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1. Kasemer, Matthew Paul. A Framework for Modeling Discrete Deformation Twinning in Hexagonal Crystals.

Degree: PhD, Mechanical Engineering, 2018, Cornell University

Modeling the plastic deformation of metals has historically been achieved by considering only crystallographic slip, the dominant mode of plastic deformation. While sufficient for materials that deform primarily by means of slip, many metals may exhibit other modes of plastic deformation, and thus may not be accurately modeled by slip alone. Deformation twinning is another mode of plastic deformation, characterized by a rapid, large uniform shear of a discrete region of material, coupled with a reorientation of the crystal lattice within said region. While witnessed in metals of various crystal symmetries, metals comprised of hexagonal crystals are especially prone to exhibit twinning, as they may require twinning to accommodate generalized plasticity. Due in large part to limitations in computational capabilities, models have often ignored deformation twinning. Existing models rely on the homogenization of the responses due to both slip and twinning via a modified Taylor hypothesis, and thus fail to predict accurate local states. Additionally, these models consider twin systems as modified slip systems, obscuring the discrete nature of deformation twinning, as well as the disparity in relative speeds at which each deformation mode propagates. Advances in computational capabilities and model frameworks have allowed for the possibility to study this deformation mode in more detail. A parallelized finite element framework is uniquely suited to approach this problem, as a proven platform for modeling high fidelity, finely discretized representations of polycrystalline aggregates. A framework is presented, in which grains within a microstructure are pre-discretized - based on their crystallographic orientation - into discrete regions that may deform by deformation twinning. A boundary value problem is solved, in which the displacement of the nodes within a twin region are rapidly mapped to their twinned location, the region's crystal lattice is reoriented via three separate schemes, and the remainder of the body deforms by means of crystallographic slip to accommodate this deformation. In this way, the extended framework retains the characteristic differences between crystallographic slip and deformation twinning in a way that existing models do not. Work is calculated due to the changes in local environments due to twinning. Changes in local stress states are discussed in light of global and local work measures and various parameters, including twin size and reorientation schemes. Advisors/Committee Members: Dawson, Paul Richard (chair), Baker, Shefford P. (committee member), Miller, Matthew Peter (committee member).

Subjects/Keywords: Crystal Plasticity; Mechanical engineering; Finite element method; Hexagonal symmetry; Solid mechanics; Twinning

…for a magnesium-titanium alloy with hexagonal crystal symmetry (reproduced from [… …calculated from entire EBSD scan as well as selected regions, and plotted in the hexagonal symmetry… …selection plotted in the hexagonal symmetry fundamental region of Rodrigues’ space. Scales… …that exhibit either cubic or hexagonal symmetry. Hexagonal close packed crystals are… …Framework . . . . . . . . 2 Background 2.1 Deformation of Hexagonal Crystals . . . . 2.1.1 Slip… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Kasemer, M. P. (2018). A Framework for Modeling Discrete Deformation Twinning in Hexagonal Crystals. (Doctoral Dissertation). Cornell University. Retrieved from http://hdl.handle.net/1813/59581

Chicago Manual of Style (16th Edition):

Kasemer, Matthew Paul. “A Framework for Modeling Discrete Deformation Twinning in Hexagonal Crystals.” 2018. Doctoral Dissertation, Cornell University. Accessed November 27, 2020. http://hdl.handle.net/1813/59581.

MLA Handbook (7th Edition):

Kasemer, Matthew Paul. “A Framework for Modeling Discrete Deformation Twinning in Hexagonal Crystals.” 2018. Web. 27 Nov 2020.

Vancouver:

Kasemer MP. A Framework for Modeling Discrete Deformation Twinning in Hexagonal Crystals. [Internet] [Doctoral dissertation]. Cornell University; 2018. [cited 2020 Nov 27]. Available from: http://hdl.handle.net/1813/59581.

Council of Science Editors:

Kasemer MP. A Framework for Modeling Discrete Deformation Twinning in Hexagonal Crystals. [Doctoral Dissertation]. Cornell University; 2018. Available from: http://hdl.handle.net/1813/59581


Université de Lorraine

2. Son, Sébastien. Organogels et aérogels obtenus à partir de phénylalanine : étude de l'organisation supramoléculaire et élaboration d'un nouveau type de super-isolant thermique : Organogels and aerogels obtained from phenylalanine : Study of the supermolecular organization and elaboration of a new kind of super heat insulator.

