A Fast Linear Method for Delamination Onset Prediction under Mixed Modes in Composite Structures

The knowledge of the delamination onset load is crucial in the preliminary design of composite laminates, particularly when mixed-mode fracture processes, governed by the interaction between Mode I and Mode II energy release rates (GI–GII), control the damage initiation. Conventional high-fidelity approaches, such as nonlinear progressive damage analyses, cohesive zone modelling, or VCCT-based simulations, provide detailed predictions of delamination onset but are computationally expensive and therefore impractical for early-stage design iterations involving large design spaces. This work introduces a computationally efficient reduced-order methodology for estimating the delamination initiation load using only linear static analyses and linear eigenvalue buckling analyses. The proposed method employs mixed-mode fracture criteria to correlate eigenvalue-derived critical load with the critical GI/ GII combination at the delamination front. A systematic numerical campaign is performed on a single composite structure by varying the radius and through-thickness position of an embedded circular delamination, enabling a direct comparison between the proposed linear approach and nonlinear VCCT-based reference solutions. By avoiding nonlinear material modelling and contact algorithms, the method achieves orders-of-magnitude reductions in computational cost while preserving accuracy within clearly defined applicability limits. These limits are quantified and expressed in terms of a novel dimensionless parameter, which allows an a priori discrimination between Mode I–dominated and mixed-mode delamination onset conditions. The resulting fast-assessment tool is particularly suited for conceptual and preliminary design, enabling rapid elimination of structurally inefficient stacking sequences, geometries, and boundary conditions.