The Experts below are selected from a list of 150 Experts worldwide ranked by ideXlab platform
A R Azami - One of the best experts on this subject based on the ideXlab platform.
-
Reproducing Kernel Particle Method in Plasticity of Pressure-Sensitive Material with Reference to Powder Forming Process
Computational Mechanics, 2007Co-Authors: Amir R. Khoei, M. Samimi, A R AzamiAbstract:In this paper, an application of the reproducing kernel particle method (RKPM) is presented in plasticity behavior of pressure-sensitive material. The RKPM technique is implemented in large deformation analysis of powder compaction process. The RKPM shape function and its derivatives are constructed by imposing the consistency conditions. The essential boundary conditions are enforced by the use of the penalty approach. The support of the RKPM shape function covers the same set of particles during powder compaction, hence no instability is encountered in the large deformation computation. A double-surface plasticity model is developed in numerical simulation of pressure-sensitive material. The plasticity model includes a failure surface and an elliptical cap, which closes the open space between the failure surface and Hydrostatic Axis. The moving cap expands in the stress space according to a specified hardening rule. The cap model is presented within the framework of large deformation RKPM analysis in order to predict the non-uniform relative density distribution during powder die pressing. Numerical computations are performed to demonstrate the applicability of the algorithm in modeling of powder forming processes and the results are compared to those obtained from finite element simulation to demonstrate the accuracy of the proposed model.
-
extended finite element method in plasticity forming of powder compaction with contact friction
International Journal of Solids and Structures, 2006Co-Authors: Amir R. Khoei, Amir Shamloo, A R AzamiAbstract:In this paper, a new computational technique is presented based on the eXtended Finite Element Method (X-FEM) in pressure-sensitive plasticity of powder compaction considering frictional contact. In X-FEM, the need for mesh adaption to discontinuity interface is neglected and the process is accomplished by partitioning the domain with some triangular sub-elements whose Gauss points are used for integration of the domain of the elements. The technique is applied by employing additional functions, which are added to approximate the displacement field of the elements located on the interface. The double-surface cap plasticity model is employed within the X-FEM framework in numerical simulation of powder material. The plasticity model includes a failure surface and an elliptical cap, which closes the open space between the failure surface and Hydrostatic Axis. The moving cap expands in the stress space according to a specified hardening rule. The frictional behavior of contact between two bodies is modeled by using the X-FEM technique and applying the Heaviside enrichment function. The application of X-FEM technique in simulation of pressure-sensitive material is presented in an incremental manner and the role of sub-elements in simulation of contact treatment is demonstrated. Finally, several numerical examples are analyzed with special reference to plasticity forming of powder compaction.
-
Modeling of pressure-sensitive materials using a cap plasticity theory in extended finite element method
Journal of Materials Processing Technology, 2005Co-Authors: Amir Shamloo, A R Azami, Amir R. KhoeiAbstract:Abstract In this paper, a new computational technique based on the extended finite element method (X-FEM) is presented in elasto-plastic behavior of pressure-sensitive material. The cap plasticity model is employed within the X-FEM framework in numerical simulation of powder die pressing. The double-surface plasticity model includes a failure surface and an elliptical yield cap, which closes the open space between the failure surface and Hydrostatic Axis. The yield cap expands in the stress space according to a specified hardening rule. Application of the X-FEM in simulation of two phase plasticity continuums is presented in an incremental manner and the role of sub-elements in the partition of unity method is demonstrated. Finally, three numerical examples, including: a plate with hole subjected to compression, a double-layer foundation and the compaction simulation of metal powder are analyzed numerically.
Amir R. Khoei - One of the best experts on this subject based on the ideXlab platform.
-
Reproducing Kernel Particle Method in Plasticity of Pressure-Sensitive Material with Reference to Powder Forming Process
Computational Mechanics, 2007Co-Authors: Amir R. Khoei, M. Samimi, A R AzamiAbstract:In this paper, an application of the reproducing kernel particle method (RKPM) is presented in plasticity behavior of pressure-sensitive material. The RKPM technique is implemented in large deformation analysis of powder compaction process. The RKPM shape function and its derivatives are constructed by imposing the consistency conditions. The essential boundary conditions are enforced by the use of the penalty approach. The support of the RKPM shape function covers the same set of particles during powder compaction, hence no instability is encountered in the large deformation computation. A double-surface plasticity model is developed in numerical simulation of pressure-sensitive material. The plasticity model includes a failure surface and an elliptical cap, which closes the open space between the failure surface and Hydrostatic Axis. The moving cap expands in the stress space according to a specified hardening rule. The cap model is presented within the framework of large deformation RKPM analysis in order to predict the non-uniform relative density distribution during powder die pressing. Numerical computations are performed to demonstrate the applicability of the algorithm in modeling of powder forming processes and the results are compared to those obtained from finite element simulation to demonstrate the accuracy of the proposed model.
