Mode-II interlaminar damage in carbon/epoxy composites fabricated via hot-press and vacuum-bagging techniques

Understanding mode II delamination in thermoset composites remains incomplete, particularly when fabrication-induced variability affects interfacial characteristics and fracture performance. This research fabricates unidirectional carbon/epoxy prepregs via hot-press (HP) and vacuum-bagging (VB) techniques and evaluates their interlaminar fracture behaviour through End-Notched Flexure (ENF) testing. Results indicate that the mode II fracture toughness ( G IIC ) of VB specimens (1387 N/m) is approximately 33 % lower than that of HP specimens (2058 N/m). Scanning electron microscopy (SEM) reveals reduced shear cusp density and matrix cracking in VB specimens. Delamination behaviour is simulated using a symmetric Trapezoidal Traction-Separation Law (TTSL) with pseudo-plasticity parameter Γ = 0.99, which, aside from differing G IIC values, employs a consistent set of cohesive parameters (interface stiffness k IIC = 4.5 × 10 5 MPa/mm and interface strength t u,II = 100 MPa) to accurately reproduce the force-displacement response in both fabrication methods. A higher G IIC value corresponds to greater crack extension ( da ) in simulated damage profiles, with da = 2.9 mm and 2.5 mm in HP and VB specimens, respectively. The numerical model is further validated using VB specimens with varied initial crack lengths, consistently producing reliable results. These outcomes validate the proposed unified framework, with all cohesive parameters, except for the experimentally determined G IIC , which are kept constant ( Γ, k IIC and t u,II ). This approach significantly reduces the need for extensive parametric studies in numerical simulations, thereby improving efficiency and consistency. • Carbon/epoxy composites are fabricated via hot-press and vacuum-bagging methods. • Hot-press specimens exhibit higher mode II fracture toughness. • Shear cusps in hot-press samples are shorter and more densely packed. • A symmetric trapezoidal law models mode II delamination behaviour effectively. • Mode II fracture toughness solely governs the numerical simulation methodology.