Experimental and numerical investigations of the sheet hydraulic bulge test for aluminum alloys

The bulge test has been identified as a standard method for obtaining stress-strain relationships through large plastic strain in biaxial tension and the utilization of this information in formability assessment. A major advantage of the hydraulic bulge test over the more conventional uniaxial tensile test is that the stress-strain curve extends to the range of effective strain found in many forming applications. However dynamic measurement of various parameters during the sheet metal bulge test poses a challenge and requires specially designed and customized equipment and not to mention careful attention to detail in order to get accurate results. Typical bulge test stress-strain curves are presented for a variety of aluminum sheet alloys and compared with tensile curves obtained from similar tests conducted by 'Aluminum Company of America' (ALCOA). This study describes the theoretical basis for the test, the test equipment, the measurement system, the data processing system and the various challenges faced during the testing process and how it was overcome. The study also describes a numerical simulation for the sheet metal hydroforming using the explicit finite element code LS-Dyna 3D and the results compared to the experimental results. It is anticipated that a facility of this kind will have wide application in studying the basic behavior of sheet alloys, particularly those which must be formed at high levels of strain such as alloys used in manufacturing and automotive applications of aluminum sheet.