A Study of Stress Ratio Influence on the Fatigue Crack Growth Characteristics of Pressure Vessel Steel at Low Temperature

J. Ocean Eng. Technol. 2001;15(3):100-106.

압력용기용 강의 응력비에 따른 저온 피로균열 진전특성에 관한 연구

박경동,하경준,박형동

부경대학교 기계공학부,부경대학교 대학원 기계공학부,부경대학교 대학원 기계공학부

Keywords: Fatigue crack propagation, Low temperature, Stress ratio, Cryogenic-brittleness

핵심용어: 피로균열전파, 저온, 응력비, 저온취성

Abstract

In this study, CT specimens were prepared from Pressure Vessel Steel which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{circ}C$, -3$0^{circ}C$, -6$0^{circ}C$, -10$0^{circ}C$ and -12$0^{circ}C$ and in the range of stress ratio of 0.05 and 0.3 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range ${Delta}K_{th}$ in the early stage of fatigue crack growth (Region I) and stress intensity factor range ${Delta}K$ in the stable of fatigue crack growth (Region II) was increased in proportion to descent temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da/dN $-{Delta}K$ in Region II, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It was assumed that the fatigue crack growth rate da/dN in proportion to descending temperature in Region II and the cryogenic-brittleness greatly affect a material with decreasing temperature.