Modeling And Simulation Of Wood Mechanical Properties Based On Finite Element Theory

Wood is an important engineering material for people's life and economic construction.With the development of science and technology in industry field, it has been widely used as asuperior nature material. The material has been used for several thousand years, but itsmechanical properties, such as the difference of mechanical properties among species, crackpropagation, the deformation caused by changes in moisture content and the complex nonlinearmechanical performance with overload etc. is not yet fully understood by people. Timber'sstructure determines its mechanical properties, which estimate the value of timber andinfluence the processing and use of timber. Therefore, the detailed investigations and a betterunderstanding of timber's mechanical properties are very important.In this paper, the mechanical properties of macro and microstructure were studiedsystematically with a great deal of tests based on the former researches in the field. Thedistribution relation of the width of early wood, transition wood and latewood versus thenumbers of growth ring was achieved by observing the microstructure. The density versus thenumber of growth ring was determined by measuring the density of growth ring one by one.Slip specimens measured the stiffness of early wood and latewood versus the number ofgrowth ring. Due to the mechanical properties closed related with moisture content, shrinkagecoefficients of three main directions of wood versus growth ring was detected by tests. Duringthe modeling of wood mechanical properties, FEM and heterogeneous theory were applied formodel of growth rings assumed as the continuum. The average performance of wood fiber withthe other organizations was considered synthetically whose geometric and material informationwere integrated into an equivalent body. The average property of complex periodic-microstructure- material was substituted by the equivalent uniform continuum. The relativeequations between micro vector fields and macro ones were established through the boundaryconditions of stress and displacement in the basic units where the field of strain and stress wasobtained by known macro vector fields, geometric and physical equations. Finally, constitutiveequation that is the relation between macro stress and strain of special units was achievedaccording to heterogeneous theory with SOLID46adopted as a model to calculate the efficientperformance in the simulation software of ANSYS. The composite material theory used for themodeling research to the wood composite laminated structure and the strain and stress relationof single layer material under plane stress w as studied. The stiffness conversion wasconstructed by monolayer material versus macro axis. The macro structure of wood wasregarded as composite laminated structure integrated by growth rings. The strength wasanalyzed by composite material theory and malfunction was evaluated by HILL-CAI criterion. The result of tests was consistent with theoretical calculation. Crack plastic zone of wood withanisotropy was studied by HILL-CAI criterion, crack tip stress fields and yield criteria were setup, the effect that constant of anisotropy material influence on the performance of plastic zoneand the different stiffness ratios of early wood and latewood in growth ring impact of theplastic zone were analyzed. Meanwhile, the research result on plastic zone was verifiedthrough the microphotograph of wood microstructure and ANSYS simulation software. Thestrength, deformation and failure of wood are related with parameters on its structure, crackpropagation and fracture. The size of crack with stochastic being taken into account, curve ofwood strength factors was calculated by stochastic FEM, which had been verified by relatedexperiments. The results show that the fracture properties of wood were calculated andpredicted by stochastic FEM is feasible and applicable.In this study, finite element theory, homogenization theory, composite material theory andwood micro-mechanics are researched which are of cross-frontier research to improve theawareness on the mechanical properties of wood from micro to macro, expend the scope ofapplication, enhance the wood utilization level. The investigation is of great significance forsustainable development of wood industry.