect on the compressive behaviors of foams with good accuracy.