Lightweight, High Performance Composites – Using FEA to Predict the Gradual Failure of Adhesives

Question: How can FEA be used to model the gradual failure of adhesives in composites?

Answer: You use the cohesive zone modeling technique.

Here is quick explanation of CZM from Andrew Main’s Use of Finite Element Analysis to Create Robust Composite Designs – Going Beyond First Ply Failure.

Unlike virtual crack closure, cohesive zone modeling uses an interface element to model t he adhesive joint that is failing. This gives the advantage that we can have a failure model for the adhesive which allows a gradual release. This is suitable for flexible adhesives. Figure 8 shows a typical stress/strain plot for a cohesive material. The area under this represents the “cohesive energy” or critical energy release rate.

Figure 8. Cohesive Material stress/strain curve

This failure modeling approach is more appropriate for a non-brittle failure mode, which may be more common than we think! Epoxy resins do show a visco-elastic behavior which is not really brittle.

Watch a webinar on modeling composites. Jump to 32:40 for more on CZM.

Want to expand your knowledge?

• Watch a YouTube playlist on Composite Material Analysis.
• Watch a YouTube webinar titled Failure Analysis of Composite Structures.
• Watch a YouTube webinar titled Progressive Ply Failure Analysis of Advanced Composites.
• Watch a YouTube webinar titled Modeling Composites with MSC Nastran.

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