조선 해양 구조물용 강재 변형률 경화 및 변형률 속도 경화의 이론적 배경

초록

In this paper, global study trends of material behaviors are investigated regarding static and dynamic hardenings and final fractures of marine structural steels. Especially, after reviewing all papers published in the 4th and 5th ICCGS (International Conference on Collision and Grounding of Ship), the used hardening and fracture properties are summarized explicitly presenting material properties. Although some papers have tried to employ new plasticity and fracture models, it is obvious that most papers still employed ideal hardening rule such as perfect plastic or linear hardening and simple shear fracture criterion with assumed value of failure strain. HSE (2001) presented pioneering study results regarding temperature dependency of material strain hardening at the various level of temperatures, but did not show strain rate hardening at intermediate or hight strain rate ranges. Nemat-Nasser and Guo (2003) carried out fully coupled tests for DH-36 steel: strain hardening, strain rate hardening, and temperature hardening and softening at multiple steps of strain rates and temperatures. Main pillars of this paper are to provide theoretical backgrounds of strain and strain rate hardening. In addition, the procedure and methodology to derive material constants for static hardening constitutive equations of Ludwik, Hollomon, Swift, and Ramberg-Osgood and for dynamic hardening constitutive equations of power, Cowper-Symonds and Johnson-Cook.