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Deformation Modes (deformation + mode)
Selected AbstractsBoundary characteristics in Heavily Deformed Metals,ADVANCED ENGINEERING MATERIALS, Issue 5 2003G. Winther Abstract The potential of creating nanostructured metals by plastic deformation to very high strains is currently the subject of intensive research. An important part of this research concerns evolution of the characteristics of deformation induced boundaries, in particular boundary spacing and boundary misorientation. The aim of this paper is to give an overview of the present understanding of the relations between these characteristics, the microscopic deformation mechanisms and the macroscopic deformation mode. [source] The stress,life fatigue behaviour of aluminium alloy foamsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2000McCullough The tension,tension and compression,compression nominal stress versus fatigue life responses of Alulight closed cell aluminium alloy foams have been measured for the compositions Al,1Mg,0.6Si and Al,1Mg,10Si (wt %), and for relative densities in the range 0.1,0.4. The fatigue strength of each foam increases with the relative density and with the mean applied stress, and is greater for the transverse orientation than for the longitudinal orientation. Under both tension,tension and compression,compression loading the dominant cyclic deformation mode appears to be material ratchetting; consequently, the fatigue life is highly sensitive to the magnitude of the applied stress. A micromechanical model is given to predict the dependence of life upon stress level and relative density. Panels containing a central hole were found to be notch insensitive for both tension,tension and compression,compression fatigue loading: the net-section strength equals the unnotched strength. [source] Mechanics of land subsidence due to groundwater pumpingINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2010Muniram Budhu Abstract This paper presents the formulation of the basic mechanics governing the changes in stress states from groundwater pumping and comparisons among predicted land subsidence from this mechanics with existing analyses and field data. Land subsidence is a growing, global problem caused by petroleum and groundwater withdrawal, mining operations, natural settlement, hydro-compaction, settlement of collapsible soils, settlement of organic soils and sinkholes. This paper is concerned with the land subsidence due to groundwater level decline by groundwater pumping. It is shown that the stress state consists of asymmetric stresses that are best simulated by a Cosserat rather than a Cauchy continuum. Land subsidence from groundwater level decline consists of vertical compression (consolidation), shear displacement and macro-rotation. The latter occurs when conditions are favorable (e.g. at a vertical interface) for the micro-rotation imposed by asymmetric stresses to become macro-rotation. When the length of the cone of depression is beyond ,2 times the thickness of the aquifer, simple shear on vertical planes with rotation is the predominant deformation mode. Otherwise, simple shear on horizontal planes is present. The predicted subsidence using the mechanics developed in this paper compares well with data from satellite-borne interferometric synthetic aperture radar. Copyright © 2009 John Wiley & Sons, Ltd. [source] A refined semi-analytic design sensitivity based on mode decomposition and Neumann seriesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2005Maenghyo Cho Abstract Among various sensitivity evaluation techniques, semi-analytical method (SAM) is quite popular since this method is more advantageous than analytical method (AM) and global finite difference method (GFD). However, SAM reveals severe inaccuracy problem when relatively large rigid body motions are identified for individual elements. Such errors result from the pseudo load vector calculated by differentiation using the finite difference scheme. In the present study, an iterative refined semi-analytical method (IRSAM) combined with mode decomposition technique is proposed to compute reliable semi-analytical design sensitivities. The improvement of design sensitivities corresponding to the rigid body mode is evaluated by exact differentiation of the rigid body modes and the error of SAM caused by numerical difference scheme is alleviated by using a Von Neumann series approximation considering the higher order terms for the sensitivity derivatives. In eigenvalue problems, the tendency of eigenvalue sensitivity is similar to that of displacement sensitivity in static problems. Eigenvector is decomposed into rigid body mode and pure deformation mode. The present iterative SAM guarantees that the eigenvalue and eigenvector sensitivities converge to the reliable values for the wide range of perturbed size of the design variables. Accuracy and reliability of the shape design sensitivities in static problems and eigenvalue problems by the proposed method are assessed through the various numerical examples. Copyright © 2004 John Wiley & Sons, Ltd. [source] Stress,strain behavior as related to surface topography and thickness uniformity in uni- and biaxially stretched PVDF/PMMA blendsPOLYMER ENGINEERING & SCIENCE, Issue 12 2007Xixian Zhou The influence of blend composition and processing conditions on the surface roughness and thickness uniformity of PVDF/PMMA blends were investigated in uniaxial and biaxial deformation mode for PVDV and PVDF/PMMA blends 70/30, 55/45, and 40/60 wt%. The addition of PMMA retards the thermal crystallizability of the blends and this allows rapid solidification into films with little or no crystallinities. Such precursors with lowered crystallinity were found