An automated hydraulic bulge tester

Abstract

The hydraulic bulge test is used to determine stress-strain properties of sheet metal under biaxial tension. A major advantage of the 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 processes. An automated bulge test unit is described which enables true stress-true strain data to be obtained under controlled strain rates up to high levels of plastic deformation. Typical bulge test stress-strain curves are presented for a variety of sheet alloys and compared with tensile curves. The paper describes the theoretical basis for the test, the equipment for deforming the specimen, the measuring unit and the data processing system. A detailed examination of systematic errors in a unit of this kind is presented. The results indicate that the stress-strain curve is found with this equipment to be within acceptable limits of accuracy. 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 to high levels of strain such as alloys for drawn and ironed can manufacture and automotive applications of aluminum sheet.