A GURSON MODEL IN ASSOCIATION WITH A COHESIVE ZONE MODEL ON THE INVESTIGATION OF CLEAVAGE-DUCTILE TRANSITION IN METALS

Abstract

THE RUPTURE IN METALS CAN OCCUR BY CLEAVAGE, WHERE ALL PROCESS IS CONTROLLED BY STRESSES, OR BY DUCTILE FRACTURE, WHICH TAKES INTO ACCOUNT THE DAMAGE CAUSED BY NUCLEATION AND GROWTH OF VOIDS. THE PROCESS IS THEN DEPENDENT ON STRESSES AND STRAINS. THE LINEAR ELASTIC FRACTURE MECHANICS, WIDELY USED IN ENGINEERING PRACTICE, IS BASED ON THE ASSUMPTION THAT THE FIRST PROCESS PREVAILS, WHICH OCCURS ONLY UNDER CERTAIN CONDITIONS. CONSIDERATION OF THE SECOND FRACTURE PROCESS IS NOT SO WELL DISSEMINATED. IN THIS WORK, TWO METHODOLOGIES ARE CONSIDERED TO TAKE INTO ACCOUNT THE CLEAVAGE-DUCTILE TRANSITION. ONE IS BASED ON THE TVERGAARD-HUTCHINSON'S COHESIVE MODEL AND THE OTHER IS BASED ON THE GURSON- TVERGAARD-NEEDLEMAN'S DUCTILE DAMAGE MODEL. THE TWO METHODOLOGIES ARE CONSIDERABLY DIFFERENT, AND IN THIS WORK, INITIALLY, THE RELATIONSHIPS BETWEEN THE TWO MODELS ARE ESTABLISHED. THEN, THE CONDITIONS FOR A TRANSITION FROM CLEAVAGE TO DUCTILE FRACTURE ARE DETERMINED AND DISCUSSED. MOST OF THE RESULTS ARE PRESENTED BASED ON CRACK GROWTH RESISTENCE CURVES OBTAINED FOR DIFFERENT MATERIAL PARAMETERS. A STRIP IN MODE I RUPTURE IS CONSIDERED FIRSTLY. IT IS SHOWN THAT, DEPENDING ON THE YIELD STRESS AND OTHER FACTORS, THE TWO FRACTURE MODES CAN COEXIST. ALSO, EVEN WHEN ONLY CLEAVAGE IS OCCURRING, IT IS AFFECTED BY INTERACTIONS WITH VOIDS. LASTLY, THE PRESENT SIMULATIONS ARE COMPARED WITH COMPACT TENSION EXPERIMENTAL RESULTS. RESULTS CONSIDERING THE COUPLING BETWEEN THE TWO FRACTURE MODELS PRESENTED A BETTER FITTING WITH EXPERIMENTS THAN OTHER SIMULATIONS WHERE THE COUPLING IS NOT CONSIDERED.