Experimental characterization and numerical simulation of interfacial fracture toughness in composite materials

Traditional laminate tests are affected by structural effects and cannot accurately capture intrinsic fiber/resin interface fracture parameters. A mesoscale method was proposed to characterize interface fracture toughness. Bilayer fiber-bundle asymmetric double-cantilever-beam (BFADCB) and asymmetric single-leg-bending (BFASLB) specimens were designed to achieve mixed-mode loading from pure mode I to high mode II ratios. An analytical compliance model included shear effects and interface-stress continuity. The strain energy release rate was calculated using an equivalent-crack-length method. Experiments and finite element analysis determined mode mixity. The Benzeggagh-Kenane (B-K) criterion identified interface fracture parameters, and numerical results validated them. The pure mode I fracture toughness is 0.1275 N·mm⁻¹. BFADCB, BFSLB, and BFASLB specimens give total fracture energies of 0.2173, 0.4423, and 0.6359 N·mm⁻¹, with mode mixities of 0.1124, 0.4524, and 0.5801. The fitted mode II fracture toughness is 1.15 N·mm⁻¹, and η is 1.35. Numerical results agree with experimental load-displacement responses and fracture energies. The BFADCB error is -15.51%, while other errors are within 10%. The method describes mixed-mode fracture behavior and provides reliable parameters for multiscale damage analysis of composite materials.