Meso-structural optimization of patch-based composites for high-value prepreg offcuts reformatting

Up to 50% of the prepreg acquired by composite part manufacturers is discarded as offcuts due to nesting limitations. Treating those offcuts as waste represents a significant economic loss and a critical sustainability challenge. Since the material remains uncured, however, these offcuts can be reformatted into Patch-Based Materials (PBMs). Engineered meso-structures that control patch position and orientation, such as the Brick-and-Mortar (BaM) architecture, deliver the highest mechanical property retention. This study examines the tensile behavior of engineered PBMs derived from four distinct prepreg systems, evaluating property retention relative to the neat parent materials. Firstly, a theoretical analysis is provided for the influence of key design variables: patch length, parent material properties, i.e. cured ply thickness and interlaminar fracture toughness, and patch spatial arrangement. Experimental results demonstrate that increasing patch length from 5 to 50 mm increases asymptotically both stiffness and strength. Furthermore, utilizing prepregs with reduced thickness and enhanced toughness shifts the primary failure mode from delamination to fiber fracture, achieving the 50% theoretical strength limit in standard BaM architectures. Notably, when fiber-dominated failure is achieved, implementing a modified staggering pattern, called BaM 1/3, further elevates strength retention up to 66%. By elucidating the influence of these critical design parameters, this work provides a framework for maximizing the value of prepreg offcuts and to facilitate the transition toward a circular economy in composite manufacturing.