Session: CS-08-01 ASME Code Section XI Activities-1

Paper Number: 122614

122614 - Fatigue Crack Growth Rates of Austenitic Stainless Steels in Air Under Negative Stress Ratio R for Asme Code Section Xi 

Fatigue crack growth rates da/dN for stainless steels in air environment are provided by the ASME Code Section XI. The fatigue crack growth rates are given by da/dN = C_F(ΔK)ⁿ, where C_F is the fatigue crack growth rate coefficient, n is the fatigue crack growth rate exponent and ΔK is the stress intensity factor range. The coefficient C_F consists of a temperature parameter, S_T, and a scaling parameter, S_R, which is a function of the stress ratio, R. When the stress ratio R is positive from 0 to 1, the parameter S_R increases with increasing the ratio R, and da/dN increases with increasing stress ratio R. When R is less than 0, the parameter is given by S_R = 1.0. Accordingly, fatigue crack growth rates under negative stress ratio are always constant, independent of stress ratios. This means that a cyclic stress state with a minimum that is compressive is considered to cause the same degree of crack growth as one with the same range but a zero minimum. However, from the results of literature survey, experimental data reveal that the fatigue crack growth rates decrease with decreasing R ratios below zero, i.e. negative stress ratios. The objective of this paper is to assess fatigue crack growth rates under such negative stress ratios. An equation for calculating the parameter S_R for stainless steels in air environment is proposed for negative R ratios for the ASME Code Section XI, Appendix Y, based on the literature experimental data surveyed in this study.

Presenting Author: Martin Negyesi Centre for Advanced and Innovative Technologies – VŠB-Technical University of Ostrava

Presenting Author Biography: University studies finished in 2014, awarded by PhD title. During studies 6 months traineeship in Joint Research Center in Petten (Netherlands). Working as junior researcher in UJP Praha a.s. (Czechia) till 2015 and 5 years in Japan Atomic Energy Agency (Japan) till 2020. The main research topic was nuclear fuel safety. From 2020 researcher in Centre for Advanced and Innovative Technologies at VSB-TUO (Ostrava, Czechia). The main research topic is structural integrity assessment.

Authors:

Martin Negyesi Centre for Advanced and Innovative Technologies – VŠB-Technical University of Ostrava
Yoshihito Yamaguchi Japan Atomic Energy Agency
Kunio Hasegawa Japan Atomic Energy Agency
Valery Lacroix Tractebel Engie
Andrew Morley Rolls-Royce plc