Designed intermittency in interlaminar fracture via kirigami-induced crack-front widening

Laminated composite materials remain vulnerable to Mode I delamination. Here, we demonstrate that kirigami-inspired through-thickness cuts can deliberately introduce and control crack-propagation intermittency in carbon-fibre/epoxy laminates by architecting the crack front. Tests on rectangular and trapezoidal patterns, supported by simulations, X-ray CT, and a crack front width model, reveal four distinct stages: baseline propagation; cut entry, marked by a load drop due to a reduced effective width; cut-controlled intermittent propagation, where coupled deformation widens the crack front, increasing its effective length and stored elastic energy; and post-cut propagation, which returns to the baseline trend. Trapezoidal cuts maximise crack-front widening and increase both the load and the apparent energy-release rate required for crack re-initiation by up to fourfold in the tested specimens compared with unpatterned laminates. Rather than relying on interfacial modification or material alteration, this study establishes a proof-of-concept geometry-assisted strategy for tailoring Mode I delamination behaviour in existing laminated composites. By converting delamination into designed, repeatable intermittency, this geometry-driven and material-agnostic approach opens a new design space for enhancing interlaminar resistance. However, broader structural applications require further validation to quantify stress concentrations, adherend failure risks, and associated in-plane performance trade-offs.