-
extended finite element method in plasticity forming of powder compaction with contact friction
International Journal of Solids and Structures, 2006Co-Authors: Amir R. Khoei, Amir Shamloo, A R AzamiAbstract:In this paper, a new computational technique is presented based on the eXtended Finite Element Method (X-FEM) in pressure-sensitive plasticity of powder compaction considering frictional contact. In X-FEM, the need for mesh adaption to discontinuity interface is neglected and the process is accomplished by partitioning the domain with some triangular sub-elements whose Gauss points are used for integration of the domain of the elements. The technique is applied by employing additional functions, which are added to approximate the displacement field of the elements located on the interface. The double-surface cap plasticity model is employed within the X-FEM framework in numerical simulation of powder material. The plasticity model includes a failure surface and an elliptical cap, which closes the open space between the failure surface and Hydrostatic Axis. The moving cap expands in the stress space according to a specified hardening rule. The frictional behavior of contact between two bodies is modeled by using the X-FEM technique and applying the Heaviside enrichment function. The application of X-FEM technique in simulation of pressure-sensitive material is presented in an incremental manner and the role of sub-elements in simulation of contact treatment is demonstrated. Finally, several numerical examples are analyzed with special reference to plasticity forming of powder compaction.
-
The extended finite element method (X-FEM) for powder forming problems
Journal of Materials Processing Technology, 2006Co-Authors: Amir R. Khoei, Amir Shamloo, M. Anahid, K. ShahimAbstract:Abstract In this paper, the eXtended Finite Element Method (X-FEM) is developed in pressure-sensitive plasticity of powder compaction process. In X-FEM, the need for mesh adaption to discontinuity interface is neglected and the process is accomplished by employing additional functions, which are added to approximate the displacement field of the elements located on the interface. The double-surface cap plasticity model is employed within the X-FEM framework in numerical simulation of powder material. The plasticity model includes a failure surface and an elliptical cap, which closes the open space between the failure surface and Hydrostatic Axis. The moving cap expands in the stress space according to a specified hardening rule. The application of X-FEM technique in simulation of powder material is presented in an incremental manner. Finally, the numerical example of a shaped tablet component is analyzed numerically.
-
Modeling of pressure-sensitive materials using a cap plasticity theory in extended finite element method
Journal of Materials Processing Technology, 2005Co-Authors: Amir Shamloo, A R Azami, Amir R. KhoeiAbstract:Abstract In this paper, a new computational technique based on the extended finite element method (X-FEM) is presented in elasto-plastic behavior of pressure-sensitive material. The cap plasticity model is employed within the X-FEM framework in numerical simulation of powder die pressing. The double-surface plasticity model includes a failure surface and an elliptical yield cap, which closes the open space between the failure surface and Hydrostatic Axis. The yield cap expands in the stress space according to a specified hardening rule. Application of the X-FEM in simulation of two phase plasticity continuums is presented in an incremental manner and the role of sub-elements in the partition of unity method is demonstrated. Finally, three numerical examples, including: a plate with hole subjected to compression, a double-layer foundation and the compaction simulation of metal powder are analyzed numerically.
Pericles S. Theocaris - One of the best experts on this subject based on the ideXlab platform.
-
Weighing Failure Tensor Polynomial Criteria for Composites
International Journal of Damage Mechanics, 1992Co-Authors: Pericles S. TheocarisAbstract:Several interesting versions of the tensor polynomial failure criterion for composites were compared with the family of the elliptic paraboloid failure criteria (EPFS), with symmetry axes parallel to the Hydrostatic Axis. A critical appraisal of the most important theories was presented and a comparison was made with existing experi- mental data in triaxial stress states. The superiority of the EPFS over any other criterion was established. Furthermore, the more flexible ellipsoid failure surface criterion, an ex- tension of EPFS, may be used for special types of material such as foams, porous material and other materials that fail under internal buckling in general compression.
-
Positive and negative failure-shears in orthotropic materials
Journal of Reinforced Plastics and Composites, 1992Co-Authors: Pericles S. TheocarisAbstract:Failure predictions of off-Axis loaded fiber composite laminae are given according to the elliptic paraboloid failure criterion for anisotropic solids [1]. The failure condition assumes that for any anisotropic solid a safe triaxial loading path exists, along the Hydrostatic compression, and thus the failure surface must be open-ended. By appropriately formulating the failure criterion, it is shown that the geometric interpretation of the failure surface in the principal stress space is an elliptic paraboloid (EPFS) whose Axis of symmetry is parallel to the Hydrostatic Axis in the principal stress space. Because of the shape and position of the EPFS, the intersections by principal stress planes corresponding to loadings of off-Axis laminae of a fiber composite are represented by ellipses whose origins are displaced from the origin of the stress reference frame. This fact creates unequal shear yield stresses in the positive and negative sense clearly manifested in a pure shear failure loading.The predictio...
