A new apparatus for studying mechanical behavior under pressure

Using a servohydraulic intensifier, a servohydraulic universal test machine and a novel test chamber, pressures of 750 MPa and axial stresses of almost any magnitude are simultaneously generated and applied to the gage section of a solid, cylindrical specimen. Under combined axial-stress/external-pressure loadings, a solid specimen experiences a truly three-dimensional, homogeneous stress state in which the axial stress equals σ1 and the radial and circumferential stresses equal the negative of the pressure, -P. Through independent computer control of the pressure and axial stress, material behavior under monotonically and cyclically applied multiaxial stresses are investigated. This paper describes the experimental details of the test chamber design, high-pressure fluid production and sealing, load and strain measurement under high pressure, computer control and data acquisition. Experimental results obtained from triaxial monotonic tests on low alloy steel and triaxial cyclic tests on a Ni-Ti alloy using this unique apparatus are presented.