to be easily uni- and biaxially stretched into uniform and transparent films in the temperature range between the glass transition temperature and cold crystallization temperature where they exhibit strain hardening. Thus, these blends are suitable for processes such as tenter frame biaxial stretching, double bubble film blowing, and stretch blow molding where they will exhibit good transparency and thickness uniformity. POLYM. ENG. SCI., 47:2110,2117, 2007. © 2007 Society of Plastics Engineers [source] A note on formulas for localized failure of frictional materials in compression and biaxial loading modesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2001Matthias Lambrecht Abstract The paper investigates aspects of the localization analysis of frictional materials. We derive closed formulas and diagrams for the inclination angle of critical discontinuity surfaces which develop in homogeneous compression and biaxial loading tests. The localization analysis is based on a Drucker,Prager-type elastoplastic hardening model for non-associated plastic flow at small strains, which we represent in spectral form. For this type of constitutive model, general analytical formulas for the so-called critical hardening modulus and the inclination angle of critical discontinuity surfaces are derived for the plane strain case. The subsequent treatment then specializes these formulas for the analysis of compression and biaxial loading modes. The key contribution here is a detailed analysis of plane strain deformation modes where the localized failure occurs after subsequent plastic flow. The derived formulas and diagrams can be applied to the checking of an accompanying localization analysis of frictional materials in finite-element computations. Copyright © 2001 John Wiley & Sons, Ltd. [source] A stabilized pseudo-shell approach for surface parametrization in CFD design problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 4 2002O. Soto Abstract A surface representation for computational fluid dynamics (CFD) shape design problems is presented. The surface representation is based on the solution of a simplified pseudo-shell problem on the surface to be optimized. A stabilized finite element formulation is used to perform this step. The methodology has the advantage of being completely independent of the CAD representation. Moreover, the user does not have to predefine any set of shape functions to parameterize the surface. The scheme uses a reasonable discretization of the surface to automatically build the shape deformation modes, by using the pseudo-shell approach and the design parameter positions. Almost every point of the surface grid can be chosen as design parameter, which leads to a very rich design space. Most of the design variables are chosen in an automatic way, which makes the scheme easy to use. Furthermore, the surface grid is not distorted through the design cycles which avoids remeshing procedures. An example is presented to demonstrate the proposed methodology. Copyright © 2002 John Wiley & Sons, Ltd. [source] A practical large-strain solid finite element for sheet formingINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2005Jue Wang Abstract An alternative approach for developing practical large-strain finite elements has been introduced and used to create a three-dimensional solid element that exhibits no locking or hourglassing, but which is more easily and reliably derived and implemented than typical reduced-integration schemes with hourglassing control. Typical large-strain elements for forming applications rely on reduced integration to remove locking modes that occur with the coarse meshes that are necessary for practical use. This procedure introduces spurious zero-energy deformation modes that lead to hourglassing, which in turn is controlled by complex implementations that involve lengthy derivations, knowledge of the material model, and/or undetermined parameters. Thus, for a new material or new computer program, implementation of such elements is a daunting task. Wang,Wagoner-3-dimensions (WW3D), a mixed, hexahedral, three-dimensional solid element, was derived from the standard linear brick element by ignoring the strain components corresponding to locking modes while maintaining full integration (8 Gauss points). Thus, WW3D is easily implemented for any material law, with little chance of programming error, starting from programming for a readily available linear brick element. Surprisingly, this approach and resulting element perform similarly or better than standard solid elements in a series of numerical tests appearing in the literature. The element was also tested successfully for an applied sheet-forming analysis problem. Many variations on the scheme are also possible for deriving special-purpose elements. Copyright © 2005 John Wiley & Sons, Ltd. [source] Reduced modified quadratures for quadratic membrane finite elementsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2004Craig S. Long Abstract Reduced integration is frequently used in evaluating the element stiffness matrix of quadratically interpolated finite elements. Typical examples are the serendipity (Q8) and Lagrangian (Q9) membrane finite elements, for which a reduced 2 × 2 Gauss,Legendre integration rule is frequently used, as opposed to full 3 × 3 Gauss,Legendre integration. This ,softens' these element, thereby increasing accuracy, albeit at the introduction of spurious zero energy modes on the element level. This is in general not considered problematic for the ,hourglass' mode common to Q8 and Q9 elements, since this spurious mode is non-communicable. The remaining two zero energy modes occurring in the Q9 element are indeed communicable. However, in topology optimization for instance, conditions may arise where the non-communicable spurious mode associated with the elements becomes activated. To effectively suppress these modes altogether in elements employing quadratic interpolation fields, two modified quadratures are employed herein. For the Q8 and Q9 membrane elements, the respective rules are a five and an eight point rule. As compared to fully integrated elements, the new rules enhance element accuracy due to the introduction of soft, higher-order deformation modes. A number of standard test problems reveal that element accuracy remains comparable to that of the under-integrated counterparts. Copyright © 2004 John Wiley & Sons, Ltd. [source] Synthesis of thiophene/phenylene co-oligomers.