The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
M Ortiz - One of the best experts on this subject based on the ideXlab platform.
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variational h adaption in finite deformation elasticity and Plasticity
International Journal for Numerical Methods in Engineering, 2007Co-Authors: Jorn Mosler, M OrtizAbstract:We ropose a variational h-adaption strategy in which the evolution of the mesh is driven directly by the governing minimum principle. This minimum principle is the principle of minimum potential energy in the case of elastostatics; and a minimum principle for the incremental static problem of elasto-viscoPlasticity. In particular, the mesh is refined locally when the resulting energy or incremental pseudo-energy released exceeds a certain threshold value. In order to avoid global recomputes, we estimate the local energy released by mesh refinement by means of a lower bound obtained by relaxing a local patch of elements. This bound can be computed locally, which reduces the complexity of the refinement algorithm to O(N). We also demonstrate how variational h-refinement can be combined with variational r-refinement to obtain a variational hr-refinement algorithm. Because of the strict variational nature of the h-refinement algorithm, the resulting meshes are anisotropic and outperform other refinement strategies based on aspect ratio or other purely geometrical measures of mesh quality. The versatility and rate of convergence of the resulting approach are illustrated by means of selected numerical examples. Copyright © 2007 John Wiley & Sons, Ltd.
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dislocation microstructures and the effective behavior of single crystals
Archive for Rational Mechanics and Analysis, 2005Co-Authors: Sergio Conti, M OrtizAbstract:We consider single-crystal Plasticity in the limiting case of infinite latent hardening, which signifies that the crystal must deform in single slip at all material points. This requirement introduces a nonconvex constraint, and thereby induces the formation of fine-scale structures. We restrict attention throughout to linearized kinematics and deformation theory of Plasticity, which is appropriate for monotonic proportional loading and confers the boundary value problem of Plasticity a well-defined variational structure analogous to elasticity. We first study a scale-invariant (local) problem. We show that, by developing microstructures in the form of sequential laminates of finite depth, crystals can beat the single-slip constraint, i.e., the macroscopic (relaxed) constitutive behavior is indistinguishable from multislip ideal Plasticity. In a second step, we include dislocation line energies, and hence a length scale, into the model. Different regimes lead to several possible types of microstructure patterns. We present constructions which achieve the various optimal scaling laws, and discuss the relation with experimentally known scalings, such as the Hall-Petch law.
Jn Reddy - One of the best experts on this subject based on the ideXlab platform.
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buckling analysis of elastic plastic nanoplates resting on a winkler pasternak foundation based on nonlocal third order plate theory
International Journal of Non-linear Mechanics, 2020Co-Authors: E Ruocco, Jn ReddyAbstract:Abstract The paper analyzes the elastic–plastic buckling behavior of thick, rectangular nanoplates embedded in a Winkler–Pasternak foundation, adopting the Reddy third-order plate theory in nonlocal elasticity. Elasto-Plasticity is accounted for by considering two alternative Plasticity theories, namely the J 2 flow incremental and the J 2 deformation theory, with material properties defined by a Ramberg–Osgood relation. An iterative procedure is proposed to obtain the critical load, and the corresponding critical mode, of plates simply supported on two opposite edges under applied uniaxial and biaxial loading conditions. Extensive analysis investigates the effects of geometrical, constitutive, and nonlocal parameters on the critical behavior of plates with different boundary conditions. To the best of the authors’ knowledge, there are no findings about elastoplastic buckling of nanoplates in the existing literature. It is therefore hoped that the results obtained may provide a helpful basis for comparison for future investigations.
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Buckling analysis of elastic–plastic nanoplates resting on a Winkler–Pasternak foundation based on nonlocal third-order plate theory
2020Co-Authors: Ruocco E, Jn ReddyAbstract:The paper analyzes the elastic–plastic buckling behavior of thick, rectangular nanoplates embedded in a Winkler–Pasternak foundation, adopting the Reddy third-order plate theory in nonlocal elasticity. Elasto-Plasticity is accounted for by considering two alternative Plasticity theories, namely the J2 flow incremental and the J2 deformation theory, with material properties defined by a Ramberg–Osgood relation. An iterative procedure is proposed to obtain the critical load, and the corresponding critical mode, of plates simply supported on two opposite edges under applied uniaxial and biaxial loading conditions. Extensive analysis investigates the effects of geometrical, constitutive, and nonlocal parameters on the critical behavior of plates with different boundary conditions. To the best of the authors’ knowledge, there are no findings about elastoplastic buckling of nanoplates in the existing literature. It is therefore hoped that the results obtained may provide a helpful basis for comparison for future investigations
Leone Corradi - One of the best experts on this subject based on the ideXlab platform.
