Torsional shear properties, composites

Figure 5. Torsional shear properties of two 3D composites subjected to similar processing.

Apart from the short beam shear test, which measures the interlaminar shear properties, many different specimen geometry and loading configurations are available in the literature for the translaminar or in-plane strength measurements. These include the losipescu shear test, the 45°]5 tensile test, the [10°] off-axis tensile test, the rail-shear tests, the cross-beam sandwich test and the thin-walled tube torsion test. Since the state of shear stress in the test areas of the specimens is seldom pure or uniform in most of these techniques, the results obtained are likely to be inconsistent. In addition to the above shear tests, the transverse tension test is another simple popular method to assess the bond quality of bulk composites. Some of these methods are more widely used than others due to their simplicity in specimen preparation and data reduction methodology. 

In-Plane Shear Properties. The basic lamina in-plane shear stiffness and strength is characterized using a unidirectional hoop-wound (90°) 0.1 -m nominal internal diameter tube that is loaded in torsion. The test method has been standardized under the ASTM D5448 test method for in-plane shear properties of unidirectional fiber-resin composite cylinders. D5448 provides the specimen and hardware geometry necessary to conduct the test. The lamina in-plane shear curve is typically very nonlinear [51]. The test yields the lamina s in-plane shear strength, t12, in-plane shear strain at failure, y12, and in-plane chord shear modulus, G12. 

Polymer composites. The composite research at the Institute is led by Prof. Wu Renjie, Deputy director of the Institute. Chen, et al. (14), studied the effect of oxidation of carbon fiber on the wettability by the binder resin. With the aid of ESCA, they showed that the Q/C ratio on the fiber surface increased with the oxidation time. The interlaminar shear strength also increased correspondingly. Cai Weizhen and her colleagues showed me their exceptional setup for a carbon-fiber composite study. They built their own torsion pendulum for the study of dynamic mechanical properties of the composite and a contact angle goniometer for the study of the composite interface. It was apparent that surface treatment of carbon fiber was their major concern. 

Sawada Y, Shindo A, Torsional properties of carbon-fibers, Carbon, 30(4), 619-629, 1992. Swanson SR, Merrick M, Toombes GR, Comparison of torsion tube and losipescu in-plane shear test results for a carbon fibre reinforced epoxy composite, Composites, 16, 8220, 1985. 

Mechanical properties probably are the most important properties of fibers. Fibers must possess sufficient mechanical properties so they can be converted into useful products, such as textiles, composites, etc. The mechanical properties of fibers also limit the performance potential that can be achieved by these products. There are many different types of mechanical properties, including tensile, torsional, bending, and compressional properties. Among them, tensile properties are the most widely studied for fibers, probably because of their unique shape. However, other types of mechanical properties also are important. This chapter begins with the basic definitions of Hooke s law, stress, strain, and tensile, bulk and shear moduli, followed by a detailed discussion on tensile, torsional, bending, and compressional properties of fibers. 

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