Application Of Digital Speckle Correlation Method And Fractal Theory In Mechanical Analyses Of Wood

Materials elastic modulus is an important parameter characterized by the mechanical properties of the materials, elastic modulus and internal friction in the use of materials, modification and materials in the micro-structure study have an important role; In the nondestructive testing materials, the change of elastic modulus and internal friction is also an important index for judge whether has a defect. Wood as a polymer, anisotropic materials, the wood elastic modulus is an important physical quantity for wood or wood-based materials resist deformation ability. Elastic modulus as an prediction value in the non- destructive wood strength testing, on the study of wood structure design and stability of wood materials is also an important parameter of mechanicalOn the traditional method of the wood materials elastic test, used for the electric resistance strain more. Although, this is a maturity test of mechanical testing methods, but the method of measurement based on the use of limited electric resistance strain guages for test and calculation. Due to wood is porous, flaky and anisotropy of the biological composites, the wood mechanical quatities was measured by the electrical measurement method was unaccurately reflect the mechanics of information, so there is a lot of limitations.Digital speckle correlation method (DSCM) is a computer-aided optical technique for displacement measurement, whose basic principle is based on comparison two digital speckle images taken before and after displacement. It has caught extensive attention and shown favorable development prospects in the recent years, due to its many unique advantages, such as full field measurement, non-contact, and automatic capability, of which other traditional optical methods are lack. In recent years, DSCM, with the advantages of its full-field, non-contact, easy to realize automated access to have a wide range of concerns, has become a sophisticated measurement method, and has been successfully applied to the mechanical measurement. A simple, convenient instantaneous measurement method, have great theoretical and practical value in the evaluation of the wood value, and also have a great guiding significance. In this paper, the use of DSCM measuring three spacies elastic constants, displacement field, and the surface curve fitting. The relationships of elastic constants on orthotropic material are complexed, so, it is need to study on the relationship of anisotropic elastic constants. The results will be tested with inequality of anisotropic materials, the results measured by the elastic constants of wood all meet the above constraints, in all, we can used DSCM to study the mechanical behavior of wood.Wood is a porous layer of composite material, fracture injury usually can be described as a large number of micro-nuclear damage, expansion, connectivity, leading to fracture damage ultimately. Fractal theory as a new subject, it is provide a new mean for stduy on the wood fracture. Fracture surface with a random or statistical sense of self-similar structure is considered to be a fractal structure, its fractal dimension of the fracture surface is the quantitative characterization of different fracture surface .Different dimensions reflect the inherent properties of the material.The fracture of parallel to grain on air-dry wood texture show brittle fracture, and its surface texture with a fractal structure with random or statistical sense of self-similar. When I crack along the axial expansion, due to structural differences between different species and resistance of crack growth (that is, fracture toughness) different, such differences also manifested on the wood-texture of the fracture surface, their have positive correlations between fracture toughness of parallel to grain and fractal dimensions on wood fracture.The experiments showed that the fracture toughness parallel to grain and fractal dimensions of the fracture have highly positive linear relationship: K_IC = 272.42 D -588.45, R² = 0.9831, analysis showed that the macro-construction of wood and micro-mechanical behavior have more relevance, applied fractal dimension characterization of fracture surface to express the capacity crack of wood is feasible, at the same time, fractal theory for studu on the destruction of wood provides a new research tools.