normal or shear stresses acting on the faces of a three-dimensional octahedron which has geometric property that the faces of the planes make equal angles with each of the three principal directions of stress, pinged (normaal- ja nihkepinged), mis toimivad kolmemõõtmelise oktaeedri tahkudel, omavab geomeetria, kus tasanditahud on võrdse nurga all kolme põhipinge suundadega peatelgede suhtes