168 research outputs found
Stress Concentration and Mechanical Strength of Cubic Lattice Architectures
The continuous design of cubic lattice architecture materials provides a wide range of mechanical properties. It makes possible to control the stress magnitude and the local maxima in the structure. This study reveals some architectures specifically designed to reach a good compromise between mass reduction and mechanical strength. Decreased local stress concentration prevents the early occurrence of localized plasticity or damage, and promotes the fatigue resistance. The high performance of cubic architectures is reported extensively, and structures with the best damage resistance are identified. The fatigue resistance and SâN curves (stress magnitude versus lifetime curves) can be estimated successfully, based on the investigation of the stress concentration. The output data are represented in two-dimensional (2D) color maps to help mechanical engineers in selecting the suitable architecture with the desired stress concentration factor, and eventually with the correct fatigue lifetime
Martensite Transformation and Superelasticity at High Temperature of (TiHfZr)74(NbTa)26 High-Entropy Shape Memory Alloy
In this work, a (TiHfZr)(NbTa) 26 (%at) high-entropy quinary alloy has been developed especially for high-temperature superelastic applications and studied over a large range of temperatures. The mechanical properties of this new material were compared with those of other superelastic alloys. The different ingots have been made in a cold crucible from pure metals. Several thermomechanical treatments have been performed on the microstructure of four alloys among them (TiHfZr)(NbTa) 26 alloy. The microstructure of each alloy has been characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and x-ray diffraction technique (XRD) and the mechanical behavior was investigated through three-point bending tests between - 40 and 200C, in quasi-static monotonic and low cycle loading conditions. The effects of the thermomechanical treatments on the static and cyclic thermomechanical mechanical responses have been analyzed in combination with the microstructure investigations of the four studied alloys. It has been shown that the (TiHfZr)(NbTa) 26 alloy presents a martensitic transformation and a superelastic effect over the studied range of temperatures, in the cold-worked state or after solution treatment. Finally, the obtained experimental results have been compared with those of other superelastic alloys demonstrating the features of the developed high-entropy high-temperature superelastic alloy
A continuous crystallographic approach to generate cubic lattices and its effect on relative stiffness of architectured materials
This original work proposes to investigate the transposition of crystallography rules to cubic lattice architectured materials to generate new 3D porous structures. The application of symmetry operations provides a complete and convenient way to configure the lattice architecture with only two parameters. New lattice structures were created by slipping from the conventional Bravais lattice toward non-compact complex structures. The resulting stiffness of the porous materials was thoroughly evaluated for all the combinations of architecture parameters. This exhaustive study revealed attractive structures having high specific stiffness, up to twice as large as the usual octet-truss for a given relative density. It results in a relationship between effective Young modulus and relative density for any lattice structure. It also revealed the opportunity to generate auxetic structures at will, with a controlled Poisson ratio. The collection of the elastic properties for all the cubic structures into 3D maps provides a convenient tool for lattice materials design, for research, and for mechanical engineering. The resulting mechanical properties are highly variable according to architecture, and can be easily tailored for specific applications using the simple yet powerful formalism developed in this work.The authors acknowledge the financial support from French National Research Agency ANR (LabEx DAMAS, Grant no.ANR-11-LABX-0008-01)
Variations of the Elastic Properties of the CoCrFeMnNi High Entropy Alloy Deformed by Groove Cold Rolling
The variations of the mechanical properties of the CoCrFeMnNi high entropy alloy (HEA) during groove cold rolling process were investigated with the aim of understanding their correlation relationships with the crystallographic texture. Our study revealed divergences in the variations of the microhardness and yield strength measured from samples deformed by groove cold rolling and conventional cold rolling processes. The crystallographic texture analyzed by electron back scattered diffraction (EBSD) revealed a hybrid texture between those obtained by conventional rolling and drawing processes. Though the groove cold rolling process induced a marked strengthening effect in the CoCrFeMnNi HEA, the mechanical properties were also characterized by an unusual decrease of the Youngâs modulus as the applied groove cold rolled deformation increased up to about 0.5 before reaching a stabilized value. This decrease of the Youngâs modulus was attributed to the increased density of mobile dislocations induced by work hardening during groove cold rolling processing
