All ETDs from UAB

Advisory Committee Chair

Uday k Vaidya

Advisory Committee Members

J Barry Andrews

Kathryn Brannon

Derrick R Dean

Gregg M Janowski

Mark L Weaver

Document Type


Date of Award


Degree Name by School

Doctor of Philosophy (PhD) School of Engineering


Thermoplastic composites have found increasing use in transportation, military, and aerospace applications. Specifically, long fiber thermoplastics (LFT) have become well established as medium performance, high volume, and low cost materials due to high level of productivity in processing. The mechanical properties of LFT components are defined by the fiber / matrix system and also, to a large extent, by the process-induced flow orientation and fiber lengths. The orientations and fiber length are influenced significantly by the flow characteristics, processing method, and parameters. This work focuses on the rheological characterization of LFT processed via the extrusion-compression molding technique. The squeeze flow technique has been adopted to characterize the flow behavior under isothermal conditions. A transversely isotropic power-law model has been incorporated to capture the combined effect of shear and extensional flow behavior. The effects of temperature, fiber length, and fiber weight fraction of the flow characteristics were analyzed. This work was followed by process simulation of the extrusion-compression molding technique on a mass transit component. Process simulation was conducted to evaluate the flow of fiber-filled viscous charge during the molding process. Studies on iv optimum charge size and placement in the tool, press force, shrinkage, and warpage were also conducted. The predictions of molten charge, fiber orientation, and final mechanical properties were experimentally verified using various techniques. Finally, an alternate approach to design and produce ribbed LFT components is presented. LFT components with ribs can pose processing complexity since the flow of the material is restricted due to the high viscosity of the charge, particularly in narrow channels (rib location). An innovative method of incorporating ribbed features in molded parts is to use pre-consolidated continuous fiber reinforced thermoplastic (CFRT) sections that are co-molded with a skin of LFT. This work focuses on processing and performance evaluation in terms of the static and dynamic properties of LFTs co-molded with pre-consolidated CFRTs, LFTs with ribs, and LFTs without ribs of equal flexural rigidity. Results showed that the LFTs co-molded with CFRTs have higher static and dynamic properties with a progressive failure, as opposed to a brittle failure with lower static and dynamic properties exhibited by both the LFT with and without ribs.

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Engineering Commons



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