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Littérature scientifique sur le sujet « Higher-gradient theorie »

Auteur : Grafiati

Publié le 9 mars 2023

Mis à jour le 10 mars 2023

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Articles de revues sur le sujet "Higher-gradient theorie"

Abali, B. Emek, Wolfgang H. Müller et Francesco dell’Isola. « Theory and computation of higher gradient elasticity theories based on action principles ». Archive of Applied Mechanics 87, n^o 9 (5 juin 2017) : 1495–510. http://dx.doi.org/10.1007/s00419-017-1266-5.

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Surana, Karan S., et Stephen W. Long. « Ordered Rate Constitutive Theories for Non-Classical Thermofluids Based on Convected Time Derivatives of the Strain and Higher Order Rotation Rate Tensors Using Entropy Inequality ». Entropy 22, n^o 4 (14 avril 2020) : 443. http://dx.doi.org/10.3390/e22040443.

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This paper considers non-classical continuum theory for thermoviscous fluids without memory incorporating internal rotation rates resulting from the antisymmetric part of the velocity gradient tensor to derive ordered rate constitutive theories for the Cauchy stress and the Cauchy moment tensor based on entropy inequality and representation theorem. Using the generalization of the conjugate pairs in the entropy inequality, the ordered rate constitutive theory for Cauchy stress tensor considers convected time derivatives of the Green’s strain tensor (or Almansi strain tensor) of up to orders n ε as its argument tensors and the ordered rate constitutive theory for the Cauchy moment tensor considers convected time derivatives of the symmetric part of the rotation gradient tensor up to orders n Θ . While the convected time derivatives of the strain tensors are well known the convected time derivatives of higher orders of the symmetric part of the rotation gradient tensor need to be derived and are presented in this paper. Complete and general constitutive theories based on integrity using conjugate pairs in the entropy inequality and the generalization of the argument tensors of the constitutive variables and the representation theorem are derived and the material coefficients are established. It is shown that for the type of non-classical thermofluids considered in this paper the dissipation mechanism is an ordered rate mechanism due to convected time derivatives of the strain tensor as well as the convected time derivatives of the symmetric part of the rotation gradient tensor. The derivations of the constitutive theories presented in the paper is basis independent but can be made basis specific depending upon the choice of the specific basis for the constitutive variables and the argument tensors. Simplified linear theories are also presented as subset of the general constitutive theories and are compared with published works.

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dell’Isola, F., P. Seppecher et A. Della Corte. « The postulations á la D’Alembert and á la Cauchy for higher gradient continuum theories are equivalent : a review of existing results ». Proceedings of the Royal Society A : Mathematical, Physical and Engineering Sciences 471, n^o 2183 (novembre 2015) : 20150415. http://dx.doi.org/10.1098/rspa.2015.0415.

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In order to found continuum mechanics, two different postulations have been used. The first, introduced by Lagrange and Piola, starts by postulating how the work expended by internal interactions in a body depends on the virtual velocity field and its gradients. Then, by using the divergence theorem, a representation theorem is found for the volume and contact interactions which can be exerted at the boundary of the considered body. This method assumes an a priori notion of internal work, regards stress tensors as dual of virtual displacements and their gradients, deduces the concept of contact interactions and produces their representation in terms of stresses using integration by parts. The second method, conceived by Cauchy and based on the celebrated tetrahedron argument, starts by postulating the type of contact interactions which can be exerted on the boundary of every (suitably) regular part of a body. Then it proceeds by proving the existence of stress tensors from a balance-type postulate. In this paper, we review some relevant literature on the subject, discussing how the two postulations can be reconciled in the case of higher gradient theories. Finally, we underline the importance of the concept of contact surface, edge and wedge s -order forces.

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GUHA, SUMAN, SANDEEP SANGAL et SUMIT BASU. « A review of higher order strain gradient theories of plasticity : Origins, thermodynamics and connections with dislocation mechanics ». Sadhana 40, n^o 4 (juin 2015) : 1205–40. http://dx.doi.org/10.1007/s12046-015-0369-3.

