Effects of high-intensity microwave (HIMW) treatment on mechanical properties and bending failure mechanisms of radiata pine (Pinus radiata D. Don)

This study investigated the effects of high-intensity microwave (HIMW) treatment on the mechanical properties of radiata pine wood. The treatment, conducted on sapwood and heartwood with 60% initial moisture content, involved varied microwave energy densities: 60, 80, and 100 kWh/m³. Tests evaluated tensile and compressive properties in three directions, alongside shear strength and bending properties. Acoustic emission (AE) and digital image correlation (DIC) techniques probed damage evolution under bending loads before and after HIMW treatment. As microwave energy density increased, compressive, tensile, and shear strength decreased, with heartwood being the most susceptible. Substantial reductions occurred in longitudinal compressive properties and tensile properties perpendicular to the grain. After HIMW treatment (80 kWh/m³ and 100 kWh/m³ for sapwood and heartwood, respectively), although there was a slight decrease in the modulus of elasticity and bending strength, there was a significant increase in bending plasticity. HIMW-treated specimens exhibited more high-frequency AE signals during elastic–plastic deformation, indicating more frequent fractures in the treated wood during three-point bending. Changes in the microscopic structure of the wood specimens caused by HIMW treatment increased the damage growth rate and stress redistribution efficiency during loading, augmenting the bending plasticity of wood.