PREDICTION OF PLASTIC INSTABILITY IN SHEET METALS DURING FORMING PROCESSES USING THE LOSS OF ELLIPTICITY APPROACH

Abstract

THE PREDICTION OF PLASTIC INSTABILITY IN SHEET METALS DURING FORMING PROCESSES REPRESENTS NOWADAYS AN AMBITIOUS CHALLENGE. TO REACH THIS GOAL, A NEW NUMERICAL APPROACH, BASED ON THE LOSS OF ELLIPTICITY CRITERION, IS PROPOSED IN THE PRESENT CONTRIBUTION. A POLYCRYSTALLINE MODEL IS IMPLEMENTED AS A USER-MATERIAL SUBROUTINE INTO THE ABAQUS/IMPLICIT FINITE ELEMENT (FE) CODE. THE POLYCRYSTALLINE CONSTITUTIVE MODEL IS ASSIGNED TO EACH INTEGRATION POINT OF THE FE MESH. TO DERIVE THE MECHANICAL BEHAVIOR OF THIS POLYCRYSTALLINE AGGREGATE FROM THE BEHAVIOR OF ITS MICROSCOPIC CONSTITUENTS, THE MULTISCALE SELF-CONSISTENT SCHEME IS USED. THE MECHANICAL BEHAVIOR OF THE SINGLE CRYSTALS IS DESCRIBED BY A FINITE STRAIN RATE-INDEPENDENT CONSTITUTIVE FRAMEWORK, WHERE THE SCHMID LAW IS USED TO MODEL THE PLASTIC FLOW. THE CONDITION OF LOSS OF ELLIPTICITY AT THE MACROSCALE IS USED AS PLASTIC INSTABILITY CRITERION IN THE FE MODELING. THIS NUMERICAL APPROACH, WHICH COUPLES THE FE METHOD WITH THE SELF-CONSISTENT SCHEME, IS USED TO SIMULATE A DEEP DRAWING PROCESS, AND THE ABOVE CRITERION IS USED TO PREDICT THE FORMABILITY LIMIT OF THE STUDIED SHEETS DURING THIS OPERATION.