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Bardenhagen, S., et N. Triantafyllidis. « Derivation of higher order gradient continuum theories in 2,3-d non-linear elasticity from periodic lattice models ». Journal of the Mechanics and Physics of Solids 42, n^o 1 (janvier 1994) : 111–39. http://dx.doi.org/10.1016/0022-5096(94)90051-5.

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Miandoab, Ehsan Maani, Hossein Nejat Pishkenari et Aghil Yousefi-Koma. « Dynamic Analysis of Electrostatically Actuated Nanobeam Based on Strain Gradient Theory ». International Journal of Structural Stability and Dynamics 15, n^o 04 (mai 2015) : 1450059. http://dx.doi.org/10.1142/s021945541450059x.

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In this study, dynamic response of a micro- and nanobeams under electrostatic actuation is investigated using strain gradient theory. To solve the governing sixth-order partial differential equation, mode shapes and natural frequencies of beam using Euler–Bernoulli and strain gradient theories are derived and then compared with classical theory. Galerkin projection is utilized to convert the partial differential equation to ordinary differential equations representing the system mode shapes. Accuracy of proposed one degree of freedom model is verified by comparing the dynamic response of the electrostatically actuated micro-beam with analogue equation and differential quadrature methods. Moreover, the static pull-in voltages of micro-beams found by one DOF model are compared with the reported data in literature. The main advantage of proposed method based on the Galerkin method is its simplicity and also its low computational cost in analyzing the dynamic and static responses of micro- and nanobeams. Additionally, effect of axial force, beam thickness and applied voltage are analyzed. The results obtained based on strain gradient theory, are compared with classical and modified couple stress theories which are the special cases of the strain gradient theory. It is shown that strain gradient theory leads to higher frequency and lower amplitude in comparison with two other theories.

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Forest, Samuel, et Karam Sab. « Finite-deformation second-order micromorphic theory and its relations to strain and stress gradient models ». Mathematics and Mechanics of Solids 25, n^o 7 (1 août 2017) : 1429–49. http://dx.doi.org/10.1177/1081286517720844.

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Germain’s general micromorphic theory of order [Formula: see text] is extended to fully non-symmetric higher-order tensor degrees of freedom. An interpretation of the microdeformation kinematic variables as relaxed higher-order gradients of the displacement field is proposed. Dynamical balance laws and hyperelastic constitutive equations are derived within the finite deformation framework. Internal constraints are enforced to recover strain gradient theories of grade [Formula: see text]. An extension to finite deformations of a recently developed stress gradient continuum theory is then presented, together with its relation to the second-order micromorphic model. The linearization of the combination of stress and strain gradient models is then shown to deliver formulations related to Eringen’s and Aifantis’s well-known gradient models involving the Laplacians of stress and strain tensors. Finally, the structures of the dynamical equations are given for strain and stress gradient media, showing fundamental differences in the dynamical behaviour of these two classes of generalized continua.

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Panteghini, Andrea, et Lorenzo Bardella. « On the Finite Element implementation of higher-order gradient plasticity, with focus on theories based on plastic distortion incompatibility ». Computer Methods in Applied Mechanics and Engineering 310 (octobre 2016) : 840–65. http://dx.doi.org/10.1016/j.cma.2016.07.045.

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Polizzotto, Castrenze. « A note on the higher order strain and stress tensors within deformation gradient elasticity theories : Physical interpretations and comparisons ». International Journal of Solids and Structures 90 (juillet 2016) : 116–21. http://dx.doi.org/10.1016/j.ijsolstr.2016.04.001.

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Forest, Samuel. « Continuum thermomechanics of nonlinear micromorphic, strain and stress gradient media ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 378, n^o 2170 (30 mars 2020) : 20190169. http://dx.doi.org/10.1098/rsta.2019.0169.