Degree: Docteur es, Génie des procédés et des produits, 2015, Université de Lorraine

Depuis 1973, l’un des objectifs principaux de la France est la diminution de la consommation des énergies de chauffage des bâtiments du résidentiel et du tertiaire qui représentent plus de 40% de la consommation énergétique totale du pays. Le développement des isolants thermiques a été par conséquent un sujet de recherche qui a abouti à de nouveaux matériaux : les super-isolants thermiques de conductivité thermique inférieure à 25 mW.m-1.K-1. Les aérogels organiques de faible densité de Z-Phe-NH-Napht étudiés au LCPM présentent une structure fibrillaire qui leur confère des propriétés thermiques intéressantes malgré une résistance mécanique faible. Une étude fondamentale de l’organisation supramoléculaire nous a permis d’une part de démontrer l’existence de deux modes d’empilement des molécules organogélatrices : tête-à-tête (monocristaux) et tête-à-queue (gels), caractérisées par une signature infrarouge propre à des pseudo-cycles respectivement en C12 et C10/C14. D’autre part, nous avons étudié le mécanisme de formation séquentiel de ces gels et abouti à un modèle complet d’organisation de la molécule isolée à la fibre basé sur une symétrie hexagonale. En vue d’une commercialisation d’un isolant à base d’aérogel organique, nous avons tout d’abord optimisé le protocole d’obtention des aérogels pour ensuite travailler à l’amélioration des propriétés thermiques et mécaniques. Nous sommes parvenus à un nouvel isolant hydrophobe présentant une conductivité thermique de l’ordre de celles des super-isolants et de bonnes propriétés mécaniques compatibles avec les pré-requis industriels pour une application dans le bâtiment

Since 1973, France's main objective in this domain has been to reduce the consumption of energy in heating residential and industrial buildings, which represents more than 40% of the national consumption. Consequently, the development of heat insulators has been the subject of research which has resulted in new materials: super thermal insulators with a thermal conductivity of less than 25 mW.m-1.K-1. Organic aerogels with a low density of Z-Phe-NH-Napht have been studied at LCPM for the past 10 years. Despite their very weak mechanical resistance they present a fibrillar structure which gives them very interesting thermal properties. A fundamental study of the supermolecular self-assembly allowed us to demonstrate the existence of two stacking methods of gelling molecules: head-to-head (monocrystals) and head-to-tail (gels) which are characterized by a specific infrared signature to the pseudo-cycles respectively on C12 and C10/C14. In addition, we also studied the sequential formation mechanism of these gels which resulted in a full model of their molecular organization from the single molecule to the fiber and based on a hexagonal packing symmetry. In aim of commercializing an insulator made from organic aerogels, we firstly optimized the protocol for obtaining aerogels to then work on improving their thermal and mechanical properties. We created a new hydrophobic insulator which has both a thermal…

Advisors/Committee Members: Jamart, Brigitte (thesis director).

Subjects/Keywords: Conductivité thermique; Isolant thermique; Aérogel de faible poids moléculaire; Organisation supramoléculaire; Empilement tête-À-Tête ou tête-À-Queue; Signature infrarouge de pseudo-Cycles C10 et C12-C14; Symétrie hexagonale; Super-Isolant thermique; Thermal conductivity; Thermal properties; Low molecular weight aerogel; Supermolecular self-Assembly; Head-To-Head and head-To-Tail stacking; C12/C10-C14 pseudo-Cycles infrared signatures; Hexagonal packing symmetry; Super thermal insulator; 620.11; 541.345

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Son, S. (2015). Organogels et aérogels obtenus à partir de phénylalanine : étude de l'organisation supramoléculaire et élaboration d'un nouveau type de super-isolant thermique : Organogels and aerogels obtained from phenylalanine : Study of the supermolecular organization and elaboration of a new kind of super heat insulator. (Doctoral Dissertation). Université de Lorraine. Retrieved from http://www.theses.fr/2015LORR0004

Chicago Manual of Style (16th Edition):

Son, Sébastien. “Organogels et aérogels obtenus à partir de phénylalanine : étude de l'organisation supramoléculaire et élaboration d'un nouveau type de super-isolant thermique : Organogels and aerogels obtained from phenylalanine : Study of the supermolecular organization and elaboration of a new kind of super heat insulator.” 2015. Doctoral Dissertation, Université de Lorraine. Accessed November 27, 2020. http://www.theses.fr/2015LORR0004.

MLA Handbook (7th Edition):

Son, Sébastien. “Organogels et aérogels obtenus à partir de phénylalanine : étude de l'organisation supramoléculaire et élaboration d'un nouveau type de super-isolant thermique : Organogels and aerogels obtained from phenylalanine : Study of the supermolecular organization and elaboration of a new kind of super heat insulator.” 2015. Web. 27 Nov 2020.

Vancouver:

Son S. Organogels et aérogels obtenus à partir de phénylalanine : étude de l'organisation supramoléculaire et élaboration d'un nouveau type de super-isolant thermique : Organogels and aerogels obtained from phenylalanine : Study of the supermolecular organization and elaboration of a new kind of super heat insulator. [Internet] [Doctoral dissertation]. Université de Lorraine; 2015. [cited 2020 Nov 27]. Available from: http://www.theses.fr/2015LORR0004.

Council of Science Editors:

Son S. Organogels et aérogels obtenus à partir de phénylalanine : étude de l'organisation supramoléculaire et élaboration d'un nouveau type de super-isolant thermique : Organogels and aerogels obtained from phenylalanine : Study of the supermolecular organization and elaboration of a new kind of super heat insulator. [Doctoral Dissertation]. Université de Lorraine; 2015. Available from: http://www.theses.fr/2015LORR0004

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