Univ., Habil-Schr.--Leipzig, 2002. / Literaturverzeichnis S. [201] - 209.

Thesis (Ph. D.)--University of Hong Kong, 1998. / Includes bibliographical references.

Thesis (M.S.) in Civil and Environmental Engineering--University of Maine, 2002. / Includes vita. Includes bibliographical references (leaves 90-92).

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references. Also available in electronic version.

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The influence of different microstructural attributes on the material properties such strength, hardness, residual stress or other physical properties are very well understood. During the manufacturing of mechanical parts utilized in important industries such as energy, aerospace or biomedical, the effect of the processing in term of thermal and mechanical loading is very important as it is directly influencing the microstructure evolution and the properties. The understanding of how the manufacturing process such as high precision machining will affect first the microstructure and therefore the part properties. In this work, we propose the Materials-Affected Manufacturing (MAM). It is a new paradigm helping to understand the interaction between the manufacturing process parameters, materials microstructure attributes and the properties. This is solved using a computational approach using an iterative blending to relate different models. Residual stresses are also studied. An enhanced analytical model is proposed. The model is capable for the first time to predict analytically the residual stress regeneration in the multi-step machining problem. An enhancement of the existing model is proposed. The (MAM) method was applied to the case of turning process of Aluminum 7075. The average grain size and the crystallographic texture were predicted and validated experimentally. The residual stress regeneration was computed for the case of milling of Aluminum 2024. Experimental validations using X-ray technique were performed for validations.

Depending on the material system and machining conditions, the localized strain, strain rate and temperature fields induced to the material during the machining process can be intense. Therefore, a wide variety of microstructural evolutions are likely to occur below the machined surface. These microstructural changes take place at various scales. First of all, due to the severe plastic deformation below the machined surface, the crystallographic orientation of grains can change dramatically. In addition, if the levels of the induced temperature and strain are high enough, recrystallization may occur, new grains may form and subsequently grow. Additionally, contingent upon the duration of the machining process, partial grain growth might also happen. Last but not least, if the material is consisted of more than one phase, the microstructural characteristics of secondary phases will also evolve. The ultimate result of all the aforementioned evolutions produces remarkable changes in the mechanical and thermal (and almost all other) properties of the material, which consequently affect the response of the material during service. A comprehensive modeling framework that reliably captures all the aspects of the above microstructural evolutions in machining is absent in the open literature. This work coalesces concrete and all-inclusive modeling toolsets into a unified scheme to follow the mentioned phenomena in machining of aluminum alloy 7075. The modeling outcomes are verified by experimental results to assure reliability. Finite element analyses were applied to obtain the stress, temperature, strain and strain rate fields developed in the material during machining at different parameters. Kinetic-based models were exploited to determine the possible recrystallization or grain growth. A viscoplastic self-consistent crystal plasticity model was utilized to investigate texture evolution below the machined surface. Also for multi-phase materials, the first steps in developing a totally new constitutive model to yield the extent of the possible refinement in the second phase precipitates, were taken. The main goal of the work was to link the above-mentioned microstructural evolutions to process parameters of machining by mathematical derivation of process path functions. Therefore, prediction of microstructural changes as a result of changing the process parameters became possible; which has significant industrial potential and importance. Additionally, such a direct and complete linkage between machining and microstructure is completely new to the scientific community in manufacturing and design fields.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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