Capsule based self-healing composites: New insights on mechanical behaviour based on finite element analysis

We have investigated the reinforcement mechanics of capsule-based self-healing composites (CSC) comprising poly(urea–formaldehyde) (PUF) capsules embedded in epoxy matrix using a micro-scale representative volume element (RVE) model. Finite element analysis was used to model four stages of loading, corresponding to elastic loading and fracture of pristine CSC (containing epoxy-filled capsules) and, following healing, of repaired CSCs (containing capsules depleted of healants), respectively. Predictions of the elastic modulus (E) during elastic loading and the local damage pattern within the CSC during fracture were obtained. The E was most sensitive to capsule volume fraction (V_p) but least sensitive to capsule distribution pattern. The E also depended on the state of the capsule. The E increased with increasing V_p in epoxy-filled capsule composite, suggesting that epoxy-filled capsules could provide reinforcement to the epoxy-based composite. However, E decreased with increasing V_p in empty capsule composites, indicating that empty capsules could not be depended upon for reinforcing the composite. When fracture began, capsules at close proximity, especially in agglomerates, could interact to promote further damage regardless of whether they were filled or empty; the damage pattern observed could be a prelude to mode 1 type fracture. These predictions led to wider implications concerning how agglomerates in the CSC could influence the mechanics of elastic loading and fracture of the composite.