-
The symmetric ellipsoid failure surface for the transversely isotropic body
Acta Mechanica, 1992Co-Authors: Pericles S. TheocarisAbstract:A realistic criterion in the 3D-principal stress space for describing failure of transversely isotropic bodies taking also into account the strength differential effect was shown to be the elliptic paraboloid failure surface (EPFS) [5]. The criterion, however, stipulates that in the compression-compression-compression octant these materials may sustain very high loadings. In order to remedy this ambiguous definition of failure in this zone for the compression strong materials or in the domain of the tension-tension octant for the tension strog materials an improved version of the EPFS was introduced in this paper. Based on the same principles as the EPFS a symmetric ellipsoid failure surface is defined whose symmetry Axis is parallel to the Hydrostatic Axis, which is also passing through the three pairs of failure strengths in tension and compression along each of the principal stress axes.
-
Tensor failure criteria for composites: Properties and comparison of the ellipsoid failure surfaces with experiments
Advances in Polymer Technology, 1991Co-Authors: Pericles S. TheocarisAbstract:A realistic criterion was introduced in the 3D principal stress space for describing failure of transversely isotropic bodies taking also into account the strength differential effect. This criterion is represented by an elliptic paraboloid failure surface (EPFS). The criterion stipulates that in the compression–compression–compression octant these materials may sustain very high loadings. To remedy this ambiguous definition of failure in this zone, an improved version of the EPFS was also introduced as a complement of the EPFS criterion. Based on the same principles as the EPFS, a symmetric ellipsoid failure surface is defined whose symmetry Axis is parallel to the Hydrostatic Axis, which is also passing though the three pairs of failure strengths in tension and compression along each of the principal stress axes. Both criteria are completely defined by stipulating that their symmetry axes are parallel to the Hydrostatic Axis and that the fourth rank tensors H defining failure should have a zero eigenvalue associated with the spherical tensor 1. Extensive experimental evidence with different orthotropic materials has shown that their failure results corroborate both criteria, depending on the form of their structure.
P. S. Theocaris - One of the best experts on this subject based on the ideXlab platform.
-
The symmetric ellipsoid failure surface for the transversely isotropic body
Acta Mechanica, 1992Co-Authors: P. S. TheocarisAbstract:A realistic criterion in the 3D-principal stress space for describing failure of transversely isotropic bodies taking also into account the strength differential effect was shown to be the elliptic paraboloid failure surface (EPFS) [5]. The criterion, however, stipulates that in the compression-compression-compression octant these materials may sustain very high loadings. In order to remedy this ambiguous definition of failure in this zone for the compression strong materials or in the domain of the tension-tension octant for the tension strog materials an improved version of the EPFS was introduced in this paper. Based on the same principles as the EPFS a symmetric ellipsoid failure surface is defined whose symmetry Axis is parallel to the Hydrostatic Axis, which is also passing through the three pairs of failure strengths in tension and compression along each of the principal stress axes. Since the symmetric ellipsoid failure criterion is a versatile one, based on the same hypotheses derived from assertions and long experrimental evidence as the EPFS, thus succeding to interrelate failure with the basic concepts and principles of mechanics, it constitutes a powerful and reliable general type of criterion. It was shown that extensive experimental evidence corroborates the results derived from this criterion along the basic intersections of this failure surface.
-
Properties and experimental verification of the paraboloid failure criterion with transversely isotropic materials
Journal of Materials Science, 1990Co-Authors: P. S. TheocarisAbstract:A suitable criterion for describing the yielding and failure behaviour of transversely isotropic materials in the three-dimensional principal stress space, taking into account the strength differential effects of the material, has been recently established by representing this failure locus by an elliptic paraboloid surface, which has an Axis of symmetry that remains parallel to the Hydrostatic Axis and lies on the principal diagonal plane containing the strongest strength Axis ( σ _3). The properties of the elliptic paraboloid surface have already been established for the general anisotropic body and its validity was tested by checking it with existing experimental results and comparing it with similar criteria. In this paper the elliptic paraboloid failure criterion was tested with typical fibre composites and other transversely isotropic materials in order to prove further its soundness and, moreover, to disclose the intimate connection between strength differential parameters and the coefficients of anisotropy of the material, and their influence on the size, position, form and orientation of the failure locus.
Poul V. Lade - One of the best experts on this subject based on the ideXlab platform.
