Mechanical APDL Structural Analysis Guide

Figure 13.4: Layered Shell With Nodes at Bottom Surface

13.1.3. Specifying Failure Criteria for Composites

Failure criteria are used to learn if a layer has failed due to the applied loads. You can choose from
three predefined failure criteria or specify up to six failure criteria of your own (user-written criteria).
The predefined criteria are:

• Maximum Strain Failure Criterion-- Allows nine failure strains.


• Maximum Stress Failure Criterion -- Allows nine failure stresses.


• Tsai-Wu Failure Criterion -- Allows nine failure stresses and three additional coupling coefficients.

The failure strains, stresses, and coupling coefficients may be temperature-dependent. For details about
the data required for each criterion, see the Element Reference.

Failure criteria are orthotropic, so you must input the failure stress or failure strain values for all directions.
( The exception is that compressive values default to tensile values.)

If you do not want the failure stress or strain to be checked in a particular direction, specify a large
number in that direction.

The following topics for specifying failure criteria for composites are available:

13.1.3.1. Using the FC Family of Commands

13.1.3.2. User-Written Failure Criteria

For more information, see Failure Criteria in the Mechanical APDL Theory Reference.

13.1.3.1. Using the FC Family of Commands

To specify a failure criterion, use the family of FC commands. These FC commands can be used for any
2-D or 3-D structural solid element or any 3-D structural shell element:FC,FCDELE, and FCLIST.

A typical sequence of commands to specify a failure criterion using these commands follows:

FC,1,TEMP,, 100, 200! Temperatures

FC,1,S,XTEN, 1500, 1200! Maximum stress components

FC,1,S,YTEN, 400, 500

FC,1,S,ZTEN,10000, 8000

FC,1,S,XY , 200, 200

FC,1,S,YZ ,10000, 8000

FC,1,S,XZ ,10000, 8000

FCLIST, ,100! List status of Failure Criteria at 100.0 degrees

FCLIST, ,150! List status of Failure Criteria at 150.0 degrees

FCLIST, ,200! List status of Failure Criteria at 200.0 degrees

PRNSOL,S,FAIL! Use Failure Criteria

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Modeling Composites