Layered composites are typically made of various materials (reinforced plastics, foams, and honeycomb, for example) which often have an orthotropic characteristic. Composite postprocessing in the Mechanical application takes this into account. The Mechanical software implements many different failure criteria which are applied to specific materials. For instance, Puck evaluates the safety margin for uni-directional materials (UD) only where Max Stress is applied to UD and weave materials. The table Failure Criteria vs. Ply Type explains the relationship between specific failure criteria and material types. Also, the different failure criteria account for the numerous possible failure modes (fiber failure, delamination, and wrinkling for example) in layered composites. (See Failure Criteria Overview in the Composites Theory Reference.)
In the Mechanical application, you can easily combine failure criteria. This allows you to postprocess and optimize complex layered composites efficiently because the most critical failure value and failure mode are readily accessible. For additional background information on composite postprocessing, see Failure Analysis and Interlaminar Stresses.
An alternative to postprocessing in the Mechanical application is the PyDPF Composites module, which is based on the same postprocessing engine as the Mechanical application. Therefore, it implements the same failure criteria and features, while also providing more flexibility. The PyDPF Composites module is commonly used for:
Scripting-based postprocessing in a pure Python environment (without a graphical user interface)
Customization of the postprocessing (for instance, the implementation of custom failure criteria)
Postprocessing of models that were not preprocessed in the Mechanical application (such as .rst files from the Mechanical APDL application)
For more information on PyDPF Composites, see Getting started and Examples.
Note: Composite postprocessing in the Mechanical application computes the most critical failure and does not estimate any residual strengths, subsequent failures, or stress redistribution. This method is also called first ply failure (FPF). In other words, it assumes the laminate fails when the first ply fails. Therefore, composite postprocessing is not suitable for any solution (such as impact or damage analysis) which goes beyond FPF. For a list of analysis that composite postprocessing supports, see the section on Supported Analysis Types. The opposite of an FPF analysis is a final failure analysis which is part of a progressive damage or explicit analysis, both of which are supported by Ansys products.
This chapter covers: