Mechanical Spring Reliability Assessments Based on FEA Generated Fatigue Stresses and Monte Carlo Simulated Stress/Strength Distributions

The reliability assessment of a mechanical spring is required to evaluate different spring designs for various spring deflection applications. For the fatigue failure mode, the spring reliability is predominantly dependent on the service fatigue stress and the fatigue strength of the spring. In reality, significant statistical scatters of both fatigue stress and fatigue strength are often inherent and inevitable. Therefore, the spring reliability assessment for highvolume production is a statistical interference analysis of fatigue stress and fatigue strength. In many engineering cases, neither the fatigue stress nor the statistical interference can be analytically solved; finite element analysis (FEA) and Monte Carlo simulations are thus employed. Finite element analysis is used to generate the fatigue stresses as functions of spring deflections for displacement-controlled boundary conditions. The spring reliabilities as functions of fatigue life are predicted based on the Monte Carlo simulations of spring deflection and spring fatigue strength distributions. The methodology described in this paper is equally good for force-controlled boundary conditions; and can be applied as a general probabilistic approach to evaluate the reliability of many other types of mechanical components. Application of this methodology has the potential for reducing the product developmental cost and improving product robustness.