Firehole News 
What’s So Big about Progressive Failure Analysis? July 2011
Advances in Composite Simulation
3 Reasons to Consider Composite Progressive Failure Analysis
It’s true. Not every design program will need progressive failure analysis. If your application must be conservative to account for unknown loading conditions and has zero tolerance for degradation, first ply failure may be right for you. If you do not need to optimize your design to be the most efficient or target a specified amount of margin, first ply failure may be right for you. Otherwise, take a look at these reasons to consider composite progressive failure analysis.
1. Under-Predicting or Over-Predicting? - What You Don’t Know Can Hurt You
Linear, first ply failure methods smear the constituent properties to evaluate a homogenized lamina against a selected failure criterion. Such an approach dilutes the contributions of the constituents, including the fiber’s contribution to longitudinal tensile strength and the matrix’s contribution to all other composite strengths. The result can be a significant under-prediction in some load cases and over-prediction in others.
2. First Ply Failure Masks Failure Mode
Imagine you need to evaluate three different design options (geometry, layup, etc.) for a composite component. You would like to virtually test the designs using Finite Element Analysis to determine which design option is the most promising. Is First Ply Failure sufficient?
The models at right show the results of using the widely held Tsai-Wu failure criterion in a First Ply Failure analysis. First Ply Failure occurs at the same displacement and same location for each option, providing no decision-enabling information. Test results reveal each of these options will experience a different failure mode – two are catastrophic. Is it possible for Finite Element Analysis to provide results that more closely predict such outcomes? The answer is yes. See how a progressive failure analysis stacks up.
3. How Do the Plies Interact? First Ply Failure Precludes Inter-laminar Effects
Does your analysis need to consider delamination or debonding? A traditional First Ply Failure approach simply uses selected failure criteria to determine the first instance of degradation in a ply of the laminate. But what happens after the onset of matrix cracking? How is the bond affected? A progressive failure analysis that combines in-plane and out-of plane simulation can provide this insight.