Analysis And Testing Of Stresses At Crack Tip Of Wood

In order to investigate the possibility of digital speckle correlation method in wood fracture mechanics, the digital speckle correlation method and finite element Ansys method are respectively applied in this study.In the research, some assumptions are given out, they are: (1) Orthotropic properties of wood; (2) Linear elasticity of wood; (3) Homology of wood. Furthermore twelve elastic contants of Beula platyphylla Suk. Specimens were measured in the condition of tempeture 10C and relative humidity 60%. The thesis is mainly around the establishment of digital speckle correlation measurement system and the calculation of finite element method, and opens research work from the theory and the experiment. The author herself looked up and analyzed home and abroad datum and materials in the realm of digital speckle correlation method, absorbing a brilliant achievement in finite element method, digital image processing, numerical analysis in recent years, and put forward to displacement types on the basis of assumption of the object's real deformation, then provided two new displacements types to be fit on complicated deformation, namely the isoparametric element with 4 nodes and the isoparametric element with 8 nodes to make digital speckle correlation method get away from the weakness that the traditional Taylor formula can not describe the subset with the complicated deformation completely, and finally develop a set of effectively test software of digital speckle correlation method to apply to the wood deformation. In the same time, the two new models are tested and verified by 3 kinds of normal displacement types in the precision. In addition, the paper still finished the calculations of 2d- and 3d -birch's models with fracture, using the finite element software Ansys, and compared the results of digital speckle correlation method with the results of finite element method, from the theories and the experiment validate digital speckle correlation method in the wood fracture mechanics,to provide a new experimental method for the wood fracture mechanics. Its main research results are as follows:1. With the finite element software of Ansys, the article studies the displacement field, strain field, stress field near the crack tip of the timber in 2d- and 3d-isothotropic models. To reflect the factual mechanic situation near the crack tip really, the 2d -and 3d -models adopt respectively two methods of element refinement and singular element to simulate the singular field near the crack tip, and finally get the precisely results that approximate the true value;2. Through the analysis of displacement types in digital speckle correlation, the article firstly introduced the isoparametric displacement types of the finite element method into digital speckle correlation calculation, and put forward to two displacement types to apply to the timber combining object's specific deformation, namely the isoparametric element displacement type with 4 nodes and the isoparametric element displacement type with 8 nodes;3. The article systematically discussed and studied digital simulation method. According to the brief deformation, the complicated deformation pattern is established firstly, which is used to the finite element calculation and digital speckle correlation calculation of three- pointed fiexural deformation, to get displacement field, strain field, stress field. On the contrast between the results of the finite element method and the results of digital speckle correlation method, the precision and authencity of digital speckle correlation method in the complicated deformation is validated;4. Through the comparasion of the results of the finite element method and the results of digital speckle correlation method, we can get the conclusion that the precision of finite element method is in accordance with digital speckle correlation method;5. Digital speckle correlation method is a new experimental mechanical method with the extensive and applied outlook. By means of the article's resea...