Architectural effect on 3D elastic properties and anisotropy of cubic lattice structures
This article investigates the elastic properties of a large panel of lattice architectures using a continuous description of geometry. The elastic constants of the orthotropic material are determined, and discussed in terms of specific stiffness and of its density dependence. Different kind of topology families are emerging depending on their specific deformation behavior. For some of them, interesting properties in term of traction-compression were measured, while some other families are predominantly adapted to shear loading. Homogenization technique also allows to quantify the anisotropy of the structures and to compare them. Specific structures having quasi-isotropic properties even at low relative densities were detected. Experimental works demonstrated the validity of the numerical models, and highlighted the necessity to consider carefully the effect of defects on the specific strength, which are of the second-order however not negligible. Finally, this article provides user-friendly maps for selection of optimal architectures for a large variety of specific needs, like a target stiffness or anisotropy
Investigation and Composition Characterization of a âNiTi-likeâ Alloy Combining High Temperature Shape Memory and High Entropy
New high temperature shape memory alloyswith ïŹve or more elements are under development and present attractive performances for several functional applications. These active metallic materials are called high entropy and high temperature shape memory alloys (HE-HT-SMAs). This work deals with the characterization of an alloy that combines high temperature shape memory effect and high entropy effect features, a NiCuTiHfZr alloy. The evolution of the phase transformation and the shape memory effect during thermal fatigue was compared with a ternary alloy NiTiZr. Ingots were prepared in a cold crucible and alloys were characterized after thermal cycling at 600 K without a protective gas atmosphere. Optical microscope, X-ray diffraction, and scanning elec- tron microscopy observations showed the presence of martensite in this unpublished alloy at room temperature. The differential scanning calorimetry (DSC) tests showed that martensitic transformation takes place at high temperature. High temperature thermal cycling was performed during a three-point bending tests under constant load without a protective atmosphere. Thermomechanical results showed that high entropy effects increase the operating behavior at high temperature. Hence this new composition of NiCuTiHfZr alloy can be used as an actuator for aerospace and aeronautic application
Detection of epithelial apoptosis in pelvic ileal pouches for ulcerative colitis and familial adenomatous polyposis
<p>Abstract</p> <p>Background</p> <p>Ileal pouch-anal anastomosis (IPAA) is the surgical procedure of choice for patients with refractory ulcerative colitis (UC) and for familial adenomatous polyposis (FAP) with many rectal polyps. Pouchitis is one of the more frequent complications after IPAA in UC patients; however, it is rare in FAP.</p> <p>Objective</p> <p>Evaluate pro-apoptotic activity in endoscopically and histological normal mucosa of the ileal pouch in patients with UC and FAP.</p> <p>Methods</p> <p>Eighteen patients (nine with UC and nine with FAP) with J pouch after total rectocolectomy were studied. Biopsies were obtained from the mucosa of the pouch and from normal ileum. The specimens were snap-frozen and the expressions of Bax and Bcl-2 were determined by immunoblot of protein extracts and by immunohistochemistry analysis. FADD, Caspase-8, APAF-1 and Caspase-9 were evaluated by immunoprecipitation and immunoblot.</p> <p>Results</p> <p>Patients with UC had significantly higher protein levels of Bax and APAF-1, Caspase-9 than patients with FAP, but were similar to controls. The expressions of Bcl-2 and FADD, Caspase-8 were similar in the groups. Immunohistochemistry for Bax showed less intensity of immunoreactions in FAP than in UC and Controls. Bcl-2 immunostaining was similar among the groups.</p> <p>Conclusion</p> <p>Patients with FAP present lower levels of pro-apoptotic proteins in all methods applied, even in the absence of clinical and endoscopic pouchitis and dysplasia in the histological analysis. These findings may explain a tendency of up-regulation of apoptosis in UC patients, resulting in higher rates of progression to pouchitis in these patients, which could correlate with mucosal atrophy that occurs in inflamed tissue. However, FAP patients had low pro-apoptotic activity in the mucosa, and it could explain the tendency to low cell turn over and presence of adenomas in this syndrome.</p
T cell immunoengineering with advanced biomaterials
