The design and performance of a machine for testing sheet material in the plastic range is described. The material is stressed in uniform biaxial tension by means of the hydrostatic bulge test. Test variables are measured by electrical transducers and an analogue unit is employed to permit autographic recording of the diagram relating true stress and natural strain. Closed-loop control of the rate of straining is achieved with an electro-hydraulic actuator; the feedback signal is derived from the analogue unit and the test can be controlled on the basis of a computed parameter such as true stress or natural strain.
BellR.DuncanJ. L.JohnsonW.‘The evaluation of a prototype machine for automatically recording the true stress-strain curve for sheet material using the hydrostatic bulge test’, Advances in machine tool design and research (Proc. 5th Int. Mach. Tool Design Res. Conf., 1964) 1965, 411 (Pergamon Press Ltd, Oxford).
3.
JohnsonW.DuncanJ. L.‘The use of the biaxial test extensometer’, Sh. Metal Inds196542, 271.
4.
HawardR. N.Private communication.
5.
HarpurN. F.‘Some design considerations of hydraulic servos of jack type’, Conf. Hydraulic Servomechanisms1953, 41 (Institution of Mechanical Engineers, London).
6.
EcklundK.‘Graphic solution for cubic system damping’, Control Engng19596 (No. 6), 111 (Data file 27).
