土質材料における変形の多価性とせん断帯の形態

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The volumetric change accompanying with plastic shear deformation causes the dependency of q on p where p and q respectively represent the hydrostatic pressure and equivalent deviatoric stress in yielding. Their dependency is called yield curve or yield function. For predicting yield curve the following assumptions are set up. Yield curves expand similarly in shape with plastic deformation and yield function plays as a plastic potintial. Basic yield curve is determined which gives a basic shape in similary expansion of yield curve. Using experimental results obtained under plane strain compression tests, we predict the basic yield curves. The basic yield curve has a limit over which yield curve cannot expand in (p, q) space. We call it expanding limit. First, it is examined whether plastic instability arises or not in plane strain compression tests, but its occurrence is denied consequently. Next, we show that multiple deformation rate can exist at the expanding limit. Hence, the onset of bifurcation is predicted at the expanding limit and the mode of shear plane is determined based on the concept of a characteristic plane. These predictions agree reasonably well with reported experimental observations.