Recent advances in biomaterials design offer the potential to actively control immune cell activation and behaviour. Many human diseases, such as infections, cancer, and autoimmune disorders, are partly mediated by inappropriate or insufficient activation of the immune system. T cells play a central role in the host immune response to these diseases, and so constitute a promising cell type for manipulation. In vivo, T cells are stimulated by antigen presenting cells (APC), therefore to design immunoengineering biomaterials that control T cell behaviour, artificial interfaces that mimic the natural APC-T cell interaction are required. This review draws together research in the design and fabrication of such biomaterial interfaces, and highlights efforts to elucidate key parameters in T cell activation, such as substrate mechanical properties and spatial organization of receptors, illustrating how they can be manipulated by bioengineering approaches to alter T cell function
Matériaux mésostructurés et infiltration métallique avec optimisation du squelette architecturé
The constant search for structural lightening and performance optimization is at the origin of hybrid materials. They are defined as the combination of two (or more) materials, or the structuring of a material in a given volume, according to predetermined organization and scale in order to respond to a specific application. In addition, the recent growth of additive manufacturing offers a new unmatched design freedom. This is at the origin of hybrid materials such as lattices; it is an assembly of micro-beams ordered or not to fill a given volume. This PhD work focuses on the development of a hybrid metallic material with optimized architectured skeleton. At first, we will focus on the optimization of the skeleton. To do this, an original model generation of periodic lattices inspired by crystallography will be proposed. It will allow the generation of a database of structures to which will be added quasiperiodic lattices structures. In a second time, we will focus on the performances of these structures from the point of view of: mechanical behavior and porous network infiltration by a liquid. In both cases, phenomenological relations will be determined in order to relate the rigidity to the relative density, or the rise of an infiltration front according to the geometric characteristics of a skeleton. These relationships, via the parameters that govern them, make it possible to identify the influence of the topology and give rise to selection tools in the form of 2D maps. The X-ray tomography control steps, evaluations of the experimental mechanical properties and infiltration of porous networks make possible the confrontation with the proposed models. These different tools validate the topology and the scale of the optimized skeleton from the mechanical point of view and the infiltration. Finally, composites combining an aluminum alloy and a Ti-6Al-4V skeleton produced by selective laser melting are produced by a cold crucible, Porosity and metallurgical analysis at the Ti / Al interface will reveal the viability of the process, as well as the influence of the processing conditions on the microstructures.La recherche constante dâallĂ©gement de structure et dâoptimisation des performances est Ă lâorigine des matĂ©riaux hybrides. Ils sont dĂ©finis comme la combinaison de deux matĂ©riaux (ou plus), ou la structuration dâun matĂ©riau dans un volume donnĂ©, selon une organisation et une Ă©chelle prĂ©dĂ©terminĂ©e en vue de rĂ©pondre Ă une application spĂ©cifique. De plus, lâessor rĂ©cent de la fabrication additive permet dâentrevoir une libertĂ© de conception inĂ©galĂ©e. Ceci est Ă lâorigine de matĂ©riaux hybrides tels que les structures lattices ; il sâagit dâun assemblage de micro-poutres ordonnĂ©es ou non visant Ă remplir un volume donnĂ©. Ce travail de thĂšse porte sur lâĂ©laboration dâun matĂ©riau hybride mĂ©tallique Ă squelette architecturĂ© optimisĂ©. Dans un premier temps, nous nous intĂ©resserons Ă lâoptimisation du squelette. Pour ce faire un modĂšle original de gĂ©nĂ©ration de structures lattices pĂ©riodiques inspirĂ© de la cristallographie sera proposĂ©. Il permettra la gĂ©nĂ©ration dâune base de donnĂ©es de structures Ă laquelle seront ajoutĂ©es des structures lattices quasipĂ©riodiques. Dans un second temps, nous nous intĂ©resserons aux performances de ces structures du point de vue du comportement mĂ©canique et de lâinfiltration de rĂ©seau poreux par un liquide. Dans les deux cas, des relations phĂ©nomĂ©nologiques seront dĂ©terminĂ©es afin de relier la rigiditĂ© Ă la densitĂ© relative, ou la remontĂ© dâun front dâinfiltration en fonction des caractĂ©ristique gĂ©omĂ©trique dâun squelette. Ces relations, via les paramĂštres qui les gouvernent, permettent de dĂ©gager lâinfluence de la topologie et donne lieu Ă des outils de sĂ©lection sous forme de cartes 2D. Les Ă©tapes de contrĂŽle des structures par tomographie X, dâĂ©valuations des propriĂ©tĂ©s mĂ©caniques expĂ©rimentales et dâinfiltration de rĂ©seaux poreux, rendent possible la confrontation avec les modĂšles proposĂ©s. Ces diffĂ©rents outils valident la topologie et lâĂ©chelle du squelette optimisĂ© du point de vue mĂ©canique et de lâinfiltration. Pour finir, des composites associant un alliage dâaluminium et un squelette en Ti- 6Al-4V produit par fusion laser sĂ©lective, sont Ă©laborĂ©es par creuset froid. Une analyse des porositĂ©s et de la mĂ©tallurgie Ă lâinterface Ti/Al rĂ©vĂ©lera la viabilitĂ© du procĂ©dĂ©, ainsi que lâinfluence des conditions dâĂ©laborations sur les microstructures
