고온에서 Alloy 800H의 저사이클 피로 특성에 대한 통계적 변동성에 관한 연구

Abstract

Alloy 800H, an austentic Fe-Ni-Cr alloy with higher Ni and Cr contents than conventional stainless steels, is one of the candidate materials for key structural components such as control rod systems, hot gas duct, core barrels, core supports, and a shut-down cooling systems for the very high temperature reactor (VHTR) systems. The start-up and shut-down, and power transmission of the reactors cause low cycle fatigue (LCF) and creep-fatigue (C-F). The research results of many scholars have been published in the literature on the characterization of low cycle fatigue and creep-fatigue properties of Alloy 800H. However, most of their research works are the deterministic study about the low cycle fatigue properties. It is well known that a significant scatter of the cyclic stress-strain responses was observed for a nuclear reactor material, steel pipe weld metal. The statistical nature of the data for low cycle fatigue properties of Alloy 800H has not investigated in the past studies. Therefore, it is valuable to investigate the statistical variability of the low cycle fatigue properties of Alloy 800H at high temperature. The purpose of this study is to investigate the statistical variability of low cycle fatigue properties of Alloy 800H at a high temperature of 850℃. Specially, the variability associated with the low cycle fatigue properties in a mid-life hysteresis loops for data and fatigue life are examined. In this study, the strain-controlled constant amplitude low cycle fatigue tests at a high temperature of 850℃ were performed on six identical specimens of Alloy 800H in accordance with ASTM standards E606 at a strain rate of . All the low cycle fatigue tests are performed at constant total strain range value of 0.6% with a cyclic strain ratio of -1. In this test conditions, the cyclic stress-response behavior showed cyclic softening phenomenon. The stress amplitude at the mid-life follows 2-parameter Weibull distribution. The shape parameter was estimated the value of 36. The plastic strain amplitude also follows 2-parameter Weibull distribution. And, the shape parameter was estimated the value of 70. Namely, the statistical variabilities for the stress amplitude and plastic strain amplitude at the mid-life in Alloy 800H at a high temperature of 850℃ were known a little. However, the fatigue life have a larger scatter than those of the stress amplitude and plastic strain amplitude. The fatigue life also follows well 2-parameter Weibull distribution. And, the shape parameter was estimated the value of 8.7. Consequently, although the stress amplitude and plastic strain amplitude have a variability, the repeatability have excellent. However, the fatigue life have a significant scatter with the coefficient of variation 0f 14%.