A NONLINEAR STRENGTH CRITERION AND TRANSFORMATION STRESS METHOD

The curve is expressed by a power parameter curve in the space of normal stress and shear stress. The outer tangent point of the curve and the mohr's circle corresponds to the point of failure stress point. Then, the inverse tangent value of the slope of the outer tangent line at the point is used to obtain the effective slip Angle.There are three effective slip angles for a three-dimensional element, and three effective slip angles are used to determine the effective slip surface of space. Based on the basic features of geotechnical materials as friction materials, the stress ratio on the effective slip surface is taken as a certain value to judge whether the material is damaged or not. The t strength criterion was derived based on the above ideas, in deviatoric plane, the shape of t criterion is a closed curve between Von-Mises criterion and SMP criterion. In the meridian plane, the introduction of open power function as a reflection of the curve of the effect of hydrostatic pressure and shear failure, and closed droplet type yield criterion function is adopted to reflect volume compression yield curve, reflect the compression-shear coupling characteristics of geotechnical material. Based on the proposed t strength criterion, the transformation stress formula is derived, which can easily transform the two-dimensional model by using p and q as the stress variables into a three-dimensional stress state constitutive model. Through the test and comparison of strength and various stress paths, the rationality of the proposed t criterion and the transformation stress formula based on the criterion is verified.