Local Deformation (local + deformation)

Distribution by Scientific Domains

Selected Abstracts

The Characterization of Local Deformation and Fracture Properties , a Tool for Advanced Materials Design,

O. Kolednik
Novel experimental techniques have been recently developed to measure local deformation and fracture properties. The techniques comprise quantitative fracture surface analysis and in-situ loading experiments in combination with digital image analysis. Examples are presented, demonstrating how these methods can be used to investigate the damage evolution in materials, to improve tools for the numerical simulation, and for the design of more fracture resistant materials and components. [source]

Movement of the tongue during normal breathing in awake healthy humans

S. Cheng
Electromyographic (EMG) activity of the airway muscles suggest that genioglossus is the primary upper airway dilator muscle. However, EMG data do not necessarily translate into tissue motion and most imaging modalities are limited to assessment of the surfaces of the upper airway. In this study, we hypothesized that genioglossus moves rhythmically during the respiratory cycle and that the motion within is inhomogeneous. A ,tagged' magnetic resonance imaging technique was used to characterize respiratory-related tissue motions around the human upper airway in quiet breathing. Motion of airway tissues at different segments of the eupnoeic respiratory cycle was imaged in six adult subjects by triggering the scanner at the end of inspiration. Displacements of the ,tags' were analysed using the harmonic phase method (HARP). Respiratory timing was monitored by a band around the upper abdomen. The genioglossus moved during the respiratory cycle. During expiration, the genioglossus moved posteriorly and during inspiration, it moved anteriorly. The degree of motion varied between subjects. The maximal anteroposterior movement of a point tracked on the genioglossus was 1.02 ± 0.54 mm (mean ±s.d.). The genioglossus moved over the geniohyoid muscle, with minimal movement in other muscles surrounding the airway at the level of the soft palate. Local deformation of the tongue was analysed using two-dimensional strain maps. Across the respiratory cycle, positive strains within genioglossus reached peaks of 17.5 ± 9.3% and negative strains reached peaks of ,16.3 ± 9.3% relative to end inspiration. The patterns of strains were consistent with elongation and compression within a constant volume structure. Hence, these data suggest that even during respiration, the tongue behaves as a muscular hydrostat. [source]

The Characterization of Local Deformation and Fracture Properties , a Tool for Advanced Materials Design,

O. Kolednik
Novel experimental techniques have been recently developed to measure local deformation and fracture properties. The techniques comprise quantitative fracture surface analysis and in-situ loading experiments in combination with digital image analysis. Examples are presented, demonstrating how these methods can be used to investigate the damage evolution in materials, to improve tools for the numerical simulation, and for the design of more fracture resistant materials and components. [source]

The least-squares meshfree method for elasto-plasticity and its application to metal forming analysis

Kie-Chan Kwon
Abstract A new meshfree method for the analysis of elasto-plastic deformation is presented. The method is based on the proposed first-order least-squares formulation for elasto-plasticity and the moving least-squares approximation. The least-squares formulation for classical elasto-plasticity and its extension to an incrementally objective formulation for finite deformation are proposed. In the formulation, equilibrium equation and flow rule are enforced in least-squares sense, i.e. their squared residuals are minimized, and hardening law and loading/unloading condition are enforced pointwise at each integration point. The closest point projection method for the integration of rate-form constitutive equation is inherently involved in the formulation, and thus the radial-return mapping algorithm is not performed explicitly. The proposed formulation is a mixed-type method since the residuals are represented in a form of first-order differential system using displacement and stress components as nodal unknowns. Also the penalty schemes for the enforcement of boundary and frictional contact conditions are devised and the reshaping of nodal supports is introduced to avoid the difficulties due to the severe local deformation near contact interface. The proposed method does not employ structure of extrinsic cells for any purpose. Through some numerical examples of metal forming processes, the validity and effectiveness of the method are discussed. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Buffeting in transonic flow prediction using time-dependent turbulence model

A. Kourta
Abstract In transonic flow conditions, the shock wave/turbulent boundary layer interaction and flow separations on wing upper surface induce flow instabilities, ,buffet', and then the buffeting (structure vibrations). This phenomenon can greatly influence the aerodynamic performance. These flow excitations are self-sustained and lead to a surface effort due to pressure fluctuations. They can produce enough energy to excite the structure. The objective of the present work is to predict this unsteady phenomenon correctly by using unsteady Navier,Stokes-averaged equations with a time-dependent turbulence model based on the suitable (k,,) turbulent eddy viscosity model. The model used is based on the turbulent viscosity concept where the turbulent viscosity coefficient (C,) is related to local deformation and rotation rates. To validate this model, flow over a flat plate at Mach number of 0.6 is first computed, then the flow around a NACA0012 airfoil. The comparison with the analytical and experimental results shows a good agreement. The ONERA OAT15A transonic airfoil was chosen to describe buffeting phenomena. Numerical simulations are done by using a Navier,Stokes SUPG (streamline upwind Petrov,Galerkin) finite-element solver. Computational results show the ability of the present model to predict physical phenomena of the flow oscillations. The unsteady shock wave/boundary layer interaction is described. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Microstrain and grain-size analysis from diffraction peak width and graphical derivation of high-pressure thermomechanics