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A comprehensive constitutive theory for the thermo-mechanical behaviour of generalized continua is established within the framework of continuum thermodynamics of irreversible processes. It represents an extension of the class of generalized standard materials to higher order and higher grade continuum theories. It reconciles most existing frameworks and proposes some new extensions for micromorphic and strain gradient media. The special case of strain gradient plasticity is also included as a contribution to the current debate on the consideration of energetic and dissipative mechanisms. Finally, the stress gradient continuum theory emerges as a new research field for which an elastic-viscoplastic theory at finite deformations is provided for the first time. This article is part of the theme issue ‘Fundamental aspects of nonequilibrium thermodynamics’.

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Thèses sur le sujet "Higher-gradient theorie"

GIUSTERI, GIULIO GIUSEPPE. « Higher-grandient theories for fluids and concentrated effects ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2012. http://hdl.handle.net/10281/28154.

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I consider the Virtual Power framework for Continuum Mechanics, which has recently gained considerable attention, mainly in connection with its applicability to non-classical models for materials. I introduce a geometrical approach to possibly infinite dimensional dynamical systems, based on the theory of Banach manifolds, which has not yet been fully exploited in Continuum Mechanics, though it has been used in some particular cases. This theory generalizes the Virtual Power framework, being even more flexible and allowing for the construction of continuum mechanical models on non-Euclidean domains. I studied the mathematical properties of a general linear isotropic incompressible second-gradient fluid. Constitutive prescriptions for these fluids are discussed, together with the constraints imposed by thermodynamical considerations. The key features of the analyzed model are the possibility of describing the adherence interaction of a three-dimensional fluid with one-dimensional structures immersed in it, and also of including concentrated interactions. A presentation of higher-gradient theories is provided, using the general framework proposed for dynamical systems. They turn out to be a particular class of continuum mechanical models, arising from precise assumptions on the kinematics of the descriptors of the system. Higher-order powers are defined as integral representations of elements of the cotangent bundle on the Banach manifold of the descriptors. Exploiting equivalent integral representations for powers of arbitrary order, the appearance of boundary interactions with a non-standard structure is described. The differential problems associated with the pressure-driven flow of a second-order linear liquid, which adheres to a one-dimensional structure, is considered. Existence and uniqueness of solution are established, also for the situation in which the one-dimensional structure drags the three-dimensional fluid, producing the motion. Finally, some examples are provided, in order to give explicit solutions, to show how the concentrated stresses, if present, can be computed, and to suggest possible interpretations for the physical meaning of the higher-order material parameters.

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Liebe, Tina. « Theory and numerics of higher gradient inelastic material behavior ». [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=967632153.

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Liebe, Tina [Verfasser]. « Theory and numerics of higher gradient inelastic material behavior / von Tina Liebe ». 2003. http://d-nb.info/967632153/34.

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Καρλής, Γεράσιμος. « BEM solutions for linear elastic and fracture mechanics problems with microstructural effects ». Thesis, 2009. http://nemertes.lis.upatras.gr/jspui/handle/10889/2236.

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During this thesis, a Boundary Element Method (BEM) has been developed for the solution of static linear elastic problems with microstructural effects in two (2D) and three dimensions (3D).The second simplified form of Mindlin's Generalized Gradient Elasticity Theory (Mindlin's Form II)has been employed. The fundamental solution of the 4th order partial differential equation, that describes the aforementioned theory, has been derived and the integral equations that govern Mindlin's Form II Gradient Elasticity Theory have been obtained. Furthermore, a BEM formulation has been developed and specific Boundary Value Problems (BVPs) were solved numerically and compared with the corresponding analytical solutions to verify the correctness of the formulation and demonstrate its accuracy. Moreover, two new partially discontinuous boundary elements with variable order of singularity, a line and a quadrilateral element, have been developed for the solution of fracture mechanics problems. The calculation of the unknown fields near the crack tip (or front) demanded the use of elements that could interpolate abruptly varying fields. The new elements were created in a way that their interpolation functions were no longer quadratic but their behavior depended on the order of singularity of each field. Finally, the Stress Intensity Factor (SIF) of the crack has been calculated with high accuracy, based on the element's nodal traction values. Static fracture mechanics problems for Mode I and Mixed Mode (I & II) cracks, have been solved in 2D and 3D and the corresponding SIFs have been obtained, in the context of both classical and Form II Gradient Elasticity theories.
Κατά τη διάρκεια της παρούσας διδακτορικής διατριβής, αναπτύχθηκε Μέθοδος Συνοριακών Στοιχείων (ΜΣΣ) για την επίλυση στατικών προβλημάτων ελαστικότητας με επιδράσεις μικροδομής σε δύο και τρεις διαστάσεις. Η θεωρία στην οποία εφαρμόστηκε η ΜΣΣ είναι η δεύτερη απλοποιημένη μορφή της γενικευμένης θεωρίας ελαστικότητας του Mindlin. Για τη συγκεκριμένη θεωρία ευρέθη η θεμελιώδης της μερικής διαφορικής εξίσωσης 4ης τάξης που περιγράφει τη συμπεριφορά των συγκεκριμένων υλικών και κατασκευών. Επίσης διατυπώθηκε η ολοκληρωτική εξίσωση των αντίστοιχων προβλημάτων και έγινε η αριθμητική εφαρμογή μέσω της ΜΣΣ. Επιλύθηκα αριθμητικά συγκεκριμένα προβλήματα συνοριακών τιμών και έγινε σύγκριση των αποτελεσμάτων με τα αντίστοιχα θεωρητικά. Στη συνέχεια αναπτύχθηκαν δύο νέα ασυνεχή στοιχεία μεταβλητής τάξης ιδιομορφίας με σκοπό την επίλυση προβλημάτων θραυστομηχανικής, ένα για δισδιάστατα και ένα για τρισδιάστατα προβλήματα. Συγκεκριμένα, επειδή τα πεδία των τάσεων απειρίζονται στην κορυφή μιας ρωγμής και περιέχουν συγκεκριμένων τύπων ιδιομορφίες δεν ήταν δυνατός ο ακριβής υπολογισμός των πεδίων αυτών κοντά στη ρωγμή με τα συνήθη τετραγωνικά συνοριακά στοιχεία. Ως εκ τούτου τα νέα στοιχεία κατασκευάστηκαν με τέτοιο τρόπο ώστε οι συναρτήσεις παρεμβολής τους να μην είναι τετραγωνικες, αλλά να εξαρτώνται από τον τύπο ιδιομορφίας του κάθε πεδίου. Έπειτα, έγινε ακριβής υπολογισμός του συντελεστή έντασης τάσης της ρωγμής με βάση τις τιμές του πεδίου των τάσεων κοντά σε αυτή. Τέλος επιλύθηκαν στατικά προβλήματα θραυστομηχανικής σε δύο και τρεις διαστάσεις και υπολογίστηκαν οι συντελεστές έντασης τάσης για ρωγμές σε υλικά με επίδραση μικροδομής.

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Chapitres de livres sur le sujet "Higher-gradient theorie"

dell’Isola, Francesco, Pierre Seppecher et Alessandro Della Corte. « Higher Gradient Theories and Their Foundations ». Dans Encyclopedia of Continuum Mechanics, 1–10. Berlin, Heidelberg : Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-53605-6_151-1.

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dell’Isola, Francesco, Pierre Seppecher et Alessandro Della Corte. « Higher Gradient Theories and Their Foundations ». Dans Encyclopedia of Continuum Mechanics, 1090–99. Berlin, Heidelberg : Springer Berlin Heidelberg, 2020. http://dx.doi.org/10.1007/978-3-662-55771-6_151.

