ANALYSIS ON RIGIDITY OF COMPOSITE HELICAL SPRING AND ITS INFLUENCE FACTORS

A new type of composite cylinder helical spring is prepared in this study. The cross section of spring wire is annular. The spring wire is made from fiber composite plies and the fiber composite plies are alternately laid out along the directions of ±45° from the axis of spring wire. At the same time,a series of quasi-static compression tests are carried out on the composite spring specimens. The shear modulus in the stiffness expression of isotropic helical spring will be equivalently replaced by the shear modulus of the fiber composite plies with ±45° directions. Hence, the stiffness expression of the new type of composite spring can be obtained. Based on the stiffness expression, a variety of influence factors and their degree of influence on the rigidity of the new type of spring will be analyzed. The studied results show that the stiffness coefficient of composite spring obviously increases with the increase of the Young’s modulus of fiber, the volume fraction of fiber, and the outer diameter of spring wire, and vice versa. The Young’s modulus of matrix and the Poisson’s ratio of composite material have a very small effect on the stiffness of composite spring. The inside diameter of spring wire almost has no effect on the stiffness of composite spring in a certain size range, but beyond the range, the stiffness coefficient significantly decreases with the increase of the inside diameter of spring wire. The stiffness coefficient of composite spring obviously decreases with the increase of the number of active coils and the average diameter of the coil, and vice versa.