Characterizing fracture toughness of C/C-ZrC-SiC composites: experiment, element-based peridynamics simulation and inversion

Fracture toughness is a key parameter for assessing structural integrity. Due to their quasi-brittle nature, large fracture process zones, and pronounced fiber bridging effects during crack propagation, C/C-ZrC-SiC composites exhibit distinct initiation and steady-state fracture toughness values. To characterize the steady-state fracture toughness, larger compact tension (CT) specimens were tested using the modified compliance method (MCM) with defining equivalent crack length. A trilinear bridging law was proposed to model the relationship between the energy release rate and crack opening displacement. Based on this law, an R-curve evolution equation was derived and integrated into element-based peridynamics (EBPD) simulations. Within the EBPD framework, the critical strain energy release rate was dynamically updated as a function of crack extension. The load–displacement curves and R-curves predicted by the EBPD model showed good agreement with experimental data. Furthermore, the R-curve evolution parameters can be inversely identified using Bayesian optimization. This approach leverages EBPD simulation results combined with experimental data from standard CT specimens. This inverse method determining the R-curve not only reduces testing costs but also demonstrates strong generality. The proposed inverse fracture toughness characterization framework offers significant potential for quantitatively evaluating the fracture performance of other quasi-brittle materials.