The Hill criterion for orthotropic materials predicts material failure according to the following quadratic function:
 | (2–1) |
where 
are the stress components, and the corresponding stress limits are
given here in Equation 2–2. (See also
equation 3-64 in the section 3.3.1.2. Hill Yield Criterion of the Material Designer User's
Guide.)
 | (2–2) |
The stress ratios 
are those specified in the Hill Yield Criterion,
while 
is the isotropic Tensile Yield Strength.
The definition of the stress limits in the Hill criterion is often modified to account for the different behavior in tension and compression, which is then usually referred to as the Tsai–Hill criterion. In such case, the formulation (Equation 2–1) remains unchanged, but the stress limits are those stored as Orthotropic Stress Limits in Engineering Data:
|
The following combination of failure criteria and material properties are available for short fiber composites: