Maximum Stress Criterion
Failure Criterion
The maximum stress criterion applies to composite shells.
Failure occurs according to the maximum stress criterion when the stress
in one of the principal material directions exceeds the strength in that
direction. The overall state of stress in the global coordinates is first
computed by the program. Then, the program computes stress along the principal
material directions for each lamina by applying a coordinate transformation.
The program assumes a state of plane stress (2D assumption) for a lamina
with s3 =0, t13 =0, t23 =0. The failure index is computed
as follows:
The program reports the factor of safety (FOS)
as 1 / (F.I.). The FOS should be greater than 1 for laminates to be safe.
where:
X1 is the tensile strength in material
direction 1
X2 is the tensile strength in material
direction 2
S12
is the shear strength
Click principal material directions
for a definition of material directions 1 and 2.
Further,
X1 = X1T if s1 > 0
X1
= X1C if s1 < 0
X2
= X2T if s2
> 0
X2
= X2C if s2 < 0
Superscripts T
and C denote tensile and compressive
strengths.
Notes:
The maximum stress criterion:
Does not take the interactions between different
stress components into account as seen from the above equations.
Predicts specific failure
modes since stress in each material principal direction is compared with
strength in that direction.
Related Topics
Performing
factor of safety check
Guidelines
for Selecting a Failure Criterion
Composite
Failure Criteria