Abstract
The anisotropic material behavior of wood, considered as a cylindrically orthotropic material with annual rings, leads to several different failure mechanisms already under uniaxial stresses. Stress interaction becomes important in the engineering design of structural elements and is often predicted by failure criteria based on uniaxial properties. The prediction quality of failure criteria has been assessed with longitudinal shear stress interaction, though less is known on rolling shear stress in interaction with stress perpendicular to the grain. The study aims at investigating the corresponding mechanical behavior of Norway spruce (Picea abies) clear wood by validating failure envelopes for stress combinations in the cross-sectional plane, based on experimental investigations. For this purpose, a test setup that controls the stress interaction and loading of clear wood along pre-defined displacement paths needed to be developed. Experimentally defined failure states could then be compared to failure surfaces predicted by the phenomenological failure criteria. Material behavior was quantified in terms of stiffness, strength, and elastic and post-elastic responses on dog-bone shaped specimens loaded along 12 different displacement paths. A comparison with failure criteria for two nominal compressive strain levels showed that a combination of failure criteria would be required to represent the material behavior and consider the positive effect of compressive stresses on the rolling shear strength. The findings of this work will contribute to studying local stress distribution of structural elements and construction details, where stress interactions with rolling shear develop.
Highlights
Multiaxial and complex stress states can arise in timber structures depending on the position and direction of the applied force with regards to the wood grain direction
The annual ring structure in a radial (R)-tangential (T) cross-section of wood that is loaded by uniform compression perpendicular to the grain leads to a non-uniform stress state and combination of normal stresses in the R and T direction with rolling shear
The aim of this paper is to investigate the mechanical behavior of clear wood under stresses perpendicular to the grain in interaction with rolling shear stresses
Summary
Multiaxial and complex stress states can arise in timber structures depending on the position and direction of the applied force with regards to the wood grain direction This requires special attention due to the material’s anisotropy as a consequence of its heterogeneous and porous microstructure (Kollmann et al 2012). Threedimensional anisotropic phenomenological failure criteria have been proposed for this purpose These merely describe the phenomenon of failure, but neither the material behavior nor the failure mechanism (Cabrero et al 2012; Kasal and Leichti 2005). Most of these phenomenological failure criteria were developed for composite materials based on isotropic failure criteria The validation of these anisotropic failure criteria for stress interaction in natural orthotropic materials such as wood has attracted less attention, especially for the combinations with rolling shear stresses
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