Problem
The Tsai–Hill implementation in src/failure_criterias.jl:32-54 uses incorrect interaction-term denominators. For example, the tensile/tensile branch uses -(σ1/Xt)*(σ2/Xt) rather than the usual sign-dependent -σ1σ2/(X·Y) form. Other branches similarly use Xc in the cross term even when the transverse allowable is Yt or Yc.
Engineering consequence
Failure indices for biaxial states can be substantially over- or under-predicted, particularly for highly orthotropic plies where longitudinal and transverse strengths differ by orders of magnitude. This undermines Tsai–Hill results under combined loading.
Proposed improvement
Implement the selected Tsai–Hill convention explicitly using the appropriate longitudinal and transverse tensile/compressive allowables for each stress-sign quadrant. Document the exact equation and convention, including whether the criterion is intended as the classical Hill form or a particular composite adaptation. Add hand-calculated tests for all four sign quadrants and pure σ1, σ2, and τ12 loading.
Problem
The Tsai–Hill implementation in
src/failure_criterias.jl:32-54uses incorrect interaction-term denominators. For example, the tensile/tensile branch uses-(σ1/Xt)*(σ2/Xt)rather than the usual sign-dependent-σ1σ2/(X·Y)form. Other branches similarly useXcin the cross term even when the transverse allowable isYtorYc.Engineering consequence
Failure indices for biaxial states can be substantially over- or under-predicted, particularly for highly orthotropic plies where longitudinal and transverse strengths differ by orders of magnitude. This undermines Tsai–Hill results under combined loading.
Proposed improvement
Implement the selected Tsai–Hill convention explicitly using the appropriate longitudinal and transverse tensile/compressive allowables for each stress-sign quadrant. Document the exact equation and convention, including whether the criterion is intended as the classical Hill form or a particular composite adaptation. Add hand-calculated tests for all four sign quadrants and pure σ1, σ2, and τ12 loading.