Development of strain monitoring techniques for power plant component lifetime assessment

Abstract

This body of research is comprised of two main threads: determining the material properties of materials integral to the future of the power generation industry, and developing di erent techniques to measure creep strain for use within the laboratory as well as in an industrial setting. The research focusses primarily on the materials austenitic stainless steel 316H and nickel superalloy Inconel 617, although some experiments on ferritic steels have also been performed. Tests were performed to characterise the behaviour of Inconel Alloy 617 at 700 C, and tensile and creep properties have been determined and used in analyses. The validity and accuracy of a novel Alternating Current Potential Drop (ACPD) sensor has been evaluated for di erent materials. It has been shown to be able to detect the strain to within 1 x 10-3 of more widely used strain measurement techniques. Furthermore, it has shown promise in detecting tertiary creep initiation in advance of other methods, even under multiaxial stress states. The application of Digital Image Correlation (DIC) at elevated temperatures has been demonstrated to measure creep strain, and used to visualise the strain eld caused to elicit a better understanding of how a multiaxial stress state a ects deformation on a local level. Results for notched specimens of 316H have been compared to nite element (FE) simulations of creep using the Cocks-Ashby void growth model, with suggestions made to improve the existing model by making considerations for plastic damage.