Experimental Study On The Mechanical Properties Of Wood And The Numerical Modeling Strategies Of Wood

Wood is one of the oldest biomaterial which have found extensive structural applications owning to its low self-weight,high strength-to-density ratio and easy processing.In recent years,the extensive usage of new engineered wood products and the need to evaluate and strengthen the damaged wood components in ancient wooden structures stimulate a better understanding to the mechanical properties of wood.Establishing elaborate modeling strategies that enable elasto-plastic analysis of wood numerically is a crucial part of this job.In this dissertation,the experimental study was carried out to study the mechanical properties of wood,two modeling precedures were then proposed to tackle different problems.The proposed modeling strategies were validated and its potential applications were indicated.Firstly,Korean pine was adopted in this investigation as the experimental material to study the mechanical properties of wood,including the Young's moduli,shear moduli,Poisson's ratios,the coefficients of mutual influence,tension strengths,crushing strengths and shear strengths in various directions.The measured results were compared with the formula calculated by tensor transformation,the empirical Hankinson's formula and the yielding criterion for orthotropic materials.The mechanical behavior of Korean pine were then described quantitatively and qualitatively.Next,a morphology-based lattice model was established based on the microstructure and macro mechanical behavior of wood.The model was constituted by different spring elements connected to each other and the analytical solution to determine the stiffness and ultimate strengths of springs were given based on the principal of energy equivalence.The predicted results showed good agreement with the test results.In the next chapter,two constitutive models for wood were introduced.The first constitutive model was based on the Sun&Chen's single-parameter model for fiber composites and was modified to make it more suitable to reflect the nonlinear characteristics of wood under compressive load in arbitrary orientations.The second constitutive law was established in the frame of classic elasto-plasticity theory and aimed to simulate the behavior of wood under complex stress states.The model was compiled as the user subroutine and embedded into the ABAQUS software.At last,based on the research to the mechanical properties of wood and the FEA of a mortise-tenon joints,the analytical solution of a wooden beam under uniform load in traditional Chinese timber structures was given.The derived stress distribution in the beam provided an insight into the service state of the beam and its possible future failure modes.