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Müller, Wolfgang H. « The Experimental Evidence for Higher Gradient Theories ». Dans Mechanics of Strain Gradient Materials, 1–18. Cham : Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-43830-2_1.

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Lurie, Sergey, et Petr Belov. « From Generalized Theories of Media with Fields of Defects to Closed Variational Models of the Coupled Gradient Thermoelasticity and Thermal Conductivity ». Dans Higher Gradient Materials and Related Generalized Continua, 135–54. Cham : Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-30406-5_8.

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Maugin, Gérard A. « H–I : From “Higher-Order Gradient Theories” to “Ionic Crystals (Elasticity of)” ». Dans Advanced Structured Materials, 107–25. Singapore : Springer Singapore, 2016. http://dx.doi.org/10.1007/978-981-10-2434-4_9.

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N., Ehsan, Z. Jane et Rabab K. « Image Watermarking in Higher-Order Gradient Domain ». Dans Advances in Wavelet Theory and Their Applications in Engineering, Physics and Technology. InTech, 2012. http://dx.doi.org/10.5772/35603.

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Ryan, Kevin M. « Weight scales for stress ». Dans Prosodic Weight, 22–97. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198817949.003.0002.

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Stress placement in words is often affected by syllable weight, stress being attracted to heavy syllables. Weight in such cases is usually binary (heavy vs. light) but often instantiates more complex scales. This chapter focuses especially on the phonological analysis of ternary and higher order scales, featuring case studies of several languages set in Optimality Theory. It argues that such scales must be analyzed in terms of vowel prominence rather than moraic coercion or coda prominence. The relation of geminates to stress also features prominently, as it is maintained that geminates can be analyzed as uniformly moraic for stress. Finally, several cases of gradient weight for stress are surveyed, including English. In these systems, stress placement responds statistically to weight, which manifests a fine-grained continuum rather than a simple categorical opposition and often includes onset and sonority effects.

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Hoyt, Douglas V., et Kenneth H. Shatten. « Storms ». Dans The Role of the Sun in Climate Change. Oxford University Press, 1997. http://dx.doi.org/10.1093/oso/9780195094138.003.0011.

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We now examine some attempts to link storm numbers and storm track locations to solar activity. The number of both tropical cyclones and thunderstorms has increased and decreased with time and location as a function of solar activity. In fact, an early correlation between the number of Indian cyclones and solar activity proved so startling it caused an explosion of related research. In the previous century, tropical cyclones were called hurricanes or typhoons. Today tropical cyclones refer only to the weaker tropical storms with sustained winds above 31 miles per hour. Here, tropical cyclones refer to the stronger storms like those in the previous century. Anywhere from 1 to about 30 hurricane-strength storms can form each year. Among other factors, formation of these storms requires oceanic water temperatures above 26 °C (79 °F). William Gray at Colorado State University has successfully predicted the number of Atlantic Ocean hurricanes each year. This number is a function of the equatorial wind direction, the sea-level air pressure in the Caribbean, the strength of the westerly winds near the top of the lower troposphere, the presence or absence of an El Niño current, and, particularly, the amount of rainfall in the Sahel in Africa. Earlier we noted that increased solar activity produces a corresponding increase in rainfall in some regions. Figure 6.4 indicates that increased rainfall in the Sahel is expected, so based on this expectation and Gray’s theory, hurricanes should increase in number. Higher solar activity and a higher solar irradiance can also be expected to increase the tropical ocean temperatures by a few tenths of a degree. These increased water temperatures tend to increase both the number of tropical cyclones and their intensity. Figure 7.1 illustrates the number of Atlantic Ocean hurricanes observed between 1962 and 1994 as a function of the sea-surface temperatures (SST). A sharp gradient exists in the number of storms produced between 23 and 25 °C. In some regions, even a small increase in SST can lead to sharp increases in the number of tropical cyclones. Changes in solar brightness on the 11-year time scale could be expected to cause a corresponding cycle in the number and strength of tropical cyclones.

