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Student Number : 9102778K - MSc(Eng) dissertation - School of Chemical and Metallurgical Engineering - Faculty of Engineering and the Built Environment / Strain ageing anisotropy, a surprising property of iron, implies that interstitials, which are non-lattice obstacles, can give non-symmetrical opposition to glide. Al- though this has been investigated by others, it is shown that it is di±cult to eliminate extraneous residual stresses during testing. An Avery torsion machine was adapted for the study of strain ageing anisotropy through the design of a torque and twist measurement system. This required the optimization of sensitivity, stiffness and me- chanical stability criteria, while ensuring practicality. When a ¯ne-grained sample with circumferential groove was tested a sharp yield point and lack of yield after ageing in the reverse direction was observed. Although more testing is required, it con¯rms the results of other researchers. In testing it was found that the quality of the sample machining was critical in achieving an accurate yield, and the groove design must be reviewed and improved. While the system measured to the required torque resolution, the strain measurement system could be improved by redesign and better calibration statistics.

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As a candidate for dynamic electric contacts, Nano-twinned copper has intrinsic conductivity and enhanced fretting resistance. To better understand its general mechanical behavior, we conduct molecular dynamics simulation studies to investigate responses of nano-twinned copper to stress and to one-directional and two-directional sliding processes, in comparison with single crystal and nano-grained model systems. Obtained results suggest that the twin boundary blocks dislocation movement more effectively and the degree of emitting dislocations under stress is considerably lower than that of grain boundary. The inverse H-P relation only occurring in nano-grained materials does not necessarily result from grain boundary sliding. Under sliding conditions, dislocations are easier to be generated in the single crystal system. During the two-directional sliding process, Bauschinger effect is observed in the single crystal and nano-twinned systems, while the situation is opposite for the nano-grained system. The nano-twinned Cu shows the least dislocation accumulation during two-directional sliding. / Materials Engineering

The main purpose with this investigation was to clarify when or if specific grades will soften or harden during the straightening process in a seven roll cross roll straightening machine. The aim was solely made to include tubes which had been cold worked to achieve high yield strength levels. The straightening process will induce lengthwise tensile and compressive stress and strain. According to theory straightening could therefore also induce considerable Bauschinger effect.  Physical tests, with material from pilgered tubes, in a laboratory environment were performed to give a well-defined set up of the strain levels and sign of the same. Real in process trials were also performed. Parallel to the physical laboratory tests and the real process tests a FEM-simulation and a FEM-model to calculate strain levels was developed.  Two material types were investigated, but the results are only unambiguous for material A. Further investigations need to be done on material B to give a clear picture.

<p> A yield criterion depending on stress, strain and their histories is revised so as to achieve better correlation with experimental data. It is shown that this simple criterion exhibits a reasonable Bauschinger effect. Theoretical expressions for revised yield stresses for two different types of tests are derived for this function. </p> <p> The purpose of the experimental work in this thesis was to determine the degree of correlation between the proposed function and experimental data. Two types of tests were carried out. The first test was essentially for evaluating the constants appearing in the yield criterion. These values of constants were then used to predict the gross tensile stress-strain curves for specimens cut from sheets which had undergone plastic bending in one direction and contained residual stresses prior to tensile loading. An approximate method to calculate these residual stresses is also outlined. </p> <p> Conclusions are deduced by comparing the experimental and theoretical results for these tests and suggestions are made for future research. </p> / Thesis / Master of Engineering (ME)

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 144-155).

In this work, the Bauschinger effect is shown to be intimately tied not only to plasticity but to damage as well. The plasticity-damage effect on the Bauschinger effect is demonstrated by employing different definitions (Bauschinger Stress Parameter, Bauschinger Effect Parameter, the Ratio of Forward-to-Reverse Yield, and the Ratio of Kinematic-to-Isotropic Hardening) for two differently processed aluminum alloys (rolled and cast) in which specimens were tested to different prestrain levels under tension and compression. Damage progression from second phase particles and inclusions that were generally equiaxed for the cast A356-T6 aluminum alloy and elongated for the rolled 7075 aluminum alloy was quantified from interrupted experiments. Observations showed that the Bauschinger effect had larger values for compression prestrains when compared to tension. The Bauschinger effect was also found to be a function of damage to particles/inclusions, dislocation/particle interaction, the work hardening rate, and the Bauschinger effect definition.

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