Construction and validation tests of a torsion test machine

摘要

Present work aimed at developing, testing and operating a computerized prototype machine for performing cold plastic torsion tests. The operation and project of this machine were earned out in the Laboratory of Metal Forming at UDESC, Joinville. The equipment consists of a horizontal torsion machine composed of an electric motor, a wheel, a horizontal shaft and a control and acquisition data system. An encoder obtains the torsion angle and the torque is measured by a load cell. Experimental tests were carried out at a constant angular speed that imposed a constant shear strain rate to the test specimen. Setting the rotation speed to 60RPM, it was possible to simulate the initial operation stage of sheet metal rolling process that utilizes strain rate of about 2 s~(-1). The torsion tests have been performed on annealed materials such as 1020 steel, brass, pure copper and pure aluminum. The strain rate sensitivity parameter m has been evaluated from the equivalent stress versus strain curve from tensile and torsion tests. The parameter m from tensile tests for brass and copper were 0, however, for 1020 steel and aluminum were 0.013 and 0.027, respectively. In torsion tests the m-values were 0.072 and 0.045 for steel and brass. The fracture mechanisms were investigated in the rapture surface using the scanning electron microscope. The main observed fracture mechanism for these metals was coalescence of pores and shear bands.