Interlaminar toughening mechanisms: In situ growth and modelling

Micromechanistic simulation of constrained interlaminar fracture occurring during delamination of toughened materials has received limited attention within the polymer composites community. With recent advances in computational resources and the development of arbitrary cracking models, such as the Augmented Finite Element Method (A-FEM), more complex microstructures can now be tackled featuring multiple interacting cracks. It has been established that Mode I crack propagation in particle-toughened interlayers within a CFRP laminate involve a process zone rather than a distinct crack tip. This involves multiple cracks forming ahead of the main crack that then coalesce, leaving behind bridging ligaments that may then provide traction across the crack flanks. Preliminary idealised 2D AFEM models are presented in this work, that highlight the relative role of neat resin to ply interface cohesion, and the incidence of 'idealised de-bonds'/discontinuities, in maintaining the crack path within the interlayer. Four-dimensional time-resolved computed tomography (CT) experiments complement the idealised models, with the chronology of damage events and resultant crack paths being directly identified in different toughened microstructures.