Many metals used in modern engineering exhibit anisotropy. A common assumption when modelling anisotropic metals is that the level of anisotropy is fixed throughout the calculation. As it is well understood that processes such as cold rolling, forging or shock loading change the level of anisotropy, it is clear that this assumption is not accurate when dealing with large deformations. The aim of this project was to develop a tool capable to predict large deformations of a single crystal or crystalline aggregate of a metal of interest and able to trace an evolution of anisotropy within the material. The outcome of this project is a verified computational tool capable of predicting large deformations in metals. This computational tool is built on the Crystal Plasticity Finite Element Method (CPFEM). The CPFEM in this project is an implementation of an existing constitutive model, based on the crystal plasticity theory (the single crystal strength model), into the framework of the FEA software DYNA3D® . Accuracy of the new tool was validated for a large deformation of a single crystal of an annealed OFHC copper at room temperature. The implementation was also tested for a large deformation of a polycrystalline aggregate comprised of 512 crystals of an annealed anisotropic OFHC copper in a uniaxial compression and tension test. Here sufficient agreement with the experimental data was not achieved and further investigation was proposed in order to find out the cause of the discrepancy. Moreover, the behaviour of anisotropic metals during a large deformation was modelled and it was demonstrated that this tool is able to trace the evolution of anisotropy. The main benefit of having this computational tool lies in virtual material testing. This testing has the advantage over experiments in time and cost expenses. This tool and its future improvements, which were proposed, will allow studying evolution of anisotropy in FCC and BCC materials during dynamic finite deformations, which can lead to current material models improvement.

This thesis describes the effect of dislocation slip on superplastic deformation of AZ31 magnesium alloy. Through two different routes of ECAE (equal channel angular extrusion), two types of specimens having the same grain size but different texture were obtained. One is favorable for basal slip and the other is not. Under the same condition of deformation, the strain rate sensitivity and contribution of grain boundary sliding to total elongation in these two different specimens are almost the same. As for elongation, not much difference was found. The present results demonstrate that the relationship between dislocation slip and grain boundary sliding in superplastic AZ31 magnesium alloy is non-obvious.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23891号 / 工博第4978号 / 新制||工||1777(附属図書館) / 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 乾 晴行, 教授 安田 秀幸 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

In this present work, the dynamics of deformation mechanisms activated in binary magnesium-gadolinium alloys with respect to amount of Gd were investigated with in-situ experimental methods. Cast alloys are characterized by random texture. Compression test were done at room temperature with simultaneous record of acoustic emission response. The acoustic emission signal was subsequently analysed using advanced clustering method providing information about the dominant deformation mechanisms. High speed camera was used to study the dynamics of twinning, including estimation of the velocity of twin propagation with respect to Gd concentration. The deformation tests were repeated in a chamber of scanning electron microscope (in-situ SEM) with concurrent following the microstructure development using secondary electrons and electron back-scattered diffraction (EBSD) in different stages of the deformation. Main goal of this measurements was to identify active slip systems and the progress of twin volume fraction during deformation. Keywords: magnesium alloy, deformation tests, acoustic emission, high-speed camera, electron microscopy, twinning

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