NUMERICAL AND EXPERIMENTAL INVESTIGATION OF FORMING LIMIT DIAGRAMS OF 6063 ALUMINUM ALLOY SHEETS USING AYADA DUCTILE FRACTURE CRITERION AND THE SECOND DERIVATIVE OF LARGE STRAIN CRITERION AT INCREASED TEMPERATURES

Abstract

THE PRESENT STUDY INVESTIGATED THE FORMING LIMIT DIAGRAMS OF ALUMINUM ALLOY 6063 SHEETS USING NUMERICAL AND EXPERIMENTAL METHODS AT INCREASED TEMPERATURES. IN THE NUMERICAL SECTION, FOR THE FIRST TIME, THE AYADA DUCTILE FRACTURE CRITERION AND THE SECOND DERIVATIVE OF THE LARGE STRAIN CRITERION WERE USED. ABAQUS FINITE ELEMENT ANALYSIS SOFTWARE WAS EMPLOYED FOR THE SIMULATIONS. IN ORDER TO DETERMINE NECKING TIME, AFTER SIMULATION, RELEVANT DATA SUCH AS STRESS HISTORY, MAIN STRESSES, EQUIVALENT STRAIN HISTORY, AND LARGE STRAIN WERE EXTRACTED AND THE CONDITIONS FOR THE NECKING CRITERIA WERE INVESTIGATED. TO OBTAIN THE FORMING LIMIT DIAGRAMS IN THE EXPERIMENTAL PART, A NAKAZIMA FORMAT WAS USED. EXPERIMENTS WERE CONDUCTED AT TEMPERATURES OF 25, 150, 200 AND 250 DEGREES CELSIUS FOR THE SAMPLES WITH EQUAL LENGTHS AND DIFFERENT WIDTHS. AYADA CRITERION HAD BETTER COMPATIBILITY WITH THE LEFT SIDE OF THE FORMING DIAGRAMS (FOR SMALL NEGATIVE STRAINS), WHILE THE SECOND DERIVATIVE OF THE LARGE STRAIN CRITERION HAD BETTER COMPATIBILITY WITH THE RIGHT SIDE OF THE DIAGRAMS (FOR SMALL POSITIVE STRAINS). THE RESULTS ALSO SHOWED THAT WITH THE INCREASE IN TEMPERATURE, THE FORMING DIAGRAM MOVED UPWARD AND SHEET FORMING WAS IMPROVED. THIS IMPROVEMENT WAS ALMOST SIMILAR FOR THE TEMPERATURES OF 150 AND 200ºC, WHILE THE PROCESSING TEMPERATURE OF 250ºC LED TO SIGNIFICANT IMPROVEMENT IN FORMING, AS COMPARED TO OTHER TEMPERATURES.