No description available.

<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)

" Sample cutting is an important minimally invasive medical procedure. Currently there are several types of medical devices used to cut a distal biological sample, for example, a video endoscope and TurboHawk Plaque Excision Systems. Directional Atherectomy (DA) with the TurboHawk Plaque Excision Systems is a catheter-based, minimally invasive treatment method for peripheral arterial disease (PAD). During a procedure, a catheter is directed toward an area of plaque buildup to remove the plaque from the body, restoring blood flow (Covidien, 2013). Endoscopy is an important procedure used in the medical field to study and diagnose different parts of a body without the need to undergo a major surgery. The major devices are a video endoscope with a flexible or rigid insertion tube and endoscopic therapy devices. Arrays of the devices, through the instrument channel in the insertion tube of endoscopes, to perform a variety of functions are offered. The biological sample cut is one of the important endoscopic therapies. Both of Directional Atherectomy and endoscopy procedures require a power transmission from the proximal tip of device to the distal end, where the cutter is located, for cutting a sample. However, the working length is up to meters, and the diameter of the devices is in millimeter scale in the minimally invasive surgery. Thus enough power transmitting to the distal end of the device for the biological sample cutting is crucial. This research presents the effort toward the investigation of the potential power mechanisms from the proximal tip to the cutter at the distal end of the device for rapid rotational cutting motion to improve the cutting efficiency and accuracy. In this thesis, the potential powering mechanisms including fluid, electrical, and torque coils are investigated. Since the transmission power is used for a rotational cutting action, and the cutting geometry has influence on the cutting power, thus this research also focuses on the analysis of the cutting geometry for the rotational sample cutting. The Hertz contact theory and von Mises yield criterion are used to find the influence of tool geometry on the material removing process, as well as Abaqus, a commercial FEM software, is used for the finite element analysis. Fiber-reinforced composite structures are the main characteristic of the representative biological sample, and their mechanical behavior is strongly influenced by the concentration and structural arrangement of constitute such as collagen and elastin. Researches show that the biological sample, for example, a soft biological sample, has hyperelastic properties and behave anisotropically, and there are a few publications about the plastic properties and cutting mechanics. Thus a linear elastic and linear plastic material model is defined for the finite element analysis of material removal. The analytical results and finite element results both show that as the tool rake angle increases or the tool angle decreases, the magnitude of cutting force decreases. A preliminary representative sample cutting experiment was conducted, and standard cutters with different cutting geometries were tested in order to find the characteristic of the biological sample cutting and the influence of tool geometry on the required cutting power. The experiments reveal the same conclusions as the analytical and finite element results. "

<p>This report is a review on aspects of constitutive modelling of high strength steels. Aspects that have been presented are basic crystallography of steel, martensite transformation, thermodynamics and plasticity from a phenomenological point of view. The phenomenon called mechanical twinning is reviewed and the properties of a new material type called TWIP-steel have been briefly presented. Focus has been given on phenomenological models and methods, but an overview over multiscale methods has also been given.</p>

This report is a review on aspects of constitutive modelling of high strength steels. Aspects that have been presented are basic crystallography of steel, martensite transformation, thermodynamics and plasticity from a phenomenological point of view. The phenomenon called mechanical twinning is reviewed and the properties of a new material type called TWIP-steel have been briefly presented. Focus has been given on phenomenological models and methods, but an overview over multiscale methods has also been given.

Woven structures are steadily emerging as excellent reinforcing components in dualphase composite materials subjected to multiaxial loads, thermal shock, and aggressive reactants in the environment. Metallic woven wire mesh materials display good ductility and relatively high specific strength and specific resilience. While use of this class of materials is rapidly expanding, significant gaps in mechanical behavior classification remain. This thesis works to address the mechanics of material knowledge gap that exists for characterizing the behavior of a metallic woven structure, composed of stainless steel wires on the order of 25 microns in diameter, and subjected to various loading conditions and stress risers. Uniaxial and biaxial tensile experiments, employing Digital Image Correlation (DIC) as a strain measurement tool, are conducted on woven wire mesh specimens incised in various material orientations, and with various notch geometries. Experimental results, supported by an ample analytic modeling effort, indicate that an orthotropic elastic constitutive model is reasonably capable of governing the macro-scale elasticity of the subject material. Also, the Stress Concentration Factor (SCF) associated with various notch geometries is documented experimentally and analytically, and it is shown that the degree of stress concentration is dependent on both notch and material orientation. The Finite Element Method (FEM) is employed on the macro-scale to expand the experimental test matrix, and to judge the effects of a homogenization assumption when modeling metallic woven structures. Additionally, plasticity of the stainless steel woven wire mesh is considered through experimental determination of the yield surface, and a thorough analytic modeling effort resulting in a modified form of the Hill yield criterion. Finally, mesoscale plasticity of the woven structure is considered, and the form of a multi-scale failure criterion is proposed and exercised numerically.

No description available.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23456号 / 理博第4750号 / 新制||理||1681(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 山路 敦, 准教授 佐藤 活志, 教授 生形 貴男 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Os processos de conformação de chapas metálicas são largamente usados na fabricação de produtos em diversas áreas, desde partes aeronáuticas a utensílios domésticos, devido a sua alta produtividade, confiabilidade e baixo custo de produção. Para se atingir tais qualidades, o desenvolvimento de um produto conformado deve levar em consideração os fatores metalúrgicos da chapa a ser usada. As chapas são geralmente produzidas por laminação a frio, o que as levam ter propriedades mecânicas distintas em relação à direção de laminação. Para modelar esta anisotropia, vários critérios de escoamento foram propostos. A fim de verificar a influência do critério de escoamento na distribuição de deformação no produto conformado, este trabalho teve como objetivo implementar os critérios de Hill (1979) e de Barlat et al. (1993) em um programa acadêmico que modela o processo de conformação de chapas via o método dos elementos finitos. O critério de Hill (1979) foi implementado e apresentou bons resultados, em acordo com a literatura. O critério de Barlat et al. (1993) foi deduzido em sua formulação para elementos finitos, embora não implementado. Com o critério de Hill (1979) foi possível analisar a distribuição da deformação para várias superfícies de escoamento, alterando-se apenas o valor de um parâmetro da função de escoamento. / The sheet metal forming processes are widely used in the manufacturing of products in several areas, from aviation to household utensils, due to its high productivity, reliability and low cost of production. To achieve these qualities, the design of a product made by sheet metal forming should take into consideration the metallurgical factors of the blank to be used. The blank is usually cold-rolled, which leads to different mechanical properties in the rolled and transverse directions. To take into account this anisotropy, several yield criteria were proposed. To check the influence of the yield criterion in the strain distribution of the final product, this study focused on the implementation of the yield criteria of Hill (1979) and Barlat et al. (1993) in an academic computer program that modeled the sheet metal forming process by the finite element method. The Hill (1979) criterion was implemented and had good results, in accordance with the literature. The Barlat et al. (1993) criterion was formulated for a finite element method analysis, though not implemented. By using Hill\'s non-quadratic yield criterion it was possible to analyze the strain distribution for various yield surfaces, changing only the value of one parameter of the yield function.

Os processos de conformação de chapas metálicas são largamente usados na fabricação de produtos em diversas áreas, desde partes aeronáuticas a utensílios domésticos, devido a sua alta produtividade, confiabilidade e baixo custo de produção. Para se atingir tais qualidades, o desenvolvimento de um produto conformado deve levar em consideração os fatores metalúrgicos da chapa a ser usada. As chapas são geralmente produzidas por laminação a frio, o que as levam ter propriedades mecânicas distintas em relação à direção de laminação. Para modelar esta anisotropia, vários critérios de escoamento foram propostos. A fim de verificar a influência do critério de escoamento na distribuição de deformação no produto conformado, este trabalho teve como objetivo implementar os critérios de Hill (1979) e de Barlat et al. (1993) em um programa acadêmico que modela o processo de conformação de chapas via o método dos elementos finitos. O critério de Hill (1979) foi implementado e apresentou bons resultados, em acordo com a literatura. O critério de Barlat et al. (1993) foi deduzido em sua formulação para elementos finitos, embora não implementado. Com o critério de Hill (1979) foi possível analisar a distribuição da deformação para várias superfícies de escoamento, alterando-se apenas o valor de um parâmetro da função de escoamento. / The sheet metal forming processes are widely used in the manufacturing of products in several areas, from aviation to household utensils, due to its high productivity, reliability and low cost of production. To achieve these qualities, the design of a product made by sheet metal forming should take into consideration the metallurgical factors of the blank to be used. The blank is usually cold-rolled, which leads to different mechanical properties in the rolled and transverse directions. To take into account this anisotropy, several yield criteria were proposed. To check the influence of the yield criterion in the strain distribution of the final product, this study focused on the implementation of the yield criteria of Hill (1979) and Barlat et al. (1993) in an academic computer program that modeled the sheet metal forming process by the finite element method. The Hill (1979) criterion was implemented and had good results, in accordance with the literature. The Barlat et al. (1993) criterion was formulated for a finite element method analysis, though not implemented. By using Hill\'s non-quadratic yield criterion it was possible to analyze the strain distribution for various yield surfaces, changing only the value of one parameter of the yield function.