Dynamic plastic deformation and failure mechanisms of individual microcapsule and its polymeric composites

Functional materials are widely used by introducing functional microcapsules in the matrix. The individual microcapsule can be regarded as core-shell structure in micro-level. In this study, mechanical performance of individual microcapsule with different shell types (PUF, silica, and nickel) and corresponding microcapsule-modified polymers under quasi-static as well as dynamic compressions are studied experimentally and numerically. Results show that the strength of the nickel shell-based microcapsule is two orders higher than that of the other two microcapsules at different strain rates. More cracks and fragments are observed in microcapsule subject to dynamic loading, which indicates higher energy dissipation under impact. The inclusion of nickel shell-based microcapsule does not cause strength reduction of the resulting microcapsule-modified polymer at all strain rates, while the use of PUF and silica shell-based microcapsules lead to significant reduction of the composites strengths. Nickel shell-based microcapsule-modified polymer shows high strain rate sensitivity than the other two microcapsule-modified polymers. Furthermore, nickel shell-based microcapsule-modified polymer shows distinct failure modes when compared to the PUF and the silica shell-based microcapsule-modified polymers. While matrix cracks tend to penetrate through the weak PUF and silica shell-based microcapsules, they often propagate along the nickel shell-based microcapsule/epoxy matrix interface due to a much higher strength of the nickel shell-based microcapsule. After debonding, sliding of the fracture surfaces may lead to the final fracture of some weaker Ni microcapsules in the nickel shell-based microcapsule-modified polymer.