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Predicting Defect Formation at Early Stages of Manufacturing Process



Combination of wrinkles and voids are common manufacturing defects in laminated composite components and structures. In particular, composite helicopter rotor components are typically thick and often have areas with tight radii of curvature, making them especially prone to process-induced defects. Wrinkles and voids may significantly affect structural integrity and increase rejection rates in the production of rotor composite components. Recent advances in high-fidelity non-destructive inspection of composites, such as X-ray Computed Tomography (CT), have shown that reduction of strength and fatigue performance of laminates can be strongly related to shape, size, and location of critical individual defects. However, none of the existing tools available for process modeling are able to predict the formation of such individual defects, including their geometry and position in the composite parts. This work is part of the Office of Naval Research (ONR) project “Physics-Based Composite Process Simulation” that seeks to fill the gaps in understanding the underlying physical principles governing the formation of manufacturing defects. In particular, there is strong evidence that improper laminate consolidation at early stages of the laminate manufacturing process, including debulking or vacuum consolidation, is one of the major root causes for both wrinkle and void formation in autoclave composites. Therefore, understanding and modeling defect formation at the early stages of the manufacturing process might be the missing link to enable development of practical engineering solutions for better control of the manufacturing process This work presents the latest developments of a simulation method for predicting defect formation during vacuum consolidation using discrete modeling of the large pockets of entrapped air at ply interface in resin-saturated autoclave tape prepregs. Experimental procedures developed for measuring critical input data used in the numerical models and the fabrication of a rotor blade grip test element for verification of applicability of the method are also presented.


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