Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15312号 / 工博第3191号 / 新制||工||1480(附属図書館) / 27790 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 井合 進, 教授 田村 武, 教授 岡 二三生 / 学位規則第4条第1項該当

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15646号 / 工博第3304号 / 新制||工||1499(附属図書館) / 28183 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 岡 二三生, 教授 勝見 武, 准教授 木元 小百合 / 学位規則第4条第1項該当

Dans un contexte mondial d’accroissement de la demande en travaux souterrains en sites urbains, l’ingénieur doit disposer d’outils et de méthodes performants pour concevoir des ouvrages sûrs, à risques évalués et maîtrisés. La prévision des tassements provoqués par le creusement de tunnels en site urbain repose largement sur des méthodes empiriques. Dans ce mémoire, on propose une méthode de prévision des tassements pour des tunnels creusés par la méthode conventionnelle avec présoutènements. Cette méthode est basée sur des modèles éléments finis tridimensionnels avec CESAR-LCPC. On s’intéresse d’abord aux spécificités des tunnels urbains, et aux limites des différentes méthodes empiriques et numériques. On introduit ensuite une loi de comportement du sol qui combine une élasticité non-linéaire et une isotropie transverse. Le modèle reproduit le profil, notamment la largeur, des cuvettes de tassements empiriques de référence et facilite les études de sensibilité. Le dimensionnement des présoutènements, boulons en fibre de verre et voûte parapluie, est ensuite décrit pour la maîtrise des tassements. La dernière partie est une étude de cas d’une conception par analyse de risques d’un ouvrage représentatif du contexte du Grand Paris Express / In a context of increasing demand for underground works in urban areas worldwide, the engineers must have efficient tools and methods to design safe structures, with assessed and managed risks. The prediction of settlements due to urban tunnelling is mainly made with empirical methods. In this dissertation, we propose a method of settlements prediction for tunnels built using conventional methods (i.e. without TBM), with reinforcements. This method is based on three dimensional finite element models with CESAR-LCPC. In the first place, we present the specificities of urban tunnels, and the limitations of numerical and empirical methods. Then, we introduce a constitutive model for the soil which combines a non-linear elasticity and a cross-anisotropic behaviour. This model reproduces the shape, and especially the width, of the reference empirical settlement troughs and permits easy sensitivity analysis. The design of reinforcements, fibreglass bolts and umbrella arches, is then described for the purpose of reducing the settlements. The last section is a case study of risk analysis design for a tunnel typical for the context of the Grand Paris Express project

In an effort to help understand the mechanical properties of human platelets, their deformations were measured using micropipette experiments over an aspiration pressure range of 1-5 cmH2O, in steps of 1 cmH2O. The experiments confirmed the previously reported linear relationship between deformation and pressure. The experimental results were used to determine the material constants of a thin-axisymmetric shell model based on a strain-energy constitutive relation to describe the platelet deformations under aspiration. The model was successful in capturing the experimental deformations. It also suggested that the mechanical properties of human platelets are not significantly influenced by their volumes, but do vary depending on the platelets’ undeformed shape ratios. In addition, the model suggested that platelet membrane ruptures due to micropipette aspiration may be strain-related. The limitations of the experimental methods arising from direct contact with reactive cells such as platelets are highlighted, prompting the need for developing new methods which will not require the use of inhibition agents that alter the platelets’ mechanical properties. Afin d’approfondir les connaissances des propriétés mécaniques des plaquettes humaines, leurs déformations ont été mesurées lors d’expériences avec des micropipettes pour des pressions d’aspiration de 1-5 cmH2O, par intervalles de 1 cmH2O. Les expériences ont confirmé la relation linéaire entre les déformations et la pression d’aspiration telle que précédemment publié. Les données expérimentales ont été utilisées pour déterminer les constantes matérielles d’un modèle de membrane mince axisymétrique basé sur une loi de comportement caractérisant l’énergie de déformation. Le modèle simule bien les déformations des plaquettes sous aspiration; il suggère également que les propriétés mécaniques des plaquettes humaines ne sont pas influencées significativement leur volume, mais varient en fonction de leurs formes avant déformation. De plus, le modèle suggère que les ruptures de la membrane des plaquettes sous aspiration seraient reliées aux déformations. Les limites des méthodes expérimentales utilisées, du fait du contact direct avec des cellules aussi réactives que les plaquettes sont soulignées, et mettent l’emphase sur le besoin de mettre au point de nouvelles méthodes ne requérant pas d’agents d’inhibitions qui altèrent les propriétés mécaniques des plaquettes.