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Actes de conférences sur le sujet "Higher-gradient theorie"

Harlander, Robert Valentin. « The gradient flow at higher orders in perturbation theory ». Dans The 38th International Symposium on Lattice Field Theory. Trieste, Italy : Sissa Medialab, 2022. http://dx.doi.org/10.22323/1.396.0489.

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Pucha, Raghuram V., Gnyaneshwar Ramakrishna et Suresh K. Sitaraman. « Mechanics Issues at Micro-Scale Modeling of Electronic Packages ». Dans ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/epp-24709.

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Abstract Due to the temperature dependent material properties and low cycle thermo-mechanical fatigue of electronic packaging interconnects and components, plasticity theories are extensively used to understand their mechanical response in estimating the fatigue life. Experimental evidence indicates that plastic deformation at small scales depends not only on the state variables of stress and strain, but also on their higher order gradients. In this paper mechanics issues related to strain gradient plasticity at micron scale are reviewed through strain gradient enhanced continuum theories. A plastic strain gradient-based approach is employed to study the thermo-mechanical deformation of microvia structure.

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Muller, Wolfgang H., Kerstin Weinberg et Thomas Bohme. « A Higher Gradient Theory of Multiphase Solid Mixtures and its Application to Lead-Free Solder Micro-Morphology ». Dans 2007 9th Electronics Packaging Technology Conference. IEEE, 2007. http://dx.doi.org/10.1109/eptc.2007.4469733.

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Voyiadjis, George Z., et Robert J. Dorgan. « Formulation of a Gradient Enhanced Coupled Damage-Plasticity Model ». Dans ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-59890.

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An overview of the formulation of a gradient enhanced continuum coupled damage-plasticity model as a constitutive framework to model the nonlocal response of materials is presented. The formulation uses a thermodynamically consistent framework to introduce material length scales through the gradients of the hardening variables. The development of evolution equations for plasticity and damage is treated in a similar mathematical approach and formulation since both address defects such as dislocations for the former and cracks/voids for the later. The gradient enhancements are investigated as powerful tools for modeling observations at the microscale that are not possible to interpret with classical deformation models. By the introduction of higher order gradients, this model is able to predict the size of localized zones based on material constants, as opposed to local models where the loss of ellipticity causes the localized zones to be mesh dependent. Justification for the gradient theory is given by approximating nonlocal theory through a truncated Taylor expansion.

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Abu Al-Rub, Rashid K., et George Z. Voyiadjis. « Modeling the Size and Interface Effects in Thin Metal Film-Substrate Systems Using the Strain Gradient Plasticity ». Dans ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-42020.

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It is well-known by now through intensive experimental studies that have been performed at the micron and nano length scales that the material mechanical properties strongly depend on the size of specimen and the microstructural features. The classical continuum mechanics fails to address this problem since no material length scale exists in its constitutive description. On the other hand, nonlocal continuum theories of integral-type or gradient-type have been to a good extent successful in predicting this type of size effect. However, they fail to predict size effects when strain gradients are minimal such as the Hall-Petch effect. This problem is the main focus of this work. The effect of the material microstructural interfaces increase as the surface-to-volume ratio increases. It is shown in this work that interfacial effects have a profound impact on the scale-dependent plasticity encountered in micro/nano-systems. This is achieved by developing a higher-order gradient-dependent plasticity theory that enforces microscopic boundary conditions at interfaces and free surfaces. These nonstandard boundary conditions relate the microtraction stress at the interface to the interfacial energy. Application of the proposed framework to size effects in shear loading of a thin-film on an elastic substrate is presented. Three film-interface conditions are modeled: soft, intermediate, and hard interfaces.

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Shankaran, Sriram, et Andre Marta. « Robust Optimization for Aerodynamic Problems Using Polynomial Chaos and Adjoints ». Dans ASME Turbo Expo 2012 : Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gt2012-69580.

