A novel small specimen testing method based on a pneumatic bulging test: Measurement of tensile properties at high temperatures

Abstract

A novel testing method based on a pneumatic bulging test (PBT) was proposed to measure the tensile strength of round-disc-shaped miniature specimens at high temperatures. As an alternative to the small punch test (SPT) method, the concentrated force loaded by the punch was replaced with the uniformly distributed pressure loaded by high-pressure argon. A unique PBT apparatus was developed. Bulging test on specimens of SUS 304 stainless steel were carried out at 600 °C. The results show that the maximum deflection due to the bulge is located at the region of the pole of the deformed specimen, and it was also the place where the cracks initiated. Formulas are developed to forecast the instantaneous radius of curvature and thickness at the pole during the deformation process. Furthermore, the tensile strength and yield strength of the material at high temperatures were determined using the pressure−deflection curve at the pole and recommended equations. Verified with data from the uniaxial tensile experiment, the PBT method was proven to be a reliable testing technique for assessing tensile properties at high temperatures using miniature specimens. With a good physical similarity in failure mode, eccentricity-free loading, and reduced impact of contact friction from loading, the PBT technique has promising potential for future applications in the determination of high temperature strength of materials.