Laminate Composites > Laminates theory > Laminates failure analysis
Tsai-Wu failure analysis (2D)
Failure Index
The expression of the Tsai-Wu failure criterion is:
Where F is the failure index and:
In the absence of test data, the following is recommended for defining the Tsai-Wu interaction coefficient, F12 [1, 2]:
The software performs the following stability check:
If the stability check passes, the software uses the user-defined value for F12. If the stability check fails, the software uses F12 = 0.0.
For other variable definitions see Laminate failure analysis nomenclature.
Margin of Safety
To calculate the margin of safety for the Tsai-Wu failure criterion, we must first determine the value of the proportionality factor α such that the state of stress given by ασ1, ασ2, and ατ12 gives a failure index F of 1. To calculate the value of α, we rewrite the first equation in this section:
Which is a quadratic equation in α that can be rewritten:
Where:
The solutions to this quadratic equation are:
The software takes α to be the smallest positive value between α1 and α2. If both α1 and α2 are negative, α is set to zero. It calculates the margin of safety, MS, as follows:
MS = (α/FS – 1) X 100
Strength Ratio
The strength ratio, SR, is the proportionality factor α:
SR = α
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Tsai-Wu failure analysis (2D), Simcenter 3D 2021.1 Series
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Source: https://docs.sw.siemens.com/en-US/doc/289054037/PL20200601120302950.advanced/id626801 · retrieved 2026-07-17