Mechanical behavior and self-healing mechanism of polyurea-based double-walled microcapsule/epoxy composite films

• The epoxy composite films modified by polyurea-based double-walled microcapsules obtain a strong self-healing ability. • The microcapsules are well dispersed in the epoxy matrix. • The composite films exhibit good mechanical properties and their healing efficiency can reach up to 61 %. • Two types of self-healing fracture behaviors and its self-healing mechanism of the composite films are explained by analyzing the variation and StS of Y-direction strain field. The built-in self-healing capability, which can substantially repair the damaged polymeric materials, has become research hotspots in recent years. In this study, double-walled microcapsules were introduced in epoxy composite films to obtain a strong self-healing ability, and the embedded microcapsules were produced by the previous studies. The microstructure and micromechanical properties of the composite films were characterized by scanning electron microscope (SEM) and nanoindentation, and its mechanical behaviors and self-healing mechanism during the tensile process were tested by using the digital speckle correlation method (DSCM). The results showed that the epoxy composite films with 3.0 wt% microcapsules had the highest mechanical property improvement and the composite films with 5.0 wt% microcapsules achieved the highest self-healing efficiency of 61 %. In addition, two typical self-healing behaviors of the composite films were obtained by analyzing and interpreting the Y-direction strain field and St S value through DSCM, the mechanism of self-healing procedure was proposed.