Effect of fibre–matrix interface fracture properties on fibre bridging mechanisms in mixed-mode delamination of unidirectional composite laminates: A numerical study

Fibre bridging can enhance the damage tolerance of composite laminates by shielding the crack tip during delamination, yet the influence of interface fracture properties on fibre bridging mechanisms remains insufficiently understood. This work employs an established multiscale mechanical framework to systematically investigate how fibre-matrix interfacial strength and toughness affect fibre bridging during mixed-mode delamination in DCB specimens. A parametric study varies these interface properties for glass and polypropylene fibre bundles as bridging ligaments. Absolute and normalised fracture resistance curves quantify the total toughening effect and relative extrinsic toughening contribution of fibre bridging. Increasing fibre-matrix interface fracture toughness raises the fracture resistance but reduces the extrinsic fibre bridging contribution. Conversely, excessively high fibre-matrix onset strengths shorten the bridging zone and promote premature bundle breakage. The toughening effect depends on the ligament material, with glass fibre bundles favouring higher fibre—matrix onset strengths than polypropylene bundles. Mode I shows the strongest sensitivity to fibre-matrix interface properties and develops the longest bridging zones, whereas the mode II-dominated response is governed more strongly by the intrinsic fibre-matrix interface fracture toughness. These findings provide mechanistic insight into how interface fracture properties govern fibre bridging and guide interface engineering according to ligament material and mode mixity.