Date of Award

2004

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Forest Resources

Advisor

Barry Goodell

Second Committee Member

Roberto A. Lopez-Anido

Third Committee Member

Douglas Gardner

Abstract

The Composite Pressure Resin Infusion System (ComPRIS) is a newly developed process whereby resin is infused through fiber reinforcement via external pressure to produce Fiber Reinforced Polymer (FRP) composite material. The process can be modified so that the fiber reinforcement can be bonded to other substrate or core materials to develop hybrid composite products. The various forms of the substrates can be laminated or consolidated at the same time that the FRP composite is fabricated within or on the surface of the core materials. ComPRIS offers several advantages over other resin infusion processes, e.g. Vacuum Assisted Resin Transfer Molding (VARTM). The use of pressure allows for a greater driving force of resin into fiber reinforcement and/or porous material than is possible using a vacuum. As a result, the penetration of heavy towed fabrics and thick parts, without the need for flow or resin distribution media, is achieved. In addition, ComPRIS-fabricated laminated products exhibit a graded interfacial boundary, or resin interplzase, between bonded materials. This resin interphase may result in a stronger bond between laminates and may be less prone to delamination than conventional produced adhesive bond interfaces. An additional advantage of the ComPRIS process, and the focus of the work presented here, is the virtual elimation of vacuum-induced voids in the finished FRP material. Previous studies have repeatedly shown that an increased void content adversely affects certain mechanical properties, specifically matrix-dominated properties, of FRP composites. Although Vacuum Assisted Resin Transfer Molding (VARTM) fabricated parts generally have significantly smaller void contents than parts made through hand lay-up processes, vacuum-induced voids and/or defects may still prohibit the FRP material from performing at optimum levels. In the first part of this work, image analysis using an electron microprobe in backscatter mode is introduced as a method to provide a qualitative comparison of void content and fiber packing in FRP materials. Composite parts were fabricated using the VARTM and ComPRIS processes. Voids were observed in the composite specimens fabricated by the vacuum-assisted process, whereas no significant voids were observed in the composite specimens fabricated by the ComPRIS process. The apparent difference in void content is attributed to the difference in the resin infusion driving force, i.e., vacuum versus pressure. Backscattered electron imaging (BEI) of samples using an electron microprobe proved to be a suitable technique for imaging fiber reinforced polymer surfaces. The objectives of the second part of this research were to evaluate the spatial correlation of void content and apparent interlaminar shear strength (ILSS) in VARTM- and ComPRIS- fabricated FRP composites, and to assess factors that may impact strength issues. It was again found that materials fabricated by ComPRIS possessed fewer voids and also exhibited a higher ILSS than specimens made using VARTM. Because the pressure above the resin is not lowered during the ComPRIS process, existing voids do not dilate, nor is there a danger of outgassing. Furthermore, depending on the pressure level used in the process, existing bubbles may be collapsed and the molecular gases dispersed in the solution.

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