Maximum stress criterion (3D)

II.1.10.5 Maximum stress criterion (3D)

The failure index is calculated as follows:

F I^{MaxStress3D} = max (| \frac{σ_{11}}{σ_{11}^{all}} |, | \frac{σ_{22}}{σ_{22}^{all}} |, | \frac{σ_{33}}{σ_{33}^{all}} |, | \frac{τ_{12}}{τ_{12}^{all}} |, | \frac{τ_{23}}{τ_{23}^{all}} |, | \frac{τ_{31}}{τ_{31}^{all}} |),

in which the $σ_{11}^{all}$ , $σ_{22}^{all}$ and $σ_{33}^{all}$ allowables depend on the sign of $σ_{11}$ , $σ_{22}$ and $σ_{33}$ respectively. (Generally, tensile and compressive allowables are different for orthotropic materials.) Ply passes the test if the six following conditions are satisfied:

| σ_{11} | \leq σ_{11}^{all},

| σ_{22} | \leq σ_{22}^{all},

| σ_{33} | \leq σ_{33}^{all},

| τ_{12} | \leq τ_{12}^{all},

| τ_{23} | \leq τ_{23}^{all},

| τ_{31} | \leq τ_{31}^{all} .

The reserve factor is calculated as follows:

R F^{MaxStress3D} = \frac{1}{F o S \cdot F I^{MaxStress3D}},

and the strength ratio is given by:

S R^{MaxStress3D} = F o S \cdot F I^{MaxStress3D} .

This criterion is referred to as “MaxStress3D” criterion in FeResPost.

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