A NOVEL METHOD FOR TENSILE TESTING OF SMALL DIAMETERNEEDLES
Abstract
A new specimen-type has been described for tensile testing of small 32G diameter needles. Specifically, tensile specimens of 32G thin-walled stainless steel cannulae (outside diameter: 237 µm, inside diameter: 167 µm) were successfully tested in a Instron® machine. The specimens were prepared by covering the ends of the 32G cannulae by larger 25G cannulae (outside diameter: 514 µm, inside diameter: 260 µm), and soldering the ends of thinwalled cannulae. The soldered parts formed the grip sections in the Instron® machine. Uniaxial tensile tests were carried out with different cannulae lengths to ensure that the stress-strain relationship is independent of the length, and the deformation is contained within the 32G thin-walled cannulae section. At the end of the tensile test, the specimens broke within the 32G cannulae and not at the soldered joints, thereby indicating a firm bonding between the different diameters metal parts. Since the cannulae were reinforced from the outside instead from the inside, it is expected that such a sample preparation for tensile testing can be extended to finer gages of cannulae.
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