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 cellcore (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.

Automated summary

This study experimentally investigates the effect of defects on foam materials and proposes a statistical model that considers the influence of defects. The results show that the defect of missing cell-wall greatly affects the compressive behaviors of foams, while the defect of missing cell-core has a negligible influence on mechanical properties.