Yusheng Zhao
An analytical method is presented for deriving the thermomechanical properties of polycrystalline materials under high-pressure (P) and high-temperature (T) conditions. This method deals with non-uniform stress among heterogeneous crystal grains and surface strain in nanocrystalline materials by examining peak-width variation under different P,T conditions. Because the method deals directly with lattice d spacing and local deformation caused by stress, it can be applied to process any diffraction profile, independent of detection mode. In addition, a correction routine is developed using diffraction elastic ratios to deal with severe surface strain and/or strain anisotropy effects related to nano-scale grain sizes, so that significant data scatter can be reduced in a physically meaningful way. Graphical illustration of the resultant microstrain analysis can identify micro/local yields at the grain-to-grain interactions resulting from high stress concentration, and macro/bulk yield of the plastic deformation over the entire sample. This simple and straightforward approach is capable of revealing the corresponding micro and/or macro yield stresses, grain crushing or growth, work hardening or softening, and thermal relaxation under high- P,T conditions, as well as the intrinsic residual strain and/or surface strain in the polycrystalline bulk. In addition, this approach allows the instrumental contribution to be illustrated and subtracted in a straightforward manner, thus avoiding the potential complexities and errors resulting from instrument correction. Applications of the method are demonstrated by studies of ,-SiC (6H, moissanite) and of micro- and nanocrystalline nickel by synchrotron X-ray and time-of-flight neutron diffraction. [source]

Front Cover Picture: Laser & Photon.

Rev. 4(4)/2010
Illustration of local deformation in an isolated carbon nanotube due to the pressure applied through the apex of a nano-tip. By sensing this local deformation by means of Raman shift in TERS, the sample can be imaged with extremely high spatial resolution.(Picture: P. Verma et al., pp. 548,561, in this issue) [source]

Determination of the dynamics of restored teeth by 3D electronic speckle pattern interferometry,

H. Lang
Abstract Background and Objectives The difficulties typically encountered in studying the effects of restorations on tooth reinforcement are often due to the 3-dimensional (3D) nature of deformation. Therefore, electronic 3D-Speckle-Interferometry (3D-ESPI) was used to assess the impact of different restorative materials on the deformation of teeth. Study Design/Materials and Methods Small and large MOD-preparations in extracted premolars were restored with gold inlays, ceramic inlays, composite resin inlays, amalgam, or composite resin. The restorations and cusps were loaded (90 N) and the deformation was assessed by 3D-ESPI. Results Teeth with small restorations were deformed only slightly and the differences between the materials were minimal (P>0.05). In contrast, teeth with large restorations displayed material-specific deformation patterns: (a) all materials led to decreased deformation as compared with unfilled teeth, (b) elastic materials caused only local deformation, (c) non-adhesive materials resulted in translation of the restoration and marginal discrepancies, (d) adhesive inlays brought about increased deformation of the luting resin composite, (e) loading of the cusps caused higher deformation than loading of the restorations, and (f) bonded restorations stabilized the cusps. Conclusions The results show that the deformation pattern of restored teeth is material-specific but the extent of deformation is primarily limited by the remaining tooth substance. Lasers Surg. Med. 34:300,309, 2004. © 2004 Wiley-Liss, Inc. [source]

ProcDef: Local-to-global Deformation for Skeleton-free Character Animation

Takashi Ijiri
Abstract Animations of characters with flexible bodies such as jellyfish, snails, and, hearts are difficult to design using traditional skeleton-based approaches. A standard approach is keyframing, but adjusting the shape of the flexible body for each key frame is tedious. In addition, the character cannot dynamically adjust its motion to respond to the environment or user input. This paper introduces a new procedural deformation framework (ProcDef) for designing and driving animations of such flexible objects. Our approach is to synthesize global motions procedurally by integrating local deformations. ProcDef provides an efficient design scheme for local deformation patterns; the user can control the orientation and magnitude of local deformations as well as the propagation of deformation signals by specifying line charts and volumetric fields. We also present a fast and robust deformation algorithm based on shape-matching dynamics and show some example animations to illustrate the feasibility of our framework. [source]

Numerical analysis of a new Eulerian,Lagrangian finite element method applied to steady-state hot rolling processes

