Research progress on constitutive model for wood

Abstract

The constitutive model of wood is the basis of the mechanical analysis of timber structures. Based on the experimental results of wood under monotonic and repeated loading / unloading in each grain direction, the post failure mechanisms and nonlinear characteristics of wood were summarized. On the basis of this summary, the research status of empirical constitutive, elastic constitutive, elasto-plastic constitutive and damage constitutive models of wood as well as their ability to characterize the nonlinear mechanical behavior of wood and the existing problems were analyzed. The results show that the nonlinear mechanical characteristics of wood include the brittle fracture under parallel- / perpendicular-to-grain tension, strain softening under parallel-to-grain compression, strain hardening under parallel-to-grain compression, brittle fracture under parallel- / perpendicular-to-grain shear, large unrecoverable deformation and degradation of unloading stiffness under parallel- / perpendicular-to-grain compression, etc. Different constitutive models are capable of characterizing different aspects of the nonlinear characteristics of wood, but the elasto-plastic damage constitutive model can best reflect its nonlinear mechanism. Finally, it is pointed out that the future research should be carried out systematically and deeply from the following aspects: prediction models for all the elastic constants based on macro structural characteristics and physical properties of wood; the damage mechanism and strength criteria of wood under complex stress conditions; and the elasto-plastic damage constitutive model considering the coupling effect of plastic and damage mechanism and the material deterioration effect. The research provides a good reference for improving the constitutive model of wood in the future.