Home About us Contact
|
Home About us Contact | ||
|
|
||
Principal Stresses (principal + stress)
Selected AbstractsMechanical Behavior and Stability of the Internal Membrane of the InCor Ventricular Assist DeviceARTIFICIAL ORGANS, Issue 11 2001Pedro Baroni Da Costa Teixeira Abstract: This paper describes and analyzes the mechanical behavior of the internal membrane of the InCor VAD (Heart Institute [InCor], University of São Paulo, Brazil), applying the knowledge and tools of structural engineering analysis. This membrane plays an important role in the operation of the ventricular assist device (VAD) because it separates the blood chamber from the pneumatic one, transmitting the pneumatic load to the blood, thus making the desired blood flow possible. The loading repeats itself every time the VAD beats. Therefore the performance, reliability, and durability of the membrane are critical for the performance of the VAD. The mathematical model is based on the large deflection theory of thin shells and on the finite element method. The snap-through instability phenomenon, which is responsible for transmission of the pneumatic load to the blood, was observed in the membrane both when modeled mathematically and experimentally. Principal stresses and strain distributions were obtained with this model at certain load levels along the pre- and postbuckling paths. [source] High-Speed and Wide-Angle Deflection Optical MEMS Scanner Using Piezoelectric ActuationIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 3 2010Takayuki Iseki Member Abstract A fast and wide deflection silicon-resonant torsional optical scanner driven by a piezoelectric actuator has been developed and patented. The scanner is composed of a 1-mm square mirror and two pairs of torsion beams and arms fabricated using microelectromechanical system (MEMS) processing of a silicon-on-insulator (SOI) wafer. According to calculations, at the same resonant driving frequency, the maximum principal stress of this structure was about one-third smaller than that of the usual structure having one pair of torsion beams. We achieved high frequency scanning of the optical beam with a large angular deflection up to 54° at 38 kHz with a 5 V peak-to-peak applied voltage using the bulk piezoelectric stack actuator, and up to 17° at 38 kHz with a 25 V peak-to-peak voltage using the unimorph actuator of a zinc oxide (ZnO) thin film. These results show that this scanner has the ability to perform the horizontal scanning for high-resolution extended graphics array (XGA) or super extended graphics array (SXGA) laser display. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Skin friction features of drilled CIP piles in sand from pile segment analysisINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2008Sungjune Lee Abstract Numerical pile segment analysis is conducted in this study with an advanced soil model to investigate the skin friction behaviour of a drilled Cast-In-Place (CIP) pile installed in sand. Although the interface between the sand and pile is considered rough, thin elements adjacent to the pile are used to include effects of localized shear. Unit weights of fluid concrete and accompanied changes in stress are considered as the effects of pile installation. Changes in effective stresses are the most prominent effect due to pile installation with a change in direction of the major principal stress from the vertical to the radial direction. Shear behaviour of the sand at the interface during the early shear stage is related to the contractive tendency of the sand at small strain levels. Changes in the stress field around the pile with little changes in volumetric strain take place during the early shear stage. Stress redistributions during the early shear stage depend on the direction of the major principal stress before shear. Results of the pile segment analyses for drilled CIP piles show good agreement with design methods. Parametric studies are used to characterize the effects of sand density and pile diameter on the skin friction behaviour of drilled CIP piles. Copyright © 2007 John Wiley & Sons, Ltd. [source] Computational issues in large strain elasto-plasticity: an algorithm for mixed hardening and plastic spinINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2005Francisco Javier Montáns Abstract In this paper an algorithm for large strain elasto-plasticity with isotropic hyperelasticity based on the multiplicative decomposition is formulated. The algorithm includes a (possible) constitutive equation for the plastic spin and mixed hardening in which the principal stress and principal backstress directions are not necessarily preserved. It is shown that if the principal trial stress directions are preserved during the plastic flow (as assumed in some algorithms) a plastic spin is inadvertently introduced for the kinematic/mixed hardening case. If the formulation is performed in the principal stress space, a rotation of the backstress is inadvertently introduced as well. The consistent linearization of the algorithm is also addressed in detail. Copyright © 2005 John Wiley & Sons, Ltd. [source] In situ stress measurements in a borehole close to the Nojima FaultISLAND ARC, Issue 3-4 2001Hiroaki Tsukahara AbstractIn situ stress was measured close to the fault associated with the 1995 Kobe Earthquake (Hyogo-ken Nanbu earthquake; January 1995; M7.2) using the hydraulic fracturing method. The measurements were made approximately 2 years after