Negative-R Fatigue Short Crack Growth Rate Testing on Austenitic Stainless SteelsAdam Griffiths – Jacobs, &nbsp;Peter Gill – Jacobs,&nbsp;Ben Coult – Jacobs, Jack Beswick - Jacobs, Norman Platts – Jacobs, Jonathan Mann – Rolls Royce, Chris Currie - Rolls Royce,&nbsp;Joe Airey – Rolls RoyceAbstract:The effect of environment on fatigue life is currently assessed using methods (e.g. NUREG/CR-6909), which may be excessively conservative when applied to plant components and loading transients.&nbsp; There are many reasons why these methods are thought to be conservative, but the focus of this paper is to provide a more accurate description of crack growth at length-scales that are not usually considered in a crack growth assessment. This progression from initiation to short and long crack growth is being considered to support the development of an improved assessment methodology for environmental fatigue based on a Total Life Prediction approach.&nbsp; This methodology aims to predict fatigue lifetimes that are adequately, but not excessively, conservative. Such an approach requires short crack growth data, which would bridge the gap between fatigue nucleation and long crack growth (Paris Law).&nbsp;Previous negative-R long crack growth testing using corner-crack specimens measured the effects of crack closure under compressive loading, and has been used to address some of the conservatism in existing assessment methods. This methodology has been developed further to enable negative-R short crack growth testing with in-situ monitoring using DCPD. Testing has been undertaken in both high temperature air (300ºC) and a simulated PWR primary water chemistry at 300ºC on both cold-worked and non-cold-worked stainless steel specimens at a load ratio of R = -1. Two heats of stainless steel have been tested, each with a different grain size, in order to investigate the effect of grain size on short crack growth rates. FEA modelling has been undertaken to both correlate DCPD response with crack growth measurements, and determine the effective stress intensity factors applied under the loading conditions based on the specific material properties.&nbsp;This paper will describe the methodology and findings from this negative-R short crack growth test programme. Crack growth rates have been compared to those predicted in ASME, Code Case N-809 and results from material specific in-house testing.&nbsp;&nbsp;

Negative R Fatigue Short Crack Growth Rate Testing on Austenitic Stainless Steels

Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2021/volume/85314

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