Abstract
Based on the postulate of stability of materials failure criteria of macroscopically homogeneous isotropic brittle materials under combined stresses are represented by convex surfaces in the principal stress space.
The failure surfaces of both high- and low-strength concretes were compared in the compression rarge as the maximum first stress invariant up to 5.2 times of the uniaxial compressive strength.
The surfaces of the both concretes are almost identical when they are represented in the non-dimensional principal stress space, though their absolute values are quite different.
The surfaces are convex and have the space diagonal as a threefold rotation axis.
Right sections of the surfaces are slightly bulged from equilateral triangles and expand almost isotropically with a decreasing ratio as the hydrostatic pressure increases.
