Effect of high strain rate on the mechanical properties of spruce, birch, alder and larch under different moisture conditions and its implications for disintegration process

Spruce wood, along with birch, alder, and larch, represents a key raw material for the production of wood-based composite materials. To fully utilize offcuts and residual biomass generated during logging or the primary processing of native wood and subsequent preparation of the input semi-finished product, a process of secondary disintegration is employed using ring-type flakers operating under high strain rates. Optimal arrangement and orientation of the input wood feed relative to the motion of the flaking knives is essential for predicting the size and quality of the resulting flakes. To support this optimization, the mechanical properties of selected wood species were analysed in the longitudinal, transverse, and diagonal directions. Tests were carried out at two moisture conditions—after felling and after drying—and included both quasi-static and dynamic mechanical experiments. It was shown that strain rate has a fundamental influence on the slope of the optimized energy absorption–stress curve and on the overall mechanical behaviour of wood across different directions of its orthotropic structure. Furthermore, wood moisture content was found to play a decisive role in determining the resulting chip morphology and failure mode of the material.