The effect of proof loading on the fatigue behaviour of stud link chain

Abstract

Although stud link chain is routinely proof loaded during its manufacture, the effect of residual stresses imposed by this operation on the fatigue strength of the chain has not been quantitatively investigated. This paper discusses the results of constant amplitude fatigue tests on stud link chain segments which have received proof loading at various levels. The chain was heat treated before fatigue testing to relieve manufacturing residual stresses and then proof loaded at various levels from zero to 86% of its break strength. Tests were performed at two mean load levels and three load amplitudes. Failure site trends are reported and correlated with results of a finite element stress analysis. Residual stress estimates are used with standard fatigue damage parameters to estimate the fatigue life of the chain and predictions are compared to the experimental data. Low cycle fatigue parameters were derived from a previous test programme for open link chain. Proof loading was shown to increase substantially the fatigue life of the stud link chain. Residual stresses can explain the increase in fatigue life. Neuber's rule demonstrated the ability to model the data trends.