Date of Award

12-2012

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Advisor

Roberto A. Lopez-Anido

Second Committee Member

Vincent Caccese

Third Committee Member

Senthil Vel

Abstract

The very nature of continuous fiber composite materials, with their heterogeneous structure of layered and interwoven fibers bound together by a polymer resin matrix, lead to an inevitable variability in mechanical properties. This is especially true if the fabrication process is not well controlled. Unlike fabricating components with metals, where the properties of the material are known beforehand, the final properties of the composite material are determined during the process of fabricating the composite part. The research described herein was undertaken to better enable the use of polymer matrix composites in the marine construction industry by developing a knowledge base on the inter-relationships between process parameters and system material properties.

Professionals from the marine composite fabrication industry were consulted to obtain insight into the process parameters of concern for today’s composite materials and manufacturing methods. The survey of industrial marine designers and fabricators was intended to identify potential sources of variability and to characterize processing issues. A set of composite constituent materials, vinyl-ester resin and woven roving fiber reinforcement, and a single processing method, vacuum assisted resin transfer molding (VARTM), were selected for further investigation based on this industry survey. In addition to the survey, a thorough literature review was conducted to identify current research areas for VARTM processing of composite laminates.

A manufacturing round-robin study was conducted amongst marine composite fabricators to establish the extent of material property variability. The methodology employed for the experimental material characterization included the use of three-dimensional digital image correlation (DIC) methods to measure the full-field strain in the test specimens. The DIC method was chosen over conventional foil strain gage techniques since it can better capture, and account for, the large strain gradients that are present in composite specimens fabricated with woven roving fabrics typically found in marine grade composites. The statistical analysis of the test results was performed to characterize the variability in material properties in accordance with the guidelines set forth in Composite Materials Handbook-17, which is the composite industry’s standard for testing and analysis of laminated composite materials. A methodology was developed based on these guidelines and employed throughout the different studies conducted. A laboratory study of resin, fiber and manufacturing effects was designed to capture the relationship between the processing parameters and the final material properties of the composite laminates. The parameters and test methods used in this study were selected based on the results of the industry survey and the round-robin study.

This integrated research will contribute to advance scientific understanding on the interrelationships between process parameters and mechanical property variability of marine composite materials. The broad impact of the research is to enable the development of rational composites fabrication methods and reliable engineering design procedures.

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