Determination of shear modulus in bamboo fibers composite in torsion tests

Natural Fibers, when employed as reinforced in composites, contribute to the reduction of environmental impacts, moreover, its use decreases costs and reduces the weight of components. Several studies are carried out for the application of these materials in the automobile industry. Some mechanical behaviors such as elasticity moduli have already been experienced in these types of composites. However, for the use of these materials in quality and safety products, more mechanical information is required. The purpose of this study is to determine the shear moduli G(13 )nd G(23) of composites with vegetable fibers. Torsion tests were performed on epoxy resin composites with bamboo fibers without chemical treatment: one with 280-mm unidirectional long fibers and another one with 25-mm discontinuous short fibers. The torsion test was based on the variation of the base/ height ratio (b/h) of the test specimen and at each base reduction a new torsion test was carried out. All tests featured a linear relationship between the torsional angle and the torque. On the experimental points plotted, the Saint-Venant equation modified to orthotropic material was interpolated, thus allowing the determination of the shear modulus G(13 )and G(23) for the two composites. The shear moduli for long fiber composites presented the following values: G(13) = 1.441 GPa, G(23) = 1.726 GPa, and for short fibers G(13) = 1.889 GPa, G(23) = 1.290 GPa. The results showed that the composites are orthotropic for shear modulus due to the compression molding process.