Towards stitching reinforcement of veneer-based wood products: Influence of needle type, diameter, and substrate characteristics on penetration resistance and damage formation

Through-thickness reinforcement methods are widely used to enhance the mechanical performance of fibre-reinforced plastics (FRPs), yet their adaptation to wood veneers remains unexamined. This study presents a novel investigation into the feasibility and transferability of thread-based through-thickness reinforcement techniques, such as sewing or tufting, to wood veneers and engineered wood products, providing new insights into potential reinforcement methods and manufacturing approaches. Needle penetration resistance of wood veneers from different species (poplar, birch and beech), under varying moisture conditions, and with a selection of needle geometries were examined. The damage introduced through needle penetration was characterised in a biaxial load case (slow rate penetration testing according to ASTM F1306), and the extent of the damage was assessed with reflected-light microscopy. The overarching goal is to provide the basis for the development of an innovative sewing or tufting based reinforcement method for veneer-based wood laminates, which could function as a sustainable alternative to through-thickness reinforced FRPs. Results indicate that wood veneers can be penetrated by sewing needles at forces comparable to, though higher than, those found in FRP tufting processes. Additionally, needle geometry and moisture conditions of the veneers significantly influence the penetration process, affecting the required penetration forces substantially. While veneer perforation can lead to substantial degradation, the findings highlight key parameters for process optimisation, offering a pathway towards integrating through-thickness reinforcements in wood-based composites.