GOALI: Inter-Laminar Toughening of Composite Structures: Bonding Mechanisms and Delamination Resistance

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This Grant Opportunity for Academic Liaison with Industry (GOALI) research project investigates a novel process for the inter-laminar toughening of polymer matrix composites. The need to toughen composite structures arises from the preferential planar fiber/matrix brittle de-bonding (delamination). The method aims to locally integrate a tough thermoplastic polymer interleaf between fiber fabric plies near each existing stress concentration site by intimately bonding it to the plies and the thermoset epoxy matrix. The intimate bonding is achieved through (1) hot melt bonding the thermoplastic interleaf with fibers to deeply encapsulate the fibers, and (2) diffusively bonding it with the thermoset matrix in the subsequent vacuum assisted resin transfer molding curing. Analysis will yield significant insights into the coupled effects of fiber-interleaf and interleaf-matrix bonding on the fracture toughness and delamination resistance of preform composites. Investigation into the interface resolved wetting and viscous flow behaviors as well as thermoset-thermoplastic inter-diffusion kinetics will elucidate interactions underlying these bonding mechanisms. The expected results from this project will develop new directions for the design and fabrication of more efficient composite components with greater delamination resistance. The PI's close interaction with a key industrial partner will lead to the rapid development of the thermoplastic interleaving method through application-specific laminate fabrication and testing, leading to greater competitiveness of an important renewable energy source and thus broader societal impact. If the toughness of large, tapered laminate composites such as wind turbine blades is enhanced, longer blades and taller wind turbines will help reduce cost, spread wind energy usage, and reduce environmental impact. Process knowledge and modeling developments gained from this work may be extended to a wide range of material fabrication techniques such as dissimilar materials joining and sealing: thermoset-thermoplastic matrix composite bonding, and thermoset matrix composite to metals bonding.