Calculation of small-sized cylindrical coil springs on fatigue strength in probabilistic formulation

Abstract

The efficiency of many machines is limited by the resource of cylindrical coil springs, which depends on their strength reliability and stability of power characteristics. Strength calculations of springs are regulated and, as a rule, are limited to traditional testing by the margin factor of fatigue strength. Since springs are related to parts that have random loading and strength characteristics, the expediency of testing springs for reliability and longevity is obvious. The additional requirement for the provision of limited, but sufficient, strength margin with respect to small-sized springs also contributes to the calculations in a probabilistic formulation. The purpose of the work is to develop a methodology for the universal calculation of small-sized cylindrical helical springs for reliability and durability by the criterion of fatigue strength based on the generalization of materials of regulatory guidance documents, empirical and analytical information. An algorithm for determining the statistical parameters of spring fatigue resistance by tangential stresses in the absence or limited base of initial data is presented. The choice of coefficients for the transition from the material fatigue limit to the corresponding spring parameter is justified, taking into account the estimate of its variations. The problems of schematization and statistical processing of loading spectrum of a stepwise and continuous type to calculate the characteristics of the loading of springs are considered. Selection of the coefficient of variation of the load with reference to the springs is substantiated. Statistical characteristics of the loads and fatigue resistance of the springs were used to estimate their probability of failsafe operation and longevity in the probabilistic aspect. An example is given of the fatigue strength calculation in a probabilistic formulation of a cylindrical helical spring for stretching and compressing position 366, taking into account the requirement of minimizing sizes.