Ageing and Fatigue Life of Structural TLP Flexelements

Abstract

This paper presents a methodology for estimating the fatigue life of elastomerlsteel flexelements that includes the effects of both mechanical fatigue loads and ageing of the elastomer. Previous methods calculated the rate of fatigue crack growth in the elastomer layers of flexelements using fracture mechanic analysis and a material fatigue model obtained from tests on new were taken into account, the calculated fatigue life ranges from 160 years to 400 years depending on the conservatism of the assumptions used. The effect of ageing is obviously significant. The analysis uses data generated from elastomer samples exposed to accelerated ageing conditions. A special purpose fracture mechanics program calculates the crack growth in each layer for each load in the yearly fatigue spectrum. The material properties are updated and total crack length is computed on a year-by-year basis until the failure criteria is reached.The present approach may remove some of the uncertainty associated with structural elastomer design, result in more realistic estimates of elastomer fatigue life, and may lead to the use of safety factors commonly associated with the design of more familiar structures.