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Unformatted text preview: Introduction Specimens of steel 1045, aluminum 6061, and PMMA will be submitted to a four-point bending test in which an Instron model 4400 machine will apply a gradually increasing load of up to 100kN on the specimens. Through the four- point bending test, the yield load ( P y ) , maximum load ( P max ) and modulus of rupture in bending ( R B ) will be calculated. The yield load ( P y ) is the load at which irreversible plastic deformation begins to occur, while the modulus of rupture in bending ( R B ) is defined as the maximum fiber stress at failure. Also, a torsion test on aluminum 6061 and PMMA will be conducted on specimens of circular cross-sections by means of a gear-driven torsion machine. The torsion machine will measure the applied moment applied to the specimen and the relative angle of rotation will be obtained from the test. Through the torsion test data, the yield torque ( T y ), maximum torque ( T max ), modulus of rupture in torsion ( R T ), and shear modulus ( G ) will be obtained for both materials tested. The yield torque ( T y ) is the amount of torque exerted on a specimen before plastic deformation commences, the modulus of rupture in torsion ( R T ) represents the maximum shear stress in the extreme fiber of a circular member at failure, while the shear modulus ( G ) is a measure of the stiffness of a material when subjected to a twist loading. The Young’s modulus ( E ) and yield strength ( σ y ) for each material will also be derived from both the torsion and bending tests and compared to values obtained from tensile and compressive tests. Material properties obtained in bending and torsion tests prove very useful as design parameters. For example, manufacturers of drive shafts for motor vehicles must use materials that have a high enough modulus of rupture in torsion in order to not to fail when the maximum torque is applied to the drive shaft. The yield torque is considered as well to avoid plastic deformation of the driveshaft which could, in turn, affect performance. Procedure Beams of steel 1045, aluminum 6061 and PMMA with rectangular cross sections were used in the four-point bending test. Prior to performing the test, the width and depth of each bending specimen was measured three times and averaged. The moment arm was also verified by indirectly measuring the spacing of the centers of the rollers on the Instron 4400 machine. The beam was then centered and aligned in the testing position on the machine. After the testing apparatus was prepared and the data-acquisition system was programmed to record load versus position data at regular time intervals, the specimen was loaded. Due to potential damage of the bending apparatus, each specimen was loaded to a maximum deformation of ten millimeters. After the maximum deformation was reached the specimen was removed and the radius of curvature was measured using a chart. The final width at the top and bottom of the specimen was also measured and recorded. Since the PMMA specimen recorded....
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This lab report was uploaded on 04/20/2008 for the course GE 312 taught by Professor Reis during the Spring '06 term at University of Illinois at Urbana–Champaign.
- Spring '06