Low Cycle Fatigue Evaluation of Duplex Stainless Steel with Material Degradation Effect Under Torsional Load

Abstract

Monotonic torsional and pure torsional low cycle fatigue (LCF) tests with artificial degradation were performed on duplex stainless steel (CF8M). CF8M is used in pipes and valves in a nuclear reactor coolant system. It was aged at 430°C for 3600 hrs. Through the monotonic and LCF tests, it is found that mechanical properties (i.e., yield strength, strain hardening exponent, strength coefficient etc.) are increased and fatigue life (Nf) is decreased with degradation of material. The relationship between shear strain amplitude (γa) and Nf was proposed.

A Study on the Alternative Technology Using Unsm Instead of the Presetting Method for Torsion Bar

“…The hardness test, surface roughness test, and structure observation were carried out in order to obtain variations of mechanical properties regarding of DIN17221 and SCM440 "before and after the treatment". Also, the torsion fatigue test [4][5][6] was executed in order to determine the effects of UNSM treatment on the torsion fatigue characteristics of each material. In order to understand variations of the surface characteristic "before and after the treatment", hardness was measured every 1mm from the surface to the center of a specimen in the circumference direction.…”

Proposal of New Biaxial Fatigue Life Prediction Parameter by Using the Effective Shear Stress for CF8M Stainless Steels

“…The study was performed on virgin material (as received) and degraded material produced by a thermal aging for 3600hours at 430℃ to evaluate the effect of the degradation on the biaxial fatigue life. The profile of the used specimen is a thin walled tubular specimen whose parallel length is 30mm, diameter is 12.5mm and thickness is 1.25mm [5,6,7].…”

“…A biaxial fatigue life prediction was performed for a combined axial-torsional loading using the parameters of Fatemi-Socie (FS) [1] and Smith-Watson-Topper (SWT) [2,3] which is one of the critical plane approaches, and the von Mises equivalent strain [4] before this study [5,6]. As a result, the life prediction by the FS parameter agrees well with the experimental results, while the prediction by the SWT parameter showed the highest error.…”

Multiaxial Fatigue Life Prediction of Duplex Stainless Steels with Thermal Aging at 430°C under Axial-Torsional Load

“…In this study, an experiment was made to obtain the material properties prior to the multiaxial fatigue test [9,10]. Table 2 shows the results of this experiment.…”

“…Table 1 shows the chemical composition of the CF8M used in this study. The study was performed on the virgin material and the degraded material produced by the thermal aging for 3600 hours at 430℃ to evaluate the effect of degradation to the axial-torsional fatigue life [8,9,10].The profile of the used specimen was a thin walled tubular specimen as shown in Fig. 1.…”