Experimental study on the mechanical properties of wood subjected to combined perpendicular-to-grain normal and rolling shear loads

Wood is frequently exposed to complex stresses within timber structures, underscoring the importance of understanding its mechanical properties under such scenarios. This study examines the mechanical behavior of wood under combined transverse compression/tension and rolling shear stresses using an MTS testing machine equipped with a custom-designed normal loading device. A total of 48 specimens were prepared and tested, and the failure modes and rolling shear stress-strain curves at varying normal stress levels were analyzed. The findings reveal that transverse tensile stress reduces rolling shear strength and peak strain while increasing the shear modulus, indicating a tensile stiffness effect. In contrast, compressive stress perpendicular to the grain enhances rolling shear strength and increases nonlinearity of the shear stress-strain curves. Furthermore, the applicability of several commonly used orthotropic strength criteria, including Hill, Norris, Hashin, Tsai-Wu, van der Put, and Hoffman, was systematically evaluated using test data from both this study and existing literature. The evaluation demonstrated that each strength criterion has unique strengths in describing the combined normal-shear failure behavior of wood, with no single criterion universally applicable across all stress states. Optimal stress ranges for each criterion were identified, with the van der Put and Hill criteria proving most suitable for characterizing specific aspects of wood strength failure under combined transverse normal and rolling shear stresses. •A novel combined normal-shear loading device was designed specifically for conducting biaxial experiments.•Combined transversal tension/compression and rolling shear performance were investigated, and the influence of normal stress on shear behavior was revealed.•The applicability of various commonly used orthotropic strength criteria in predicting the combined transverse normal and rolling shear strength behavior was systematically assessed.•The van der Put and Hill criteria were the most suitable for characterizing specific aspects of wood strength failure under combined transversal normal and rolling shear stresses.