Plasticity and Fracture Behaviors of Marine Structural Steel, Part V: Effects of Strain Rate and Temperature

doi:2011.25.3.73

J. Ocean Eng. Technol. > Volume 25(3); 2011 > Article

J. Ocean Eng. Technol. 2011;25(3):73-84.
DOI: https://doi.org/10.5574/KSOE.2011.25.3.073

Choung Joon-Mo,Im Sung-Woo,Kim Kyung-Su

Dep't of Naval Architecture and Ocean Engineering INHA University,Steel Structure Research Lab. RIST,Dep't of Naval Architecture and Ocean Engineering INHA University

조선 해양 구조물용 강재의 소성 및 파단 특성 V: 온도 의존성을 고려한 변형률 속도에 관한 실험적 연구

정준모,임성우,김경수

인하대학교 조선해양공학과,포항산업과학연구원 강구조연구소,인하대학교 조선해양공학과

Keywords: Strain rate, Dynamic hardening factor(DHF), Cowper-Symonds constitutive equation, Dynamic strain aging, plastic strain

핵심용어: 변형률 속도, 동적 경화 계수, 코퍼-시몬드 구성방정식, 동적 변형률 시효, 소성 변형률

Abstract

This is the fifth in a series of companion papers dealing with the dynamic hardening properties of various marine structural steels at intermediate strain rates. Five steps of strain rate levels (0.001, 1, 10, 100, 200/s) and three steps of temperature levels (LT ($-40^{circ}C$), RT, and HT ($200^{circ}C$)) were taken into account for the dynamic tensile tests of three types of marine structural steels: API 2W50 and Classifications EH36 and DH36. The total number of specimens was 180 pieces. It was seen that the effects of dynamic hardening became clearer at LT than at RT. Dynamic strain aging accompanying serrated flow stress curves was also observed from high temperature tests for all kinds of steels. The dynamic hardening factors (DHFs) at the two temperature levels of LT and RT were derived at the three plastic strain levels of 0.05, 0.10, 0.15 from dynamic tensile tests. Meanwhile, no DHFs were found for the high temperature tests because a slight negative strain rate dependency due to dynamic strain aging had occurred. A new formulation to determine material constant D in a Cowper-Symonds constitutive equation is provided as a function of the plastic strain rate, as well as the plastic strain level. The proposed formula is verified by comparing with test flow stress curves, not only at intermediate strain rate ranges but also at high strain rate ranges.