Doctoral Dissertations

Orcid ID


Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Mechanical Engineering

Major Professor

Uday K. Vaidya

Committee Members

Chad E. Duty, Amit K. Naskar, Kenneth D. Kihm


Long fiber thermoplastic (LFT) composite materials are increasingly used in high performance lightweight automotive, sporting, and industrial applications. LFT composites are processed with extrusion-compression molding (ECM) and/or injection molding (IM). Melt extrusion offers unique opportunities to align long fibers in a thermoplastic polymer melt. The properties of LFT materials are highly influenced by processing techniques which leads to different porosity content, fiber length distribution, and fiber orientation distribution. Hence, it is important to understand the various LFT processing techniques and their effect on mechanical, thermal, and microscopic properties.

The fundamental process-property relationships in LFT composites are investigated in this dissertation. Additionally, there is a genuine need for efficient and reliable composite manufacturing techniques which can provide reduced weight, superior crashworthiness, improved efficiency, reduced processing complexity and cost-effective structures.

The aim of this work is to explore aligned long fibers and enhance the performance of long fiber composites through innovations in overmolding process. The overmolding approach offers an efficient alternative process to traditional sheet molding compound (SMC), glass mat thermoplastic (GMT), and rib reinforced thermoplastic composites.

In this work, aligned LFT sheets processed via melt extrusion with continuous fiber like properties were considered. Additionally, LFTs are processed utilizing extrusion compression molding (ECM) process, and overmolded with continuous fiber reinforcement to evaluate the structural performance. The melt extruded and overmolded LFT samples were characterized using nondestructive and destructive techniques to evaluate fiber alignment, fiber distribution, manufacturing defects, interfacial bonding, and the effect of continuous reinforcement on LFT composite.

Keywords: Long fiber thermoplastic, Extrusion compression molding, Filament winding Destructive testing, Non-destructive testing, Computational modeling

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