The Tsai–Hill failure criterion is one of the phenomenological material failure theories, which is widely used for anisotropic composite materials which have different strengths in tension and compression. The Tsai-Hill criterion predicts failure when the failure index in a laminate reaches 1.
Tsai–Hill failure criterion in plane stress The Tsai-Hill criterion is based on an energy theory with interactions between stresses. Ply rupture appears when:
( σ 11 X 11 ) 2 − ( σ 11 σ 22 X 11 2 ) + ( σ 22 X 22 ) 2 + ( τ 12 S 12 ) 2 ≥ 1 {\displaystyle {\begin{aligned}\left({\cfrac {\sigma _{11}}{X_{11}}}\right)^{2}-\left({\cfrac {\sigma _{11}\sigma _{22}}{X_{11}^{2}}}\right)+\left({\cfrac {\sigma _{22}}{X_{22}}}\right)^{2}+\left({\cfrac {\tau _{12}}{S_{12}}}\right)^{2}\geq 1\end{aligned}}}
Where:
X 11 {\displaystyle {\begin{aligned}X_{11}\end{aligned}}} is the allowable strength of the ply in the longitudinal direction (0° direction)
X 22 {\displaystyle {\begin{aligned}X_{22}\end{aligned}}} is the allowable strength of the ply in the transversal direction (90° direction)
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