STUDY ON FRICTIONAL EFFECTS ON MECHANICAL PROPERTIES OF COMBINED DISC SPRINGS

To study the effects of friction on the mechanical properties of combined disc springs, an incremental energy method was employed to investigate the mechanisms of three friction factors in a typical combination disc spring device, in which the frictions are from spring end plate, from spring conical surface, and from spring guide tube. The effects of different friction factors on the increase and decrease in spring force during the loading and unloading stages were quantitatively studied. An indicator for evaluating the effective self-centering ratio of spring was proposed upon the frictional effects. Numerical simulations were conducted to parametrically analyze the mechanical properties of combined disc springs with different spring series. The simulation results revealed the influence of friction factors on the spring performance and the effective self-centering ratio. Moreover, the accuracy of the theoretical prediction method was verified upon the experimental results of combined disc springs. The results indicate that the loading path is inconsistent with the unloading path due to frictions, presenting an obvious unsymmetric characteristic at the load-displacement curve. The number of springs in parallel has a significant influence on the conical surface friction but has a secondary influence on the end plate friction. The friction between the spring and guide tube should be avoided because it is detrimental to the normal functional state of the disc spring. However, the existence of the gap between the spring and the tube is able to reduce the unexpected friction between them. The level of effective self-centering ratio is correlative to the type of spring, of the number of stacked springs, and of the magnitude of friction coefficients, which should be considered comprehensively in design.