Josef Synka
Abstract A finite element code for steady-state hot rolling processes of rigid,visco-plastic materials under plane,strain conditions was developed in a mixed Eulerian,Lagrangian framework. This special set up allows for a direct calculation of the local deformations occurring at the free surfaces outside the contact region between the strip and the work roll. It further simplifies the implementation of displacement boundary conditions, such as the impenetrability condition. When applied to different practical hot rolling situations, ranging from thick slab to ultra-thin strip rolling, the velocity,displacement based model (briefly denoted as vu-model) in this mixed Eulerian,Lagrangian reference system proves to be a robust and efficient method. The vu-model is validated against a solely velocity-based model (vv-model) and against elementary methods based on the Kármán,Siebel and Orowan differential equations. The latter methods, when calibrated, are known to be in line with experimental results for homogeneous deformation cases. For a massive deformation it is further validated against the commercial finite-element software package Abaqus/Explicit. It is shown that the results obtained with the vu-model are in excellent agreement with the predictions of the vv-model and that the vu-model is even more robust than its vv-counterpart. Throughout the study we assumed a rigid cylindrical work roll; only for the homogeneous test case, we also investigated the effect of an elastically deformable work roll within the frame of the Jortner Green's function method. The new modelling approach combines the advantages of conventional Eulerian and Lagrangian modelling concepts and can be extended to three dimensions in a straightforward manner. Copyright © 2004 John Wiley & Sons, Ltd. [source]

The Vibrational Behavior of Bladed Disks in Consideration of Friction Damping and Contact Elasticity

Christian Siewert
Rotating turbine blading is subjected to fluctuating gas forces during operation that cause blade vibrations. One of the main tasks in the design of turbomachinery blading is the reduction of the vibration amplitudes of the blades to avoid high resonance stresses that could damage the blading. The vibration amplitudes of the blades can be reduced significantly to a reasonable amount by means of friction damping devices such as underplatform dampers. In the case of blade vibrations, relative displacements between the friction damping devices and the neighboring blades occur and friction forces are generated that provide additional damping to the structure due to the dry friction energy dissipation. In real turbomachinery applications, spatial blade vibrations caused by a complex blade geometry and distributed excitation forces acting on the airfoil accur. Therefore, a three dimensional model including an appropriate spatial contact model to predict the generalized contact forces is necessary to describe the vibrational behavior of the blading with sufficient accuracy, see [1] and [2]. In this paper the contact model presented in [2] is extended to include also local deformations in the contacts between underplatform dampers and the contact surfaces of the adjacent blades. The additional elasticity in the contact influences the resonance frequency of the coupled bladed disk assembly. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Beanspruchungsanalyse von Holzbauteilen durch 2D-Photogrammetrie

BAUTECHNIK, Issue 2 2005
Bettina Franke Dipl.-Ing.
Für die Bewertung der Tragsicherheit von Bauteilen aus Voll- und Brettschichtholz in Lasteinleitungs- und Störbereichen mittels der Bruchmechanik ist die Kenntnis von kritischen Bruchkennwerten Voraussetzung. Realitätsnahe Kennwerte können aus der Kombination experimenteller Untersuchungen zur Bestimmung der Rißaufweitung und der Rißlänge mit daran anschließender FE-Simulation gewonnen werden. Aufgrund der, bisher bei konventionellen Meßverfahren, nicht ausreichenden Zuordnung der Meßwerte taktil applizierter Meßaufnehmer lag es nahe das Rißwachstum mit Hilfe der Photogrammetrie zu untersuchen. Mit dem entwickelten Meßsystem ist nunmehr die Möglichkeit der exakten Vermessung der Rißgeometrie zur Bestimmung von bruchmechanischen Kennwerten gegeben. Zusätzlich ermöglicht der Einsatz der Photogrammetrie die Verdichtung der Anzahl variierender diskreter Meßpunkte, so daß ein deutlich vollständigeres Bild der örtlichen Verformungen gewonnen, und damit die Aussagekraft eines Versuchs wesentlich verbessert werden kann. Strain analysis of solid wood and glued laminated timber members by close range photogrammetry. The assumption of critical fracture mechanics parameters for the evaluation of the load-bearing safety of structural units of full and board laminated timber in loaded areas and disturbance ranges the use of fracture mechanics is required. Realistic parameters can be gained only from experimental investigations that are transferred to the determination of the crack opening and the crack length with subsequent FE-simulation. Due to the insufficient appropriation of measured data gained by tactile position encoders in conventional measuring procedures it is advisable to investigate crack growth with the help of the photogrammetry. Using the developed measuring system it is now possible to measure the crack geometry exactly for the determination of fracture mechanics parameters. Additionally a complete picture of the local deformations and the validity of a test can be improved considerably by the possibility of the varying number of discrete measuring points. [source]