Characterization of Fatigue Crack Growth in Austenitic Stainless-Steel Alloy 709 at Elevated Temperatures using a Strip-Yield Model

This study presents a comparison between computational simulations and experimental tests of fatigue crack growth (FCG) in austenitic stainless-steel Fe-25Ni-20Cr (Alloy 709) at 550 degrees C, 600 degrees C, and 700 degrees C. FCG tests were conducted in compact, C(T), specimens at load ratios of R = 0.1, R = 0.5, and R = 0.7. Crack growth rates were measured using several monitoring techniques. In parallel with the experimental tests, a strip-yield model for creep-fatigue crack growth (SYM-CFCG) was employed to simulate crack growth under fatigue loading. The SYM-CFCG software predicts the development of plasticity-induced crack closure (PICC) near the tip of a growing crack. Computation of the PICC allows for predictions of crack growth rate at different R ratios. The evolution of crack-tip opening loads is presented for the entire crack growth history. Predictions of crack length evolution as a function of applied load cycles are compared with the experimental results. In addition, predictions of crack growth rates per cycle versus applied stress intensity factor range are also compared with the experimental measurements. In both cases, excellent agreements between experimental data and SYM-CFCG predictions are obtained. The crack growth data presented can represent a guiding criterion in establishing the fatigue service life of engineering components made of Alloy 709.