²ÝÝ®ÊÓƵ

This study is in partnership with Computational Engineering Software, LLC ().

Critical damage within metallic structure usually takes the form of cracks. The main issue is continued growth of the cracks as a function of in-service loading conditions. Often crack growth due to cyclic loading is of interest. Damage within composite structure has a higher number of factors to represent how critical the damage is. It must be considered that:

• Single cracks rarely exist in composite laminates, if they exist do it is usually as a delamination between adherents.
• Damage usually manifests itself as a network of inter-connected delaminations and transverse cracks.
• Unlike metals, Fracture mechanics is generally not applicable to laminated damage. The Mode I, Mode II and Mode III single crack failure modes require satisfaction of similitude to be realized in composite structures.

The main question to be answered is this study is when will the damage perimeters begin to grow under operational cyclic load. To do that, we expect to accomplish the following main steps:

Obtain limiting critical values for one or more material systems.

Develop a sequence of tests to simulate damage and then measure limits to catastrophic failure in compression and/or tension.

Model each of the test articles and apply the Onset approach to predict whether (for a given applied loading environment) the damage will or will not begin to propagate.

Compare prediction of the onset of propagation to measured ultimate failure. The criterion of success is that the numerical methodology can conservatively, but realistically predict a load level below which propagation does not occur.