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Unformatted text preview: Torsion Testing by Patrick McAdams Laboratory Section AA, Tuesday 2:30 p.m., January 30, 2007 Daniel Flores Date of Laboratory: February 5, 2007 Report Submitted to: Jiangyu Li EXECUTIVE SUMMARY A torsion test was conducted on constant diameter 6061-T6 aluminum and A36 steel samples with a Technovate torsion test machine. This machine allows samples to be fixed on one end and twisted to any angle one the other. Force and angle of twist were recorded for each sample until fracture occurred. With this data, the aluminum and the steel were plotted against each other for analysis of difference in material property and behavior. The aluminum data was plotted against two estimation models: the Power Hardening Model and the Ramberg-Osgood Model. These values were compared with measured values of torque to determine how accurate each estimation method was. Neither was very accurate as the Power Hardening Model and the Ramberg-Osgood Model yielded 14.3% and 34.2% error, respectively. The Power Hardening Model is clearly more accurate, but it is not tremendously accurate. This was assumed to be due to a bending moment that may have occurred within the sample due to loading. The fracture displayed evidence of a bending moment or a material flaw at the fracture point. Since the sample seemed to be slightly bent during loading and the initially longitudinal lines were uniform throughout the sample, it was assumed that the failure was more likely due to a bending moment. In the end it was recommended that strength coefficients and strain hardening components be determined from the data to account for any bending moments or material flaws. It was also recommended that more samples be tested for each material to standardize results. OBJECTIVES Torsion in a rod is a rotational force which twists a member around a neutral axis. Understanding torsion is an important concept to understand within engineering, because there are many engineering applications which rely on it. This lab will examine a stationary rod which is subjected to torque. While the material is linear-elastic and the shear stress is below the shear yielding point, torque can be determined using angle of twist, Hookes Law, and the torsion formula. At shear stresses above the point of yielding, however, the torsion formula will no longer be valid and the material will have a non-linear relationship between torque and angle of twist. While this occurs, the specimen will experience both elastic and plastic deformation. This lab will examine the Power Hardening (PH) Model and the Ramberg-Osgood (RO) Model as they apply to torsion. The PH model applies to the plastic region while the RO model applies to the entire region before failure. They will be used to estimate torque in a 6061-T6 aluminum sample. The results from these estimation methods will be plotted against measured values....
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This note was uploaded on 04/08/2008 for the course ME 354 taught by Professor Jiangyuli during the Winter '07 term at University of Washington.
- Winter '07