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The central theme of this paper is to show how one can combine Polynomial Chaos Expansions (PCE) and adjoint theory to efficiently obtain sensitivities for robust optimal control and optimization. Two different formulations to obtain the sensitivities are presented: 1) Semi-intrusive: builds an adjoint equation for each PCE mode and and uses the combination of the gradient for each basis-adjoint pair to form the overall gradient, 2) Non-intrusive: solves an adjoint solution for each sample point to form a PCE for the gradient. The latter is used to obtain all the results in the paper. However, the two methods are compared to show that the latter involves an approximation which can lead to different solutions depending on the magnitude of the higher-order modes. The resulting gradient is then used in an iterative optimization procedure. Using an analytical problem to determine the trade-off between cost and accuracy of some PCE methods, the optimization algorithm is applied to an airfoil and turbine vane optimization problem. The robust optimal solutions for the airfoil optimization problem are compared against a multi-point design approach and shown to result in better designs in the constrained (not included here) and unconstrained case. In the turbine vane case, the mean loss is reduced by close to 4 tenths of a point.

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Duan, Wenguang, Baojiang Sun, Deng Pan, Jianchun Xu et Jian Liu. « Recent Advances in Supercritical CO2 Fracturing : New Theory, New Technology, and Application ». Dans SPE Middle East Oil & Gas Show and Conference. SPE, 2021. http://dx.doi.org/10.2118/204725-ms.

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Abstract The shale oil reservoir in Jimusaer has the characteristics of low porosity and low permeability, resulting in significant resistance in oil flow compared with conventional oil reservoirs. Fracturing is needed to increase shale oil production. Supercritical CO2 (SC-CO2) is an ideal choice for fracturing fluid due to its unique physical and chemical properties. SC-CO2 fracturing is able to make CO2 flow into microfractures and greatly reduce the pumping pressure. New progress has been made in the application of the supercritical CO2 fracturing technology in Jimusaer. A phase control model of SC-CO2 fracturing as a function of temperature and pressure is established, which takes into account the SC-CO2 features, intrinsic energy, flow behavior in fracture and fluid filtration. In this paper, the influences of injection pressure and temperature, injection rate, temperature-pressure field, temperature gradient, and phase behavior are analyzed extensively, in addition, the phase control model and its chart of fracture are presented. The proppant accumulation height reduces by a small amount with the increase of the fracturing fluid injection rate. It is necessary to improve the proppant pumping technology by the sand embankment section and proppant concentration. The liquid transforms into supercritical fluid, when flowing in wellbores and fractures. Different fractures have different phase points, and a lower injection temperature is affected by higher injection rate, lower temperature gradient and closer position from transformation point to the end of fracture. Therefore, in order to achieve a better fracturing effect, the injection temperature, pressure, and rate need to be optimized by surface equipment according to the reservoir conditions, to control the phase behavior of CO2. We built a phase control model for the SC-CO2 fracturing technology, which considers temperature control. We also developed some new techniques to improve SC-CO2 fracturing which is critically needed in the Jimusaer oilfield.

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Xing, Baihui, Jing Wang, Haotian Wei, Juan Shang, Zhengli Hua, Chaohua Gu et Jinyang Zheng. « Difference of Hydrogen Diffusion Regularity Between Interstice-Doped and Substitution-Doped Formed by Steel Carburizing ». Dans ASME 2022 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/pvp2022-84462.

