조선 해양 구조물용 강재 파단의 이론적 배경

초록

Main pillars of this paper are to provide theoretical backgrounds of fracture phenomena in marine structural steels. In this paper, various fracture criteria are theoretically investigated: shear failure criteria with constant failure strain and stress triaxiality-dependent failure strain (piecewise failure and Johnson-Cook criteria), forming limit curve failure criterion, micromechanical porosity failure criterion, and continuum damage mechanics failure criterion. It is obvious that stress triaxiality is a very important index to determine failure phenomenon for ductile materials. Assuming an piecewise failure strain curve as a function of stress triaxiality, the numerical results are well coincided with test results for smooth and notched specimens where low and high stress triaxialities are observed. Therefore it is proved that a failure criterion with reliable material constants presents plastic deformation process as well as fracture initiation and evolution.