FATIGUE LIFE PREDICTION OF ASSEMBLIES OF ROTATING PARTS

In this paper a method is proposed for calculating the reliability of an assembly of rotating parts subjected to fatigue failure. The fatigue life distribution of each individual component in the assembly is considered to be Weibull distributed, with a specific relationship between mean life N-i and applied stress S: i.e. the relationship N(i)S(m)i = C(i)(m)i is valid for the ith component. It is shown how the reliability of the entire assembly can be estimated for both identical and non-identical components. Formulae are developed to express the relationship between scatter in the life of components and scatter in the life of the assembly, and the relationship for mean time to failure (MTTF) of the individual components and the mean time between failures (MTBF) of the assembly. A comparison between replacement policies is also made, when an individual component is replaced upon failure, and when the entire assembly (or a subassembly) is replaced upon failure.