the earthquake. The measured points were approximately 40 m from the fault plane at depths of about 1500 m. The maximum and the minimum horizontal compressive stresses were 45 MPa and 31 MPa, respectively. The maximum compressive stress and the maximum shear stress are very small in comparison with those of other seismically active areas. The azimuth of the maximum horizontal compressive stress was estimated from the observed azimuths of well bore breakouts at depths between 1400 m and 1600 m and was found to be N135° (clockwise). The maximum stress axis is perpendicular to the fault strike, N45°. These features are interpreted in terms of a small frictional coefficient of the fault. The shear stress on the fault was released and dropped almost to zero during the earthquake and it has not yet recovered. Zero shear stress on the fault plane resulted from the perpendicular orientation of one of the principal stress to the fault plane. [source] Quantifying effects of particulate properties on powder flow properties using a ring shear testerJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2008Hao Hou Abstract Effects of particle size, morphology, particle density, and surface silicification, on powder flow properties were investigated using a ring shear tester. Flow properties were quantified by flow function (FF), that is, unconfined yield strength, fc, as a function of major principal stress. A total of 11 powders from three series of microcrystalline cellulose (MCC): Avicel (regular MCC, elongated particles), Prosolv (silicified MCC, elongated particles), and Celphere (spherical MCC), were studied. Particle size distribution in each type of MCC was systematically different. Within each series, smaller particles always led to poorer powder flow properties. The slope of FF line was correlated to degree of powder consolidation by external stress. A key mechanism of the detrimental effect of particle size reduction on flow properties was the larger powder specific surface area. Flow properties of Celphere were significantly better than Avicel of comparable particles size, suggesting spherical morphology promoted better powder flow properties. Flow properties of powders different in densities but similar in particle size, shape, and surface properties were similar. When corrected for density effect, higher particle density corresponded to better flow behavior. Surface silicification significantly improved flow properties of finer MCC, but did not improve those of coarser. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:4030,4039, 2008 [source] Digital simulation of the transformation of plane stressCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 1 2009Wei-Pin Lee Abstract In this study, we developed a computer program to simulate the transformation of plane stress by using Visual Basic.NET. We applied the equations of stress transformation to plane stress problems to calculate the stresses with respect to the 1,2 axes, which are rotated counterclockwise through an angle , about the x,y origin, and showed the visual results on the screen. In addition, we used animation to observe the change of plane stress. This program was then used in teaching courses, such as Mechanics of Materials and Linear Algebra. Use of the software may help students to understand principal stresses, principal axes, Mohr's circle, eigenvalues, eigenvectors, similar matrices, and invariants. © 2008 Wiley Periodicals, Inc. Comput Appl Eng Educ 17: 25,33, 2009; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae20180 [source] Non-linear behavior of mass concrete in three-dimensional problems using a smeared crack approachEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2005H. Mirzabozorg Abstract A smeared crack approach has been proposed to model the static and dynamic behavior of mass concrete in three-dimensional space. The proposed model simulates the tensile fracture on the mass concrete and contains pre-softening behavior, softening initiation, fracture energy conservation and strain rate effects under dynamic loads. The validity of the proposed model has been checked using the available experimental results under static and dynamic loads. The direct and indirect displacement control algorithms have been employed under incremental increasing static loads. It was found that the proposed model gives excellent results and crack profiles when compared with the available data under static loads. The Koyna Dam in India has been used to verify the dynamic behavior of the proposed model. It was found that the resulting crack profiles were in good agreement with the available experimental results. Finally, the Morrow Point Dam was analyzed, including the dam,reservoir interaction effects, to consider its non-linear seismic behavior. It was found that the resulting crack profiles were in good agreement with the contour of maximum principal stresses and no numerical instability occurred during the analysis. Copyright © 2004 John Wiley & Sons, Ltd. [source] Inclined standing contact fatigueFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2003B. ALFREDSSON ABSTRACT An experimental method is presented, in which a sphere is repeatedly pressed against a surface with an inclined contact load. The method is a development of the normally loaded standing contact fatigue test. Experiments are performed for three inclination angles below the angle of friction and the results are compared to those of the normally loaded standing