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In true triaxial stress state, followed by a 45o shear failure of three groups face is six-sided unit body unit of the interception is orthogonal octahedral unit body. The unit body is not only the basis of the theoretical system of generalized octahedron (Yang Jianhui, 2007), but also the basis of the analysis unit twin shear strength theory. Orthogonal octahedral unit on stress is shear stress transformation the dual shear stress and stress Lode parameter (including contingency Lode parameter), twin shear stress contains intermediate principal stress and hydrostatic stress effect, and in the strength The adaptability of the model has been proved, thus the double shear stress has clear physical meaning and rich content. Constructed according to the strength of the model of the twin shear strength theory, namely polynomial strength model, in terms of the mathematical theory that such a strength model uncertainty, but according to the characteristics of the twin shear stress boundary conditions (characteristics of test points that uniaxial tensile and compressive strength, biaxial, triaxial pull compressive strength of six characteristics of the test points), the rank of the equations of full rank and practical problems, their model is the uncertainty of a few, giving the research bring the convenience and applications. Can derive a characteristic test point parameters intensity model by using different boundary conditions, respectively, can be simplified to the third strength theory and Mohr-Coulomb theory, as well as unknown strength model, and are given the appropriate adaptation condition. Significance based on mathematical equations full rank, established by the four-parameter strength model plane characteristic strength parameter relations equation, biaxial and triaxial characteristic strength parameters between equations; while all six characteristics of strength by six parameters intensity model The parameters of the relationship equation; also gives simple and practical calculation process the multiaxial strength model has universal applicability. By this calculation process, even in the case of only uniaxial tensile and compressive strength test values ??of the two characteristic can still deduce the value of the ultimate strength of the stress values ??of all features, and arbitrary loading conditions. Space on any oblique plane stress analysis and strain analysis principle, orthogonal octahedron strain constitutive equation. Isotropic linear elastic body, established orthogonal octahedron strength - deformation constitutive relations. Orthogonal octahedral symmetry and any one surface with one of a Cartesian coordinate axis parallel to the characteristics, thus, the simple spatial problem can be converted to a plane problem studied. The use of double-shear strength model has a rich interpretation of the characteristics of the specific model of strength interpretation promotion, through the interpretation of the multiple limit on π plane traces, the model indicates that strong adaptability. Finally, the intensity of the resulting model, the use of some of the test data on the open literature, the model is validated, the result indicates that the model is reasonable.
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