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variational formulations for the plane strain elastic plastic problem for materials governed by the von mises criterion
International Journal of Plasticity, 1996Co-Authors: Antonio Capsoni, Leone CorradiAbstract:Path-dependent materials, complying with Drucker's postulate requirements and governed by an internal variable rate Plasticity model, are considered. A variational principle for the small strain, rate Plasticity problem is established in this context and extended to cover finite loading steps. Results are subsequently specialized to plane strain solids made of elastically isotropic materials with a plastic behavior governed by the von Mises criterion, accounting for combined isotropic and kinematic hardening. By exploiting previous results, the formulation is fully reduced to the plane. Further generalizations of the statements are also provided, which can be regarded as extensions to the elastic-plastic, plane strain problem of the Hu-Washizu principle in elasticity.
Katharina M Pickerfreyer - One of the best experts on this subject based on the ideXlab platform.
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tableting and tablet properties of alginates characterisation and potential for soft tableting
European Journal of Pharmaceutics and Biopharmaceutics, 2009Co-Authors: Wolfgang Schmid, Katharina M PickerfreyerAbstract:The aim of the study was to evaluate the suitability of alginates for Soft Tableting. For this purpose the compaction properties of alginates, varying in molecular weight, guluronic acid/mannuronic acid ratio and salt, were investigated and compared to MCC. Based on the mechanical properties, the suitability of the tested excipients for Soft Tableting was predicted. In order to test the prediction the tested materials were used to tablet enteric coated pellets, which served as a pressure sensitive material. The tableting behaviour was analysed by the 3-D modeling technique. The tablet properties were analysed by determining the elastic recovery and the compactibility. Alginates in general deformed elastically. The compression behaviour depended on the chemical composition of the alginates with sodium alginates being more elastic than potassium alginates. Tablets containing alginates with low guluronic acid content exhibited higher elasticity than tablets with alginates having a low mannuronic acid content. The Plasticity of potassium alginates was higher than for sodium alginates. However, the Plasticity of all tested alginates was lower than the Plasticity of MCC. The compactibility of the tested alginates was sufficient. The proposed prediction, which states that tableting excipients with higher elasticity are more suitable for tableting sensitive materials than plastic excipients, was valid for the tested materials. The elastic alginates inflicted less damage on the pellets than the plastic MCC. Thus, all alginates were more appropriate for tableting pressure sensitive materials than MCC.
Sayantan Chattoraj - One of the best experts on this subject based on the ideXlab platform.
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understanding the relationship between crystal structure Plasticity and compaction behaviour of theophylline methyl gallate and their 1 1 co crystal
CrystEngComm, 2010Co-Authors: Sayantan ChattorajAbstract:Theophylline and methyl gallate can form a 1 : 1 co-crystal. Their tableting performance follows the order of theophylline > co-crystal ≫ methyl gallate. While co-crystallization profoundly improves the tabletability of methyl gallate, it significantly deteriorates that of theophylline. This difference in bulk compaction behaviour originates from the dissimilar crystal Plasticity and elasticity, which results from unique molecular packing features in the respective crystal lattices. The presence of a three-dimensional hydrogen bonded network gives rise to very low Plasticity in the methyl gallate crystal, which leads to its poor tabletability. In contrast, the layers of two-dimensional rigid, hydrogen bonded molecules in the co-crystal improve the crystal Plasticity, by facilitating slip with shear that, in turn, enhances tabletability. However, theophylline undergoes plastic deformation more readily when compared to the co-crystal, because the slip layers in theophylline are composed of hydrogen bonded columns, which provide additional flexibility for slip. As a consequence, theophylline crystals have significantly enhanced tabletability.
