Strength characterization of chopped-fiber composites using Iosipescu test method
In the aviation industry, composites are considered high-performance structural materials. Composite materials are mainly used in fuselages, wings, propellers, interior components, landing gears, doors, etc. Their main advantages are high strength and stiffness, and low density, in comparison to heavy weight materials such as metals, thereby producing a low weight in the finished part. The major drawback with composite materials is their inability to meet complex design requirements, hence the reason for investigating discontinuous-fiber composites. These composites have relatively low strength and stiffness, but can be easily formed into complex shapes and sizes, thus meeting the design requirements of many industries. The strength properties of discontinuous-fiber composites can reach that of continuous-fiber composites if their aspect ratios are high and their fibers are aligned, but in actual practice it is difficult to maintain good alignment with discontinuous fibers. Nevertheless, discontinuous-fiber composites are typically more affordable than continuous-fiber composites. The main objective of this research was to analyze this problem by characterizing the shear strength properties of discontinuous-fiber composites that have a suitable alignment in order to satisfy the industrial needs for developing effective products with high efficiency and low cost. In this thesis, the in-plane shear strength properties of quasi-isotropic discontinuous composites were calculated using the Iosipescu shear test method. The experimental results were analyzed using digital image correlation (DIC) analysis to determine the strain field in the region of interest (ROI), which provides the shear strain of the specimen. Thus, shear stress vs shear strain plots were mapped, and from these plots, shear stress, stiffness, and modulus were determined and characterized. The theoretical results of failure thus obtained were compared with the experimental results.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering