Strain analysis and plastic bending behaviour of laminated veneer lumber under high-frequency heating

High-frequency (HF) bending of laminated veneer lumber (LVL) has emerged as a prominent method for fabricating curved wooden components. By enabling rapid and uniform heating within an HF electric field, this process facilitates the efficient production of complex curvatures, enhances wood utilisation, and offers significant benefits, including high heating speed and superior product quality. This study investigates the large-strain deformation behaviour and multiscale mechanisms of LVL during HF bending using digital image correlation, micro-computed tomography, dynamic mechanical analyzer, and chemical analyses. Key results demonstrate that HF-induced moisture migration reduces the glass transition temperature, increases polymer chain mobility, and promotes plastic deformation. Strain field analyses reveal tensile stresses on the convex surface and compressive stress on the concave side, with interlayer shear playing a critical role in stress distribution. At the microscale, HF treatment reduces cellulose crystallinity, promotes hemicellulose degradation, and enhances the fluidity and dimensional stability of lignin. Thinner veneers exhibit improved adhesive penetration, leading to superior bonding and mechanical performance. This work provides theoretical foundations for optimising wood bending processes and advancing the application of curved LVL in sustainable furniture and smart manufacturing. • High-frequency heating enables laminated veneer lumber bending via unique thermo-hydro-mechanical coupling. • Multiscale analysis reveals high-frequency heating softening and deformation mechanisms. • Revealed the distribution law of gradient strain distribution and neutral axis shift during LVL bending. • Elucidated the influence mechanism of veneer thickness on adhesive penetration and component mechanical properties.