Laboratory apparatus for in-situ corrosion fatigue testing and characterisation of fatigue cracks using X-ray micro-computed tomography

This paper presents the design, construction and assembly of laboratory apparatus to undertake in-situ corrosion fatigue tests in a sour corrosive environment under uniaxial fatigue loading. The bespoke test cell allows periodic non-destructive X-ray micro-computed tomography of the specimen in-situ during fatigue testing and thus enables monitoring of material degradation as it progresses and in particular the pit-to-crack transition. This approach provides more direct information on crack initiation than complementary ex-situ techniques such as Scanning Electron Microscopy (SEM) of post-test metallographic specimens. Moreover, the apparatus was designed to allow a fatigue cycle to be interrupted and maintain the sample under static tensile load, during X-ray tomography scans. This process reduced the risk of premature crack closure during interrupted tests. Results presented herein demonstrate the performance and reliability of our approach and will hopefully stimulate other groups to employ similar ‘lab-scale’ initiatives.