A thermoplastic matrix continuous fiber reinforced composite impregnation method by direct polymer extrusion
Date
2018
Authors
Hedin, Kevin M., author
Radford, Donald W., advisor
Ma, Kaka, committee member
Heyliger, Paul, committee member
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Abstract
During component design, continuous fiber reinforced composite material systems are often chosen largely based on their structural efficiency. Their mechanical properties, such as specific strength and specific stiffness, are often cited as significant advantages over the use of other materials. However, composite component production often lacks the capability to provide the local variation necessary to ensure that 1) the reinforcing fibers are best aligned with anticipated loads, and 2) the ideal matrix composition and fiber volume fraction are found throughout the composite part. In practice, these limitations result in composite components that do not demonstrate the maximum possible efficiencies inherent to the fiber-reinforced composite material system. To further increase the flexibility of polymer matrix continuous fiber reinforced composites manufacturing methods, a new thermoplastic impregnation method was developed. This proposed method adds a thermoplastic matrix, which has previously been proven to allow significant variation of local fiber orientation, to the reinforcing fiber just prior to the consolidation of the composite. The increased independence of matrix and fiber addition should allow the local variation of volume and composition of the added matrix, while using less and simpler hardware than previous, similar efforts. In this work, the quality of material deposited from the proposed process is evaluated. The maximum possible quality of the proposed method and also that of a similar process that uses a commercially available material system were determined, primarily using short beam shear (SBS) testing. The material system of both methods consisted of E-glass continuous fiber reinforcement with a PETG matrix. It was found that both manufacturing processes are capable of producing samples with an SBS strength of approximately 53 MPa, and it was concluded that the proposed process has the capability to deposit material of comparable quality to that produced by the baseline method. Subsequent thermal analysis, fiber volume fraction/void content measurement, and metallographic imaging were conducted to investigate the effects of using two different PETG compositions on the SBS strength of composite material produced by the proposed process. It was found that, while using the proposed process, the PETG matrix with a lower glass transition temperature allowed better consolidation of the resulting composite part, ultimately increasing SBS strength. Each process parameter used in the proposed process was evaluated for the practical significance of its effects on SBS strength, which facilitated 1) an understanding of the underlying mechanisms of the process, and 2) a tenable simplification of the process that should reduce operating costs and also demonstrates its robustness via insensitivity to many of the possible process variations. Finally, it was established that the material inputs to the proposed process are relatively inexpensive: Using PETG and continuous E-glass fiber in the proposed process reduces material input cost by at least 52% compared to using commingled PETG and E-glass fibers in the baseline process, on a $/kg basis.
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Subject
fiber
manufacturing
thermoplastic
infusion
composite
optimization