CET 345W Materials Testing Laboratory -Experiment3

When torque is applied to a part of a machine there is a transmission of power by shafts and machine members. The buildup of torque results in the build-up of shear stress within the power-transmitting member. If the sha ...

When torque is applied to a part of a machine there is a transmission of power by shafts and machine members. The buildup of torque results in the build-up of shear stress within the power-transmitting member. If the shaft is not properly designed, it may fail due to the torsional force. The torsional test is performed to investigate the shearing properties of both solid and hollow specimen however, it cannot be performed on brittle materials and requires correction factors for shapes other than circular sections. In this experiment, the torsional test will be used to investigate shearing properties of a mild steel bar. The torsion test will provide the necessary information to understand the shearing stress-strain relationship. There should be a relationship shown between the modulus of rigidity and the tensile modulus of elasticity. The necessary information should be provided to also find ductility and modulus of rupture through the torsion formula. 2. Procedure I. Tool Identification and Setup 1. Draw a permanent line using a permanent marker down the length of the steel rod. 2. Measure the diameter of the rod three times with the digital micrometer zeroing the micrometer before each measurement. Record the average of the three diameters. 3. Remove the safety cover from the Tinius Olsen 10K Torsion machine. 4. Place the steel rod in the fixed rotor of the torsion machine. 5. Tighten the fixed rotor’s chuck grips using the Allen Key to secure the steel rod. Make sure that the teeth indicators line up on the concentric rings. 6. Once the rod is secure, adjust the movable rotor so that it connects with the free side of the steel rod. 7. Repeat step five for the moveable rotor. 8. Before turning on the torsion machine, apply a small amount of torque using the clamping knob to ensure that the troptometer is indicating the proper angle of twist without slip. 9. Replace the safety cover and power on the torsion machine. II. Applying Torsion 1. Configure the Tinius Olsen 10K Torsion Machine for testing. a. Select the MENU button on the 602 Controller. b. Select MACHINE CONTROL on the 602 MAIN MENU. c. Select SPEEDS on the MACHINE CONTROL MENU. d. Verify that “Speed1” and “Speed2” read “+10.0 deg/min” and then select MENU. e. Select Zero Force, Zero Pos., and Zero Aux. f. Select TEST. g. Select the increase load button (▲). 2. Observe and record the first ten readings. 3. Observe increased speed of +60.02 degree per minute. 4. Observ ..................................................................................................continued