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Multiscale Progressive Failure Prediction of Laminated Composites
PI: Anthony M. Waas
Collaborator: Dr. Brett Bednarcyk, NASA-Glenn RC
Particpant: Evan Pineda

Several important studies have shown the weight specific advantages of composites in structural applications. However, studies related to demonstrating certain aspects of damage tolerance are still ongoing. A complete understanding of damage tolerance, both from an experimental and analytical view point is necessary to fully exploit the weight savings that can be realized by using composites in aerospace structural applications.

Distinctions between the various damage and failure mechanisms that manifest during the loading of composite materials must be apparent. In epoxy matrix composites, highly distributed microcracks grow as the structure is loaded, effectively reducing the elastic moduli of the material. This type of progressive damage is seldom accounted for in current analyses, but remains the dominant cause of nonlinearity in the stress-strain response of a composite up to the onset of larger transverse cracks.

Furthermore, the unidirectional laminated composite is itself a structure involving matrix, fibers, and the fiber-matrix interface. The globally observed damage mechanisms that arise are, in fact, a result of the interaction between the damage and failure mechanisms within each of the constituents. Efforts must be made to investigate the effects of the composite microstructure on the overall behavior of the global structure.

The Aerospace and Mechanical Engineering departments at the University of Michigan are working in collaboration with NASA, and the Collier Research Corporation to develop a completely robust, multiscale physics based prediction and design tool for composite structures that is capable of performing sophisticated analyses while remaining user friendly and requiring minimal amounts of coupon level data to define material behavior. At the largest length scale, Level 1, entire structures are analyzed using the commercially available software, Hypersizer. Load predictions and sizing analyses are performed at this level using information from Levels 2 and 3. At the second largest length scale, Level 2, progressive microcracking is modeled at the lamina level using Schapery Theory. Finally at Level 3, the MAC/GMC suite of micromechanics codes developed by NASA is used “on the fly” to refine stress and strain fields to the microconstituent level using information from Levels 1 and 2. Micro-mechanical analyses can be executed at Level 3 and data can be passed back to Levels 1 and 2. Furthermore, MAC/GMC is used for micro-mechanical preprocessing analysis to obtain inputs for the other two levels.

This project is supported through sponsorship from NASA Langley through the Colllier Corporation.

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