Investigations on Transport Phenomena Governing Interfacial Bonding Evolution in Thermoplastic Composites

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Thermoplastic-matrix composites are fabricated by incrementally stacking andfusion-bonding layers of fiber-reinforced thermoplastic prepreg tapes to adesired shape and thickness. The evolution of interlaminar bond strength---aprincipal product quality measure---is governed by the development ofinterfacial contact area through flattening of the prepreg surfaceasperities (referred to as the "intimate contact" process), and theinterdiffusion of polymer molecules across the contacted areas (termed"healing"). The geometric complexities of the surface asperity structures,and the mechanistic complexities of the strongly coupled microscaleprocesses of "intimate contact" and "healing" pose a fundamental challengeto a reliable description of interfacial bonding evolution duringprocessing. The overall goal of the project is to overcome theseimpediments. The inherent geometric complexities of the microscale will berendered tractable using an innovative fractal representation of surfaceasperity profiles. This will form the basis of microscale transportphenomena models to be developed for describing the asperity spreading andpolymer interdiffusion processes. A coupling of the microscale processdescription with the macroscale heat and momentum transport phenomena modelswill be used to elicit a comprehensive understanding of interfacial bondingdevelopment as function of the process parameters. Complementaryexperimental studies will be conducted aimed at validating the theoreticaldevelopments.