Failure Criteria
The CLT tool evaluates twelve composite failure criteria organized into four families. Each criterion computes a Margin of Safety (MS) for every ply at every through-thickness location.
Independent Criteria
Maximum Strain
Independent ε₁, ε₂, and γ₁₂ strain checks. The margin is the minimum across all three strain components, with tension and compression allowables selected based on the sign of the strain.
Maximum Stress
Independent σ₁, σ₂, and τ₁₂ stress checks. Stress allowables are derived from strain allowables using the appropriate directional moduli.
Interaction Criteria
Tsai-Hill
Quadratic strain interaction criterion. Uses signed tension/compression strain allowables based on the current strain state. The interaction term couples fiber-direction and transverse strains.
Tsai-Wu
Tensor-polynomial stress interaction criterion with the cross-term F₁₂ = −½√(F₁₁F₂₂). Accounts for different tension and compression strengths through linear stress terms.
Hoffman
Quadratic stress interaction with cross term σ₁σ₂/(X·Y) using signed strengths. Similar to Tsai-Wu but with a different interaction coefficient.
Mode-Separated Criteria
Hashin
Separates failure into four distinct modes: fiber tension, fiber compression, matrix tension, and matrix compression. Each mode has its own failure surface with shear coupling.
Puck (IFF)
Fiber failure plus inter-fiber failure on the action plane with three matrix failure modes (A, B, C). Uses default CFRP inclination parameters per VDI 2014.
LaRC03
NASA LaRC criterion: fracture-plane matrix compression (α₀ = 53°) with Mohr-Coulomb friction, Hashin-type matrix tension. Accounts for in-situ effects.
Christensen
Separated fiber (max stress) and matrix (quadratic σ₂/τ₁₂ polynomial) failure modes per Christensen (2013).
Principal Criteria
Max Principal Strain
Maximum principal strain compared against the most conservative ply strain allowable across all plies.
Max Principal (Outer)
Max principal strain evaluated only at outer mold line surfaces (ply 1 top, last ply bottom).
Max Principal Stress
Maximum principal stress compared against the most conservative ply stress strength.