Modelling and simulation of the human body during an impact situation such as a car accident, can lead to better designed safety features on vehicles. In order to achieve this, investigation into the material properties and the creation of a numerical model of cortical bone is needed. One approach to creating a material model of cortical bone suitable for these situations is to describe the material model as visco-elastic, as reported by Shim et al. [1], Bekker et al. [2] and Cloete et al. [3]. The work by Shim et al. and Bekker et al. developed three-dimensional models, but do not accurately capture the transition in behaviour in the intermediate strain rate region, while Cloete et al. developed a phenomenological model which captures the intermediate strain rate behaviour in one dimension. This work aims to verify and extend these models. The intermediate strain rate regime (1 s−1 to 100 s−1 ) is of particular interest because it is a key characteristic of the behaviour of cortical bone and several studies have been conducted to gather experimental data in this region [3, 4, 5, 6]. The behaviour can be captured using non-linear viscoelastic models. This dissertation focuses on the development and implementation of a material model of cortical bone based on non-linear visco-elastic models to capture the intermediate strain rate regime behaviour. The material model was developed using uni-axial test results from cortical bone. The model by Cloete et al. has been improved and extended, and issues of local and global strain rate with regards to the viscosity have been clarified. A hereditary integral approach was taken in the analysis and implementation of discrete models and was found to be consistent with mathematical models. The model developed was extended to three dimensions in a manner similar to that of Shim et al. and Bekker et al. for implementation in commercial finite element software (LS-Dyna and Abaqus).

We introduce an elastic constitutive model of gravity that enables the interpretation of cosmological observations in terms of established ideas from Solid Mechanics and multiscale modeling. The behavior of physical space is identified with that of a material-like medium called "cosmic fabric," which exhibits constitutive behavior. This cosmic fabric is a solid hyperplate that is broad in the three ordinary spatial dimensions and thin in a fourth hyperspatial dimension. Matter in space is treated as fabric inclusions that prescribe in-plane (three-dimensional) strain causing the transverse bending of the fabric into the fourth hyperspatial dimension. The linearized Einstein-Hilbert action, which governs the dynamics of physical space, is derived from postulating Hooke’s Law for the fabric, and the Schwarzschild metric is recovered from investigating matterabric interactions. At the continuum length scale, the Principle of Relativity is shown to apply for both moving and stationary observers alike, so that the fabric’s rest reference frame remains observationally indistinguishable at such a length scale. Within the Cosmic Fabric paradigm, the structural properties of space at different hierarchical length scales can be investigated using theoretical notions and computational tools from solid mechanics to address outstanding problems in cosmology and fundamental physics. For example, we propose and offer theoretical support for the "Inherent Structure Hypothesis", which states that the gravitational anomalies currently attributed to dark matter may in fact be manifestations of the inherent (undeformed) curvature of space. In addition, we develop a numerical framework wherein one can perform numerical "experiments" to investigate the implications of said hypothesis.

The present study develops a phenomenological adaptation to an internal state variable (ISV) model that incorporates the influence of dynamic recrystallization (DRX) in a material’s evolving microstructure and flow stress response. During metal forming and joining processes that promote internal heat distributions and large strains, microstructural processes often occur that result in a transformation of the evolving microstructure away from the base distribution. In an effort to lower the stored energy accumulated in the material’s lattice and grain structure, the deformed material may undergo a type of dynamic recovery process, such as DRX. In this study, the ISV model’s flow stress output is modified to include a phenomenological DRX softening and hardening term internal to the isotropic hardening rate ISV. The flow stress thus directly includes the influence of microstructure evolution. The evolving grain size is modeled such that an inverse relation exists between strain hardening and average grain size.

Constitutive modeling is a method that is useful in providing precise predictions of material response in components subjected to a variety of operating conditions. A process for optimizing the material constants of the Miller constitutive model for uniaxial modeling was developed and implemented in an automated optimization routine. Generally, up to twenty experiments simulating a range of conditions are needed to identify the material parameters for the model. The research sought to minimize the amount of empirical data that is necessary for optimization, aiming to reduce the costs and time necessary to carry out this procedure for more expensive classes of materials. The ultimate goal was to develop a robust method for determining the material constants of a viscoplastic model using a minimum amount of experimental data. An automated optimization routine was implemented into a program, referred to as uSHARP, developed as part of the research to determine constitutive model parameters. Central to the method was the use of more complex stress, strain, and temperature histories than are traditionally used, allowing for the effects of all material parameters to be captured using as few tests as possible. By carrying out successive finite element simulations and comparing the results to simulated experimental test data, the material constants were determined from 75% fewer experiments. By reducing monetary costs and time required, this procedure will allow for a more widespread application of advanced constitutive models in industry, allowing for better life prediction modeling of critical components in high temperature applications.

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