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Abstract Carburizing treatment can improve the carbon content of the workpiece material, and obtain higher contact fatigue strength, bending fatigue strength, as well as higher surface hardness. After carburizing, the existence of carbon atoms can hinder the adsorption and diffusion of hydrogen, thus reducing the hydrogen embrittlement. First-principles plane wave calculations based on spin-polarized density-functional theory (DFT) and the generalized gradient approximation (GGA) have been used to study the adsorption and permeation of hydrogen on iron in the bulk with carbon interstice solid solution and carbon substitution solid solution. Considering that hydrogen diffusion is faster in martensitic tissue, bcc-Fe structure is selected for the model. The results show that the hydrogen diffusion rate Di in the interstice solid solution is higher than Ds in the substitution solid solution. The formation of substitution solid solution is promoted by more vacancies in the lattice. When the vacancy is occupied by carbon atoms, the hydrogen diffusion rate is reduced. This phenomenon is more obvious for Fe48C16 structure with higher carbon ratio. Besides, charge density diagram and state density analysis are also consistent with this conclusion. Therefore, during carburizing, Increasing the content of carbon and carbon substituted solid solution can reduce the penetration of hydrogen in the material.

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Bake, Friedrich, Ulf Michel et Ingo Roehle. « Investigation of Entropy Noise in Aero-Engine Combustors ». Dans ASME Turbo Expo 2006 : Power for Land, Sea, and Air. ASMEDC, 2006. http://dx.doi.org/10.1115/gt2006-90093.

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Strong evidence is presented that entropy noise is the major source of external noise in aero-engine combustion. Entropy noise is generated in the outlet nozzles of combustors. Low frequency entropy noise — which was predicted earlier in theory and numerical simulations — was successfully detected in a generic aero-engine combustion chamber. It is shown that entropy noise dominates even in the case of thermo-acoustic resonances. In addition to this, a different noise generating mechanism was discovered that is presumably of even higher relevance to jet engines: There is strong evidence of broad band entropy noise at higher frequencies (1 kHz to 3 kHz in the reported tests). This unexpected effect can be explained by the interaction of small scale entropy perturbations (hot spots) with the strong pressure gradient in the outlet nozzle. The direct combustion noise of the flame zone seems to be of minor importance for the noise emission to the ambiance. The combustion experiments were supplemented by experiments with electrical heating. Two different methods for generating entropy waves were used, a pulse excitation and a sinusoidal excitation. In addition, high-frequency entropy noise was generated by steady electrical heating.

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Botros, K. K., Lorne Carlson, Brian Rothwell et Philip Venton. « Semi-Empirical Correlation to Quantify the Effects of Pipe Diameter and Internal Surface Roughness on the Decompression Wave Speed in Natural Gas Mixtures ». Dans 2012 9th International Pipeline Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ipc2012-90050.

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GASDECOM is typically used in the design of gas pipelines for calculating decompression speed in connection with the Battelle two-curve method used throughout the pipeline industry for the control of propagating ductile fracture. GASDECOM idealizes the decompression process as isentropic and one-dimensional, taking no account of pipe wall frictional effects. Previous shock tube tests showed that decompression wave speeds in smaller diameter and rough pipes are consistently slower than those predicted by GASDECOM for the same conditions of mixture composition and initial pressure and temperature. Preliminary analysis based on perturbation theory and the fundamental momentum equation showed a correction term to be subtracted from the ‘ideal’ value of the decompression speed. One parameter in this correction term involves a dynamic spatial pressure gradient of the outflow at the rupture location. While this is difficult to obtain without a shock tube or actual rupture test, data from 14 shock tube tests, as well as from 14 full scale burst tests involving a variety of gas mixture compositions, were analyzed to quantify the variation of this pressure gradient with gas conditions and outflow Mach number. A semi-empirical relationship was found to correlate this pressure gradient parameter with two basic parameters representing the natural gas mixture, namely the molecular weight of the mixture and its higher heating value (HHV). For lean gas mixes, the semi-empirically obtained correlation was found to fit very well the experimentally determined decompression wave speed curve. For rich gas mixes, the correlation fits both branches of the curve; above and below the plateau pressure. This paper provides the basis for the derived semi-empirical correlation, and suggests a procedure (with examples) to correct the ‘ideal’ (frictionless) GASDECOM prediction to account for both the effects of pipe diameter and pipe internal wall surface roughness.

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