published_or_final_version / abstract / Civil Engineering / Master / Master of Philosophy

Abstract not available

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19308号 / 工博第4105号 / 新制||工||1633(附属図書館) / 32310 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 辻 伸泰, 教授 白井 泰治, 教授 乾 晴行 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The addition of rare earth (RE) alloying elements is a promising method for improving the strength, ductility and overall formability of magnesium (Mg) alloys. However, the underlying mechanism for this phenomenon remains unclear. An investigation on the effect of the rare earth element, scandium (Sc), on binary Mg-Sc alloys has been pursued. Tension and compression tests were performed on a series of dilute binary Mg-Sc alloys at temperatures of 298 K, 78 K and 4.2 K. As a reference, pure Mg was also investigated for comparative purposes. Differences in tension and compression stress-strain curves highlighted distinct activated mechanisms, where slip dominated in tension and twinning governed compression. The observed increase in ductility and prolonged necking was attributed to a weaker basal texture, enhanced twinning and non-basal slip. A decreased work hardening rate suggests an improvement in dislocation recovery with Sc addition. In compression, Mg-Sc alloys followed Fleischer’s theory of solution hardening, where stress scales with concentration, c, as c^1/2; however, there was a very weak fit with both Fleischer and Labusch models under tension. The strengthening rate displayed by Mg-Sc was relatively weak compared to previously studied Mg-RE systems. However, considering the estimated misfit parameters, the size and modulus misfit was not enough to account for the strengthening rate. The results suggest that hardening of the twinning mode may influence strength. Constitutive modelling, based on a self-consistent plasticity model, was used to characterize the deformation behaviour. The simulations predicted an increased relative activity of non-basal <c+a> slip with Sc addition, supporting experimental results and proposed mechanisms in literature. The results of Mg-Sc alloys have been connected to theories that identify a decrease in stacking fault energy (SFE) as the determining factor for increased strength and ductility of Mg-RE alloys. A comparison of the SFE of previously studied REEs with Sc, demonstrated strong evidence towards the theory’s validity. Sc has been shown to only moderately reduce the SFE of Mg and hence, the present experimental results have shown a moderate increase in strength and ductility. Additional modelling and detailed dislocation analysis are suggested as future steps to further support this theory. / Thesis / Master of Applied Science (MASc)

The amount of total and relative sway of a framed or a composite (frame-shear wall) building is of utmost importance in assessing the seismic resistance of the building. Therefore, the design engineer must calculate the sway profile of the building several times during the design process. However, it is not a simple task to calculate the sway of a three-dimensional structure. Of course, computer programs can do the job, but developing the three-dimensional model becomes necessary, which is obviously tedious and time consuming. An easy to apply analytical method is developed, which enables the determination of sway profiles of framed and composite buildings subject to seismic loading. Various framed and composite three-dimensional buildings subject to lateral seismic loads are solved by SAP2000 and the proposed analytical method. The sway profiles are compared and found to be in very good agreement. In most cases, the amount of error involved is less than 5 %. The analytical method is applied to determine sway magnitudes at any desired elevation of the building, the relative sway between two consecutive floors, the slope at any desired point along the height and the curvature distribution of the building from foundation to roof level. After sway and sway-related properties are known, the requirements of the Turkish Earthquake Code can be evaluated and / or checked. By using the analytical method, the amount of shear walls necessary to satisfy Turkish Earthquake Code requirements are determined. Thus, a vital design question has been answered, which up till present time, could only be met by rough empirical guidelines. A mathematical derivation is presented to satisfy the strength requirement of a three-dimensional composite building subject to seismic loading. Thus, the occurrence of shear failure before moment failure in the building is securely avoided. A design procedure is developed to satisfy the stiffness requirement of composite buildings subject to lateral seismic loading. Some useful tools, such as executable user-friendly programs written by using &ldquo / Borland Delphi&rdquo / , have been developed to make the analysis and design easy for the engineer. A method is also developed to satisfy the ductility requirement of composite buildings subject to lateral seismic loading based on a plastic analysis. The commonly accepted sway ductility of &amp / #956 / &amp / #916 / =5 has been used and successful seismic energy dissipation is thus obtained.