Effect of heat and steam bending on the longitudinal and radial mechanical properties and derived acoustical indices of spruce and maple wood

This study investigates the effects of steam and heat bending on the longitudinal and radial vibro-mechanical properties of spruce (Picea abies) and maple (Acer spp.). More than 100 thin beams were bent to nominal strain levels of approximately 0.7 % and compared to reference specimens using laser vibrometry and modal analysis combined with finite element model updating. X-ray microtomography (2 mu m voxel size) was performed on selected specimens to examine the cellular-scale integrity after bending. After re-conditioning at 50 % RH and 25 degrees C, density showed no statistically significant change. A modest reduction in longitudinal stiffness was observed, more pronounced in spruce, while the longitudinal loss factor increased significantly for both species, leading to decreased radiation ratio and acoustic conversion efficiency indices, particularly in spruce. These results provide quantitative trends relevant to manufacturing of bent wood, the mechanical and vibroacoustical design of bent wood parts and structures.