Mechanical characteristics of wood-bark interface of shrub willow

Abstract

The mechanical behavior of the wood-bark interface of shrub willow was tested to investigate the influence of key factors: harvest season, moisture content, and cultivars. The mechanical properties enable the design and optimization of the performance of debarking equipment for short-rotation woody stems and can help improve understanding of the mechanical performance of the wood-bark interface. Results show that the low moisture content samples have a significantly higher shear modulus, G (Mean =0.34 GPa) and modulus of toughness Ut (Mean = 12.84 kPa). However, the degree of ductility (0.02) and the ratio of ultimate strain εu to strain ε50 (2.18) are lower for low moisture content samples. Different willow cultivars have no significant influence on the mechanical properties of the wood-bark interface tested. Results also reveal that the values of ultimate strain εu (0.11), modulus of toughness Ut (16.09 kPa), and degree of ductility (0.031) are significantly higher for samples collected in the dormant season compared to the growing season. Covariance analysis reveals that aspect ratio of the sample has a significant effect on shear modulus, G (p = 0.041), ultimate strain, εu (p = 0.008), modulus of toughness (p = 0.012) and degree of ductility (p = 0.001). Identifying the combination of these desirable properties provides a framework to achieve the maximum debarking efficiency and effectiveness for short-rotation woody crops.