Properties Of Material Mechanical With Crystalline Shape Coefficients And Digital Images Measurement

The metal sheet is a polycrystal composed of a large number of small crystal-grain at mesoscopic level. The crystalline shape, usually manifesting irregularity, is one of the characteristics of crystalline. Effects of crystalline shape and orientation on mechanic properties of materials are the focus of people’s attention in the study of metal material’s elastic properties. The study of macro and meso-properties are mostly based on the Taylor hypothesis. This paper begins by describing grain shape and the research includes elastic constitutive relationship of crystalline shape effect; based on crystalline size, the paper investigates the relationship between metal materials’macro, meso-mechanical properties by adopting the analysis method of digital imaging.In the paper, crystalline shape function(CSF), which represents crystalline shape, can be expanded into series form in the Wigner D-function where the expanded coefficients are called shape coefficient; researches the impact of average crystalline shape on the elastic constitutive relationship of the orthogonal polycrystalline grain, obtaining a new expression of the elastic constitutive relationship Cijkleff of polycrystalline materials which includes the crystalline shape effect; perturbation method is used to estimate the undetermined material constant of the new constitutive expression and then finite element method and self consistent method are used to test the new constitutive expression Cijkleff.In this paper, the analysis technique of digital imaging is adopted on the parametric study of irregular crystalline shapes. The multi-chord method of minimum bounding rectangle, ellipse and segmented crystalline gain is used to make a parametric description for the target crystalline grain based on extracting the accurate crystalline boundary. It is found that when crystalline shapes are particularly irregular, ellipse fitting and minimum bounding rectangle fitting are upper and lower limits respectively for crystalline shape parameters whereas the fitting results of seven string method are rather reasonable. The results of experimental research on the evolution of target crystalline shapes in metal materials based on crystalline parameterization show that:crystalline shape parameters-slenderness ratio’s numerical values are consistent with the theoretical results of macro-mechanical properties in both the elastic and plastic stage.The paper adopts the digital speckle image correlation method and the traditional electrical measuring method in the experimental measurement and computational study of crystalline grain’s local strain and macroscopic strain in metal sheets after obtaining digital images of clear crystalline boundaries and complete crystalline grains. Experimental measurement of microcosmic strain in crystalline size is achieved by using digital speckle image correlation method to examine the microscopic digital images of crystalline grains. The experimental results show that the average local strain of crystalline grains is in good agreement with the macroscopic strain of materials, which verifies the Taylor hypothesis.Finally, an easy-to-use digital speckle correlation method with simple test equipment is developed to measure the mechanical properties of large strain materials through a self-compiled CCP program.