Let the failure strength in uniaxial tension and compression in the three directions of anisotropy be σ σ 1 t , σ σ 1 c , σ σ 2 t , σ σ 2 c , σ σ 3 t , σ σ 3 c . Also, let us assume that the shear strengths in the three planes of symmetry are τ τ 23 , τ τ 12 , τ τ 31 (and have the same magnitude on a plane even if the signs are different). Then the coefficients of the orthotropic Tsai–Wu failure criterion are