Multiaxial notch fatigue of corroded cast iron pipes

Abstract

Grey Cast Iron (GCI) water pipes often develop localised corrosion pits that act as notches and can also experience biaxial fatigue stresses, resulting in a multiaxial notch fatigue problem. This paper experimentally investigates for the first time, the high-cycle fatigue sensitivity of GCI to localised notches, under bending and biaxal loading, and validates a multiaxial notch fatigue model for GCI. The work uses a recently developed, novel biaxial fatigue experiment to generate the first fatigue data for GCI featuring pit-like notches. Approximately 40 new fatigue tests were completed to calibrate and test four multiaxial notch fatigue models, and to investigate the effects of notch root radius, localised notches, bending loading, and biaxial loading. The data shows that pit-like notches can have a statistically significant influence on the fatigue strength of GCI when $K_{t,n}>4$. Additionally, 180° out-of-phase biaxial loading was found to reduce the fatigue strength of un-notched specimens by 28 %. The Effective Volume notch fatigue model, coupled with the linear-elastic Smith-Watson-Topper criterion, was found to give good predictions for notched GCI pipes subject to uniaxial and bending loading. This work highlights the ability of the Effective Volume approach to make good fatigue life estimates for thin, notched components featuring inclusions, where critical distance-based approaches performed less well. Future work on similar problems may wish to consider this approach.