contact fatigue test. The influence of tangential load on endurance limit load, number of cycles to crack initiation, contact mark appearance and crack behaviour in the surface as well as in cut views are evaluated. The surface crack behaviour outside the contact mark is analysed based on the cyclic contact stresses in the test specimen. The trajectories of the largest principal stresses are followed in both the surface view and in the cut view on the symmetry plane. These stress trajectories are compared to the experimental crack results. The connection between the inclined standing contact fatigue cracks and surface distress micro-cracks is also discussed. [source] ,Arching' effect in elastic polycrystals: implications for the variability of fatigue livesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 4 2002S. Pommier ABSTRACT The paper deals with a study of heterogeneous stress and strain distribution in polycrystals in relation with elastic anisotropy of grains. A similitude with the arching effect widely studied in granular materials is proposed and this concept is extended to heterogeneous polycrystals in which the load transfer is not binary in the way it is in granular media but may vary significantly and suddenly from one grain to another according to the crystal orientation to the load direction. Experiments and 3D finite element analyses show that though the individual orientation of grains is random, the strain and stress distribution is not. A network is formed inside the polycrystal whose scale is larger than the grain size. The load percolation network consists in heavily loaded links whose direction is coincident with the direction of the principal stresses. So, the typical scale for the variability of the local stresses is not the grain size but the size of the load percolation network. Since this scale is found to be rather large in particular for iron, zinc and copper, this effect should contribute significantly to the variability of the fatigue lives of notched vs. smooth components. [source] Discrete element modelling of deep penetration in granular soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2006M. J. Jiang Abstract This paper presents a numerical study on deep penetration mechanisms in granular materials with the focus on the effect of soil,penetrometer interface friction. A two-dimensional discrete element method has been used to carry out simulation of deep penetration tests on a granular ground that is under an amplified gravity with a K0 lateral stress boundary. The numerical results show that the deep penetration makes the soil near the penetrometer move in a complex displacement path, undergo an evident loading and unloading process, and a rotation of principal stresses as large as 180°. In addition, the penetration leads to significant changes in displacement and velocity fields as well as the magnitude and direction of stresses. In general, during the whole penetration process, the granular ground undergoes several kinds of failure mechanisms in sequence, and the soil of large deformation may reach a stress state slightly over the strength envelope obtained from conventional compression tests. Soil,penetrometer interface friction has clear effects on the actual penetration mechanisms. Copyright © 2005 John Wiley & Sons, Ltd. [source] Effect of element size on the static finite element analysis of steep slopesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2001Scott A. Ashford Abstract The accuracy of the computed stress distribution near the free surface of vertical slopes was evaluated in this study as a function of the element size, including aspect ratio. To accomplish this objective, a parametric study was carried out comparing stresses computed using the finite element method (FEM) to those obtained from a physical model composed of photoelastic material. The results of the study indicate a reasonable agreement between a gelatin model and the FEM model for shear stresses, and an overall good agreement between the two models for the principal stresses. For stresses along the top of the slope, the height of the element tends to be more important than width or aspect ratio, at least for aspect ratios up to 4. In all cases, the greatest difference between the two models occurs in the vicinity of the slope. Specifically, if H is defined as the slope height, an element height of H/10 appears to be adequate for the study of stresses deep within the slope, such as for typical embankment analyses. However, for cases where tensile stresses in the vicinity of the slope face which are critical, such as for the stability analysis of steep slopes, element heights as small as H/32, or higher-order elements, are necessary. Copyright © 2001 John Wiley & Sons, Ltd. [source] Force transmission of one- and two-piece morse-taper oral implants: a nonlinear finite element analysisCLINICAL ORAL IMPLANTS RESEARCH, Issue 4 2004Murat Cavit Çehreli Abstract Purpose: To compare force transmission behaviors of one-piece (1-P) and two-piece (2-P) morse-taper oral implants. Material and methods: A three-dimensional finite element model of a morse-taper oral implant and a solid abutment was constructed separately. The implant,abutment complex was embedded in a Ø 1.5 cm × 1.5 cm acrylic resin cylinder. Vertical and oblique forces of 50 N and 100 N were applied on the abutment and solved by two different analyses. First, contact analysis was performed in the implant,abutment