木材本构模型研究进展

Research progress on constitutive model for wood

木材本构模型是木结构受力分析的基础。基于木材各纹理方向的单调加载、重复加卸载试验结果,总结了木材的失效机理及其非线性受力特征。在此基础上,梳理了木材经验本构模型、弹性本构模型、弹塑性本构模型和损伤本构模型的研究现状,分析了上述本构模型对木材非线性受力行为的表征能力及其存在的问题。结果表明:木材非线性受力特征包括顺纹及横纹受拉脆断、顺纹受压应变软化、横纹受压应变强化、顺纹和横纹剪切脆断、顺纹和横纹受压卸载时存在的不可恢复变形和刚度退化行为等;不同本构模型对木材非线性受力特征的表征能力不同,但弹塑性损伤本构模型最能全面反映其非线性受力机制。对于木材本构模型,亟待深入开展的研究工作,主要包括:建立基于木材宏观构造特征与物理性能的全部弹性常数预测模型;建立复杂受力状态下木材损伤机制与强度准则;建立可以考虑塑性与损伤耦合效应、材质劣化效应的弹塑性损伤本构模型,为进一步完善木材本构模型提供参考。

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.