Semester

Spring

Date of Graduation

2007

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Jacky C. Prucz

Committee Co-Chair

Hota V. S. GangaRao

Abstract

The orientation of reinforcements in a composite system has major influence on both the elastic and inelastic properties, including failure modes. Manufacturing a polymer composite structural member can be simplified by using certain types of fiber/fabric architecture. The structural performance of a finished composite part does vary with the manufacturing process and constituent materials including fiber and resin type, fiber architecture and Fiber Volume Fraction (FVF).;In this research, the structural behavior of pultruded composite plates having different fiber architecture (uni-, bi-, tri and quadri-) manufactured by the pultrusion process is investigated. Further the mechanical properties of pultruded composites are compared with performance of composites made from compression mold. The strain energy density values of composites manufactured through compression molding and pultrusion are compared with each other so as to create a database to predict the strength and stiffness of composites. In addition, the response of pultruded composites with two different resin systems namely polyurethane and vinyl ester having same fiber architecture are evaluated.;Bi-linear stress-strain response under tension was observed for all composites except for tri-directional composites, which showed tri-linear stress-strain response up to the maximum stress. Under bending, the stress-strain response for uni- and quadri-directional reinforcements are tri-linear, while that for bi- and tri-directional reinforcements, the stress-strain curve has four linear slopes. It is observed that under tension, change in first slope took place at 29% ∼ 40% for composites with various fiber architectures (uni-, bi-, tri- and quadri-directional). In bending, it was observed that for composites with uni-directional fabrics, the change of first slope takes place at about 50% of maximum stress, in case of bi-directional the change of first slope is at 22%, and for all other fabrics i.e., tri- and quadri-directional fabrics, the change of first slope is at about 31%--34%.;The maximum tensile stress and strain in pultruded composites were mostly driven by the fiber orientation, while the maximum bending stress and strain were controlled by interface bonding of resin, fiber architecture and the process type. The ratio of bending strength to tensile strength in pultruded composites varies anywhere from 1.09 to 2.62. For a given fiber architecture, the tensile stress for compression molded plates is always higher than pultruded plates while the bending stress in pultruded composite plates is always higher than the values from compression molded plates. These anomalies are attributed to types of failure modes. With regards to resin system in pultruded composites, vinyl ester resin had more ductility and toughness compared to polyurethane resin, which is contrary to research finding of some researchers. It is likely that the vinyl ester resin is toughened or urethane modified.;The strain energy density of pultruded composites under tension is found to be the lowest value in quadri-directional fabrics compared to other fiber/fabric architecture because of the presence of off-axis plies. The off-axis plies reduce the capability of straining without failure due to stress concentration which in turn reduces the strain energy density. In bending, the strain energy density which is normalized with reference to FVF in the bending direction is within 20% difference regardless of fiber/fabric architecture.

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