岩石材料の粘塑性と直接せん断試験

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The rock-type materials in general show a definite irreversible deformation above a certain stress state. It is a well known fact that under large confining pressure or high temperature they behave as plastic and viscoplastic materials under loading. This type of behavior is called ductile deformation, and may be explained by the dislocation theory. On the other hand. the rock-type materials show another kind of irreversible deformation under relatively low confining pressure or temperature. This may be called brittle irreversible deformation mainly caused by grain boundary separations and crack development in grains. Generally, the ductile deformation is accompanied by no volumetric change, but the volumetric expansion is common in the brittle deformation. It is not easy to construct such constitutive equations of the material as well explain the whole behavior of the material. In this paper. the constitutive equations which describe these two irreversible deformations are derived from the 2nd law of thermodynamics. As initiative step to evaluating the constitutive equations, the direct shear test was conducted by measuring the shear and the normal displacements u_x and w_z, respectively. By plotting log u_z and log w_z, with respect to the average applied shear stress τ for various normal pressure p_o, we find four characteristic points. By these characteristic points in the τ vs. p_o diagram, the various zones of the stress states are defined, elastic, viscoplastic. stable brittle. unstable brittle and failure states. The constitutive equations for ductile deformation may be applicable to the viscoplastic state, while that for brittle one to stable brittle state. It may also be said in conclusion that the ductile yield function does not necessarily depend on the mean stress as the brittle yield function does. Finally, we find that the relation between the strain rate and the applied stress of the viscoplastic component of the material behavior is expressed by the power function φ=(τ_0/K_0-1)^n and with n=2.6 obtained for halite.
社団法人日本材料学会の論文
1971-02-15

岩石材料の粘塑性と直接せん断試験

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