Numerical analysis of fracture in core-shell particle reinforced composites

The fracture of core-shell particle reinforced composites was simulated using a crack phase field method. A pre-existing crack may grow along the interface between the core and shell (core debonding), may penetrate the shell and the core (trans-core fracture), or may grow in the matrix (brittle fracture in the matrix). Shell fracture behaviours resulting from the competition between the fracture resistance and fracture driving force are crucial to the crack growth mechanisms. It was found that moderate strength and low modulus of the shell favoured trans-core fracture, and low strength and high modulus of the shell favoured core debonding. The effects on the overall mechanical properties were also identified. The composite strength usually benefited from stiffer and tougher components, regardless of the crack growth mechanisms, while the composite toughness was more complex. The toughening effect was highly related to how the crack evolved, as core debonding improved the toughness at the significant cost of strength, and trans-core fracture contributed most to the toughness with a slight reduction in strength compared with the matrix. These findings indicate design strategies for epoxy composites which can achieve a balance of strength and toughness, enabling the design of safer lightweight composites for electric vehicles and transport applications.