Design of a hydraulic bulge test apparatus

Abstract

The various equi-biaxial tension tests for sheet metal were studied and compared to determine the most appropriate equipping in the Impact and Crashworthiness Laboratory, MIT, for the testing of Advanced High Strength Steel. The hydraulic bulge test was identified as the most economical solution. The equipment was designed to accommodate material strength of up to 1000MPa with plate thickness between 1.0mm and 1.8mm. The design process is explained in detail with focus on the challenges faced. The closed-form solution for the hydraulic bulge test was also derived. Two methods of deriving the stress-strain relationship in the material were also proposed. The first method uses the optical measuring system to determine displacement and surface strain distribution. The second method uses geometrical approximations and dome height measurements. A new experimental technique and step-by-step procedure were also developed. Tests were successfully conducted using galvanized steel to demonstrate the effectiveness of the hydraulic bulge test apparatus in achieving the equi-biaxial stress state in sheet metal.