조선 해양 구조물용 강재의 파단 변형률

초록

This is the third of several companion papers dealing with derivation of material constants for ductile failure criterion under hydrostatic stress. It is observed that ultimate engineering stresses and elongations at fracture from tensile tests for round specimens with various notch radii tend to increase and decrease, respectively, due to stress triaxiality. The engineering stress curves from tests are compared with numerical simulation results, and it is proved that curves from two approaches are very closely coincide each other. Failure strains are obtained from equivalent plastic strain histories from numerical simulations at the time when the experimental engineering stress falls down suddenly. After introducing a new concept of average stress triaxiality and accumulated average strain energy, material constants of Johnson-Cook failure criterion for critical energies of 100%, 50%, and 15% are presented. Experimental results conducted for EH-36 steel are relatively good agreement with 100% critical energy whereas literature states that aluminum fits with 15% critical energy. Therefore it is expected that a unified failure criterion, available for most kinds of ductile materials, of critical energy according to the used materials can be provided.