-
Estimating Parameters from a Single Test for the Three-Dimensional Failure Criterion for Frictional Materials
Journal of Geotechnical and Geoenvironmental Engineering, 2014Co-Authors: Poul V. LadeAbstract:AbstractThe three-dimensional failure criterion for soils was expanded to include concrete and used for rocks. The failure criterion is expressed in terms of the first and the third invariants of the stress tensor and it requires two parameters for characterization of the strength of soils and three parameters for concrete and rocks. For soils, one parameter is used to describe the opening angle of the failure surface, i.e., similar to the friction angle, and the second parameter is employed to describe the curvature of the failure surface in meridian planes that contain the Hydrostatic Axis. The third parameter, used for concrete and rocks, is slightly higher than the uniaxial tensile strength and is used to capture the cohesion and tensile strength. Typically, the results of three triaxial compression tests and the tensile strength from a Brazilian test or from an estimate are required for the determination of these three parameters. Careful inspection of parameters, determined from numerous high-qualit...
-
CHARACTERIZATION OF CROSS-ANISOTROPIC SOIL DEPOSITS FROM ISOTROPIC COMPRESSION TESTS
Soils and Foundations, 2005Co-Authors: Poul V. Lade, Andrei V. AbelevAbstract:Isotropic compression tests have been performed on two fine sands. Specimens of Nevada sand were prepared by air pluviation and by funnel deposition followed by tapping to relative densities of 30, 50, 70, and 90%. Specimens of Santa Monica Beach sand were prepared by air pluviation to a relative density of 90%. All specimens exhibited cross-anisotropic behavior, both in terms of total strains and in terms of unloading strains. Small pressure cycles performed during loading and unloading were used to study elastic behavior. The inclination angles of the total and plastic strain increment vectors relative to the Hydrostatic Axis in the principal stress space were used to express and to study the evolution of cross-anisotropy in the sand deposits. In the context of elasto-plastic constitutive modeling, the variation of the inclination of the plastic strain increment vector was further characterized by a rotation of the plastic potential surface as a means to capture the inherent cross-anisotropic behavior observed in such sand deposits.
-
Initiation of static instability in the submarine Nerlerk berm
Canadian Geotechnical Journal, 1993Co-Authors: Poul V. LadeAbstract:According to stability postulates by other authors, soils that exhibit nonassociated flow may become unstable when exposed to certain stress paths inside the failure surface. Several series of conventional triaxial tests on fully saturated specimens have been performed to study the regions of stable and unstable behavior. For saturated specimens that tend to compress, undrained conditions lead to effective stress paths directed within the region of potential instability, and instability is observed, provided the yield surface opens up in the outward direction of the Hydrostatic Axis. Thus, instability occurs inside the failure surface. Instability is not synonymous with failure, although both lead to catastrophic events. The location of the region of potential instability and its determination are discussed. The submarine Nerlerk berm, which suffered six slides during its construction, is analyzed using a newly developed method of instability analysis. It is shown that conventional slope stability methods...
-
Static Instability and Liquefaction of Loose Fine Sandy Slopes
Journal of Geotechnical Engineering, 1992Co-Authors: Poul V. LadeAbstract:Soils that exhibit nonassociated flow may, according to stability postulates by Drucker and by Hill, become unstable when exposed to certain stress paths inside the failure surface. Series of conventional triaxial tests on fully saturated and on partly saturated specimens were performed under drained and undrained conditions to study the regions of stable and unstable behavior. For specimens that compress and have degrees of saturation higher than critical, undrained conditions lead to effective stress paths directed within the region of potential instability, and instability was observed provided the yield surface opens up in the outward direction of the Hydrostatic Axis. Thus, instability occurs inside the failure surface. Instability is not synonymous with failure, although both may lead to catastrophic events. The location of the instability line is discussed. Examples of a shallow submarine slope and a nearly fully saturated steeper slope representing a tailings dam, which both should remain stable a...
-
Instability and Plastic Flow of Soils. II: Analytical Investigation
Journal of Engineering Mechanics-asce, 1990Co-Authors: Daniel Pradel, Poul V. LadeAbstract:Based on the condition that a stable material is able to sustain a small perturbation in load, the stability of an elasto‐plastic granular material with non‐associated flow is analyzed, and necessary conditions for mechanical stability of saturated and partly saturated specimens are proposed. Using experimental data obtained from drained tests, the local yield and plastic potential surfaces are established. Their position shows the existence of a wedge where plastic loading occurs, while the second increment of plastic work is negative. Under drained conditions where strains are free to develop without restraint, instabilities cannot develop, and the material will be stable, even when Drucker's postulate is violated. For an elasto‐plastic material under undrained conditions with full or partial saturation, the proposed conditions show that instability may occur when the yield surface opens in the outward direction of the Hydrostatic Axis, and the material tends to compress. The experimental data supported...