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2003We report the synthesis of various thiophene/phenylene co-oligomers with a total number of thiophene and benzene (phenylene) rings of 6 to 8. These compounds include a phenyl-capped sexithiophene, a thienyl-capped quaterphenylene, as well as block and alternating co-oligomers. The synthesis is based on either the Suzuki coupling reaction or the direct dimerization coupling. The latter method produces symmetric molecules with an even total ring number. These reaction schemes enabled us to obtain the target compounds in high quality. Although the resulting materials are difficult to dissolve in organic solvents and therefore difficult to identify by usual 1H nmr spectroscopy, they have successfully been identified through Fourier-transform ir spectroscopy. The specific group frequencies of ring-stretching and out-of-plane deformation modes are characteristic of the substitution pattern of the individual thiophene and benzene rings. [source] Raman spectroscopy of dimethyl sulphoxide and deuterated dimethyl sulphoxide at 298 and 77 KJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2002Wayde N. Martens Raman spectroscopy was used to determine the molecular behaviour of DMSO and DMSO- d6, and to compare it with that of DMSO in DMSO-intercalated kaolinites. For DMSO at 298 K two bands are observed at 2994 and 2913 cm,1 and are assigned to the antisymmetric and symmetric CH stretching modes. At 77 K the degeneracy of these bands is lost. Bands are now observed as antisymmetric bands at 3001, 2995 and 2988 cm,1 and symmetric bands at 2923, 2909 and 2885 cm,1, respectively. For the DMSO-intercalated low-defect kaolinite, the 2913 cm,1 band resolves into five component bands at 2882, 2907, 2917, 2920 and 2937 cm,1. The CD antisymmetric and symmetric stretching modes in the 298 K spectrum are found at 2250 and 2125 cm,1, respectively. Both bands show some asymmetry and further bands may be resolved at 2256 and 2244 cm,1 in the antisymmetric stretching region and at 2118 cm,1 in the symmetric stretching region. The spectra of the SO stretching region of DMSO and DMSO- d6 are complex with a band profile centred at 1050 cm,1. Three bands are curve resolved at 1058, 1042 and 1026 cm,1 attributed to the unassociated monomer and the out-of-phase and the in-phase vibrations of the dimer, respectively. Upon cooling to liquid nitrogen temperature, these three bands are observed at 1057, 1038 and 1019 cm,1. The spectra of the SO stretching region of DMSO- d6 are more complex because of the overlap of the DCD deformation modes with the SO stretching modes. The antisymmetric and symmetric stretching CS modes of DMSO are observed at 698 and 667 cm,1, shifting at 77 K to 705 and 672 cm,1. It is concluded that the structure of DMSO in DMSO-intercalated kaolinite is different from those of both liquid DMSO at 298 K and solid DMSO measured at 77 K. Copyright © 2002 John Wiley & Sons, Ltd. [source] Low frequency resonance Raman spectra of isolated , and , subunits of hemoglobin and their deuterated analoguesBIOPOLYMERS, Issue 5 2006Edyta Podstawka Abstract In an attempt to gain further insight into the nature of the low frequency vibrational modes of hemoglobin and its isolated subunits, a comprehensive study of several different isotopically labeled analogues has been undertaken and is reported herein. Specifically, the resonance Raman spectra, between 200 and 500 cm,1, are reported for the deoxy and ligated (CO and O2) forms of the isolated , and , subunits containing the natural abundance or various deuterated analogues of protoheme. The deuterated protoheme analogues studied include the 1,3,5,8-C2H3 -protoheme (d12- protoheme), the 1,3-C2H3 -protoheme (1,3- d6-protoheme), the 5,8-C2H3 -protoheme (5,8- d6-protoheme), and the meso-C2H4 -protoheme (d4-protoheme). The entire set of acquired spectra has been analyzed using a deconvolution procedure to help correlate the shifted modes with their counterparts in the spectra of the native forms. Interestingly, modes previously associated with so-called vinyl bending modes or propionate deformation modes are shown to be quite sensitive to deuteration of the peripheral methyl groups of the macrocycle, shifting by up to 12,15 cm,1, revealing their complex nature. Of special interest is the fact that shifts observed for the 1,3- d6- and 5,8- d6-protoheme analogues confirm the fact that certain modes are associated with a given portion of the macrocycle; i.e., only certain modes shift upon deuteration of the 1 and 3 methyl groups, while others shift upon deuteration of the 5 and 8 methyl groups. Compared with the spectra previously reported for the corresponding myoglobin derivatives, the data reported here reveal the appearance of several additional features that imply splitting of modes associated with the propionate groups or that are indicative of greater distortion of the heme prosthetic groups. © 2006 Wiley Periodicals, Inc. Biopolymers 83: 455,466, 2006 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] | ||||||||||||||||