Theoretical and practical approaches for novel composite evolute springs

Abstract

A combined experimental/analytical approach for an efficient evaluation of stiffness and characteristic curves of fiber reinforced plastic volute springs is presented in this work. Before performing the analysis mentioned in previous lines, in the early chapters, it can find the most common types of fibers, resins (matrices) and manufacturing processes used to produce composite laminates been briefly described. It also describes the analytical approaches that currently exist to determine the elastic constants of composites such as the longitudinal and transversal modulus, Poisson’s ratios and shear moduli; it also describes the improved and semi-empirical formulas to calculate the effective shear moduli and the transversal modulus. At the end of the chapter, some manufacturing methods of fiber reinforced plastic springs are described. Since fiber reinforced plastic volute springs are novel products, the fourth chapter presents and describes basic considerations that it must be taken into account when selecting material (fibers, resins, and additives) to manufacture these springs. At the end of the chapter, a method to produce volute springs is presented. The fifth chapter presents the elastic constant calculations for laminates used to manufacture volute springs. An experimental/analytical method has also been performed to determine in-plane and out-of-plane shear moduli since these material constants are of greater importance in the rate spring calculation hence any crosssection of these springs shows the major load being torsional. On the one hand the analytical method to calculate these shear moduli is based on Sumsion’s guidelines that use the theory developed by Lekhnitskii for anisotropic materials; on the other hand, it has been done torsion test of rectangular bars, which were manufactured using vacuum infusion method, to obtain shear moduli experimentally. Finally, calculated values of shear moduli are used to determine stiffness and characteristic curves of volute springs in an analytical and experimental method. It is proposed to use the in-plane shear modulus in the classical calculation method for steel volute springs and to compare results obtained with compression test results carried out on fiber reinforced plastic volute springs. Consistent results are achieved by performing this combined analytical and experimental method concluding that the best behavior of fiber reinforced plastic volute springs is when fibers have an orientation of +/ 45° concerning the main axis of the laminate.