complex to evaluate a 2-P implant. Then, the components were bonded with a separation force of 1020 N to analyze a 1-P implant. Results: Von Mises stresses in the implant, principal stresses, and displacements in the resin were the same for both designs under vertical loading. Under oblique loading, principal stresses and displacement values in the resin were the same, but the magnitudes of Von Mises stresses were higher in the 2-P implant. The principal stress distributions around both implants in the acrylic bone were similar under both loading conditions. Conclusion: 2-P implants experience higher mechanical stress under oblique loading. Nevertheless, the 1-P- or 2-P morse-taper nature of an implant is not a decisive factor for the magnitude and distribution of stresses, and displacements in supporting tissues. Résumé Le but de cette étude a été de comparer les comportements de la transmission de la force desimplants buccaux en deux pièces. Un modèle d'éléments finis tridimensionnels d'un implant buccal et d'un pilier solide ont été construits séparément. Le complexe implant/pilier a été enfoui dans un cylindre de résine acrylique d'un diamètre 1,5 × 1,5 cm. Des forces obliques et verticales de 50 et 100 N ont été appliquées sur les piliers et analysées par deux méthodes. D'abord, l'analyse de contraste a été effectuée dans le complexe implant/pilier pour évaluer un implant en deux pièces. Ensuite, les composants ont été reliés avec une force de séparation de 1020N pour analyser un implant en une pièce. Les stress de Von Mises dans l'implant, les principaux stress et les déplacements dans la résine étaient les mêmes pour les deux modèles sous charge verticale. Lorsqu'une charge oblique était appliquée, les stress principaux et les valeurs de déplacements dans la résine étaient semblables mais l'amplitude des stress de Von Mises était plus importante dans l'implant à deux pièces. Les distributions des stress principaux autour des deux implants dans l'os acrylique était semblable sous les deux conditions de charge. Les implants en deux pièces subissent un stress mécanique plus important sous une charge oblique. Cependant, l'implant en une ou deux pièces avec un cône morse n'est pas un facteur décisif sur l'amplitude et la distribution des stress, et les déplacements des tissus de support. Zusammenfassung Ziel: Die Kraftübertragungsverhältnisse von ein- und zweiteiligen oralen Implantaten mit konischem Sitz der Sekundärteile zu untersuchen. Material und Methode: Es wurde je ein separates dreidimensionales Finite Element Modell eines oralen Implantats mit konischem Sitz der Sekundärteile und ein Massivsekundärteil konstruiert. Der Implantat-Sekundärteilkomplex wurde in einem Zylinder aus Acryl mit Durchmesser 1.5cm und Länge 1.5cm eingebettet. Vertikale und schräge Kräfte von 50 N und 100 N wurden auf das Sekundärteil appliziert und durch zwei verschiedene Analysen ausgewertet. Zuerst wurde eine Kontaktanalyse im Implantat-Sekundärteilkomplex zur Auswertung eines zweiteiligen Implantats durchgeführt. Dann wurden die Komponenten mit einer Separationskraft von 1020 N verbunden, um ein einteiliges Implantat zu analysieren. Resultate: Unter vertikaler Belastung waren der Van Mises Stress im Implantat, der generelle Stress und die Displatzierung im Kunststoff für beide Konstruktionen gleich. Unter schräger Belastung waren der generelle Stress und die Displatzierungswerte im Kunststoff die gleichen, jedoch war das Ausmass des von Mises Stress im zweiteiligen Implantat grösser. Die generelle Stressverteilung im Akrylknochen um die Implantate war unter beiden Belastungsbedingungen ähnlich. Schlussfolgerung: Zweiteilige Implantate erleiden grösseren mechanischen Stress unter schräger Belastung. Jedoch ist die ein- oder zweiteilige Konstruktion mit konischem Sitz der Sekundärteile bei Implantaten kein entscheidender Faktor für das Ausmass und die Verteilung des Stresses und für die Displatzierung in den Verankerungsgeweben. Resumen Intención: Comparar los comportamientos de transmisión de fuerzas de implantes orales en cono morse de una o dos piezas. Material y métodos: Se construyeron separadamente un modelo tridimensional de elemento finito de un implante oral de cono morse y un pilar sólido. El complejo implante-pilar se embebió en un cilindro de resina acrílica de , 1.5 cm × 1.5 cm. Se aplicaron fuerzas oblicuas de 50 N y 100 N sobre el pilar y se resolvieron por medio de dos análisis diferentes. Primero, se llevó a cabo un análisis de contacto en el complejo implante-pilar para evaluar un implante de dos piezas. Después, se unieron los componentes con una fuerza de separación de 1020 N para analizar un implante de una sola pieza. Resultados: El estrés de Von Mises, el estrés principal, y el desplazamiento en la resina fueron los mismos para ambos diseños bajo carga vertical. Bajo carga oblicua, los valores de estrés principal y desplazamiento en resina fueron los mismos, pero la magnitud de los estreses de Von Mises fueron mayores en los implantes de dos piezas. Las distribuciones del estrés principal alrededor de ambos implantes in el hueso acrílico fueron similares bajo ambas condiciones de carga. Conclusión: Los implantes de dos piezas experimentan un estrés mecánico mas alto bajo carga oblicua. Sin embargo, la naturaleza de un implante de cono morse de una o dos piezas no es un factor decisivo en la magnitud y distribución de los estreses, y desplazamientos en los tejidos de soporte. [source] | |||||||||||||