Crack Extension and Possibility of Debonding in Encapsulation-Based Self-Healing Materials

The breakage of capsules upon crack propagation is crucial for achieving crack healing in encapsulation-based self-healing materials. A mesomechanical model was developed in this study to simulate the process of crack propagation in a matrix and the potential of debonding. The model used the extended finite element method (XFEM) combined with a cohesive zone model (CZM) in a two-dimensional (2D) configuration. The configuration consisted of an infinite matrix with an embedded crack and a capsule nearby, all subjected to a uniaxial remote tensile load. A parametric study was performed to investigate the effect of geometry, elastic parameters and fracture properties on the fracture response of the system. The results indicated that the effect of the capsule wall on the fracture behavior of the matrix is insignificant for t(c)/R(c) ≤ 0.05. The matrix strength influenced the ultimate crack length, while the Young’s modulus ratio E(c)/E(m) only affected the rate of crack propagation. The potential for capsule breakage or debonding was dependent on the comparative strength between capsule and interface (S(c)/S(int)), provided the crack could reach the capsule. The critical value of S(c,cr)/S(int,cr) was obtained using this model for materials design.