Metal infiltrated mesostructured materials with opmitization of architectured scaffold
La recherche constante dâallĂ©gement de structure et dâoptimisation des performances est Ă lâorigine des matĂ©riaux hybrides. Ils sont dĂ©finis comme la combinaison de deux matĂ©riaux (ou plus), ou la structuration dâun matĂ©riau dans un volume donnĂ©, selon une organisation et une Ă©chelle prĂ©dĂ©terminĂ©e en vue de rĂ©pondre Ă une application spĂ©cifique. De plus, lâessor rĂ©cent de la fabrication additive permet dâentrevoir une libertĂ© de conception inĂ©galĂ©e. Ceci est Ă lâorigine de matĂ©riaux hybrides tels que les structures lattices ; il sâagit dâun assemblage de micro-poutres ordonnĂ©es ou non visant Ă remplir un volume donnĂ©. Ce travail de thĂšse porte sur lâĂ©laboration dâun matĂ©riau hybride mĂ©tallique Ă squelette architecturĂ© optimisĂ©. Dans un premier temps, nous nous intĂ©resserons Ă lâoptimisation du squelette. Pour ce faire un modĂšle original de gĂ©nĂ©ration de structures lattices pĂ©riodiques inspirĂ© de la cristallographie sera proposĂ©. Il permettra la gĂ©nĂ©ration dâune base de donnĂ©es de structures Ă laquelle seront ajoutĂ©es des structures lattices quasipĂ©riodiques. Dans un second temps, nous nous intĂ©resserons aux performances de ces structures du point de vue du comportement mĂ©canique et de lâinfiltration de rĂ©seau poreux par un liquide. Dans les deux cas, des relations phĂ©nomĂ©nologiques seront dĂ©terminĂ©es afin de relier la rigiditĂ© Ă la densitĂ© relative, ou la remontĂ© dâun front dâinfiltration en fonction des caractĂ©ristique gĂ©omĂ©trique dâun squelette. Ces relations, via les paramĂštres qui les gouvernent, permettent de dĂ©gager lâinfluence de la topologie et donne lieu Ă des outils de sĂ©lection sous forme de cartes 2D. Les Ă©tapes de contrĂŽle des structures par tomographie X, dâĂ©valuations des propriĂ©tĂ©s mĂ©caniques expĂ©rimentales et dâinfiltration de rĂ©seaux poreux, rendent possible la confrontation avec les modĂšles proposĂ©s. Ces diffĂ©rents outils valident la topologie et lâĂ©chelle du squelette optimisĂ© du point de vue mĂ©canique et de lâinfiltration. Pour finir, des composites associant un alliage dâaluminium et un squelette en Ti- 6Al-4V produit par fusion laser sĂ©lective, sont Ă©laborĂ©es par creuset froid. Une analyse des porositĂ©s et de la mĂ©tallurgie Ă lâinterface Ti/Al rĂ©vĂ©lera la viabilitĂ© du procĂ©dĂ©, ainsi que lâinfluence des conditions dâĂ©laborations sur les microstructures.The constant search for structural lightening and performance optimization is at the origin of hybrid materials. They are defined as the combination of two (or more) materials, or the structuring of a material in a given volume, according to predetermined organization and scale in order to respond to a specific application. In addition, the recent growth of additive manufacturing offers a new unmatched design freedom. This is at the origin of hybrid materials such as lattices; it is an assembly of micro-beams ordered or not to fill a given volume. This PhD work focuses on the development of a hybrid metallic material with optimized architectured skeleton. At first, we will focus on the optimization of the skeleton. To do this, an original model generation of periodic lattices inspired by crystallography will be proposed. It will allow the generation of a database of structures to which will be added quasiperiodic lattices structures. In a second time, we will focus on the performances of these structures from the point of view of: mechanical behavior and porous network infiltration by a liquid. In both cases, phenomenological relations will be determined in order to relate the rigidity to the relative density, or the rise of an infiltration front according to the geometric characteristics of a skeleton. These relationships, via the parameters that govern them, make it possible to identify the influence of the topology and give rise to selection tools in the form of 2D maps. The X-ray tomography control steps, evaluations of the experimental mechanical properties and infiltration of porous networks make possible the confrontation with the proposed models. These different tools validate the topology and the scale of the optimized skeleton from the mechanical point of view and the infiltration. Finally, composites combining an aluminum alloy and a Ti-6Al-4V skeleton produced by selective laser melting are produced by a cold crucible, Porosity and metallurgical analysis at the Ti / Al interface will reveal the viability of the process, as well as the influence of the processing conditions on the microstructures
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