Tube free bulging experiment with force-end and material properties testing

Compared with uniaxial tension, the material property parameters obtained by tube bulging test (TBT) can accurately reflect the plastic forming properties of materials under high-pressure fluid condition. Different end-conditions will seriously affect the experiment results of TBT. According to the defects of existed experimental method and equipment internationally, a special TBT system, with accurate boundary conditions and loading units, was successfully designed and developed. The axial force, axial displacement, and the internal pressure are the key points of the system which could be accurately controlled in real-time bycontrol strategy of displacement under dynamic active loading state and proportional servo valves. The free sliding of fixed tube ends was implemented by a special designed fixture. During the experimental process, the real-time thickness and bulging height in the pole, and the real-time internal pressure were monitored by the ultrasonic thickness gauge, the magnetostrictive displacement sensor and the ultra-high pressure sensor. The stress-strain curve and material properties were derived by the Swift material constitutive model and the monitor data. The experimental data demonstrate that the two load balance conditions, which are the balance of two axial forces with internal pressure and the balance of two axial contractive displacements, are always satisfied during all the test process. The test data processing results show that the monitor data have good repeatability and can be used to get the material properties.