13.1.3.2. User-Written Failure Criteria
You can specify user-written failure criteria via user subroutine USERFC. This subroutine should be
linked with the program beforehand. For more information, see User-Programmable Features and
Nonstandard Usesin the Advanced Analysis Guide.
13.1.4. Composite Modeling and Postprocessing Tips
Following are a few helpful hints and tips for modeling and postprocessing composite elements:
13.1.4.1. Dealing with Coupling Effects
13.1.4.2. Obtaining Accurate Interlaminar Shear Stresses
13.1.4.3. Verifying Your Input Data
13.1.4.4. Specifying Results File Data
13.1.4.5. Selecting Elements with a Specific Layer Number
13.1.4.6. Specifying a Layer for Results Processing
13.1.4.7. Transforming Results to Another Coordinate System13.1.4.1. Dealing with Coupling Effects
Composites exhibit several types of coupling effects, such as coupling between bending and twisting,
coupling between ext ension and bending, etc. This is due to stacking of layers of differing material
properties. As a result, if the layer stacking sequence is not symmetric, you may not be able to use
model symmetry even if the geometry and loading are symmetric, because the displacements and
stresses may not be symmetric.
13.1.4.2. Obtaining Accurate Interlaminar Shear Stresses
Interlaminar shear stresses are usually important at the free edges of a model. For relatively accurate
interlaminar shear stresses at these locations, the element size at the boundaries of the model should
be approximately equal to the total laminate thickness. For shells, increasing the number of layers per
actual material layer does not necessarily improve the accuracy of interlaminar shear stresses. Interlam-
inar transverse-shear stresses in shell elements are based on the assumption that no shear is carried at
the top and bottom surfaces of the element. These interlaminar shear stresses are only computed in
the interior and are not valid along the shell element boundaries. Use of shell-to-solid submodeling is
recommended to accurat ely compute all of the free edge interlaminar stresses.
13.1.4.3. Verifying Your Input Data
Because a large amount of input data is necessary for composites, it is a good idea to verify the data
before proceeding with the solution.The following commands are available for this purpose:
- ELIST -- Lists the nodes and attributes of all selected elements.
- EPLOT -- Displays all selected elements. Using the /ESHAPE,1 command before EPLOT causes shell elements
to be displayed as solids with the layer thicknesses obtained from real constants or section definition (see
Figure 13.5: Example of an Element Display (p. 415). - /PSYMB,LAYR,n followed by EPLOT -- Displays layer number n for all selected layered elements. Use this
method to display and verify each individual layer across the entire model. To use /PSYMB,LAYR with
smeared reinforcing elements (REINF265), first set the vector-mode graphics option (/DEVICE,VECTOR,1). - /PSYMB,ESYS,1 followed by EPLOT -- Displays the element coordinate system triad for those elements
whose default coordinate system has been changed.
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