Academic literature on the topic 'Load induced Anisotropy'
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Journal articles on the topic "Load induced Anisotropy"
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Dmowski, Wojtek, and Takeshi Egami. "Observation of structural anisotropy in metallic glasses induced by mechanical deformation." Journal of Materials Research 22, no. 2 (February 2007): 412–18. http://dx.doi.org/10.1557/jmr.2007.0043.
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We have investigated atomic structure of a Fe81B13Si4C2 metallic glass after mechanical creep deformation. We determined the structure function and pair density function resolved for azimuthal angle using x-ray scattering and a two-dimensional detector. The results are analyzed by the spherical harmonics expansion, and are compared to the often-used simple analysis of the anisotropic pair density function determined by measuring the structure function along two directions with respect to the stress. We observed uniaxial structural anisotropy in a sample deformed during creep experiment. The observed macroscopic shear strain is explained in terms of local bond anisotropy induced by deformation at elevated temperature. The bond anisotropy is a “memory” of this deformation after load was removed. We showed that use of sine-Fourier transformation to anisotropic glass results in systematic errors in the atomic pair distribution function.
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Kahraman, Hasan, and Edmund Haberstroh. "DIRECTION-DEPENDENT AND MULTIAXIAL STRESS-SOFTENING BEHAVIOR OF CARBON BLACK–FILLED RUBBER." Rubber Chemistry and Technology 87, no. 1 (March 1, 2014): 139–51. http://dx.doi.org/10.5254/rct.13.87910.
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ABSTRACT The mechanical behavior of filled rubbers depends on the maximum stretch previously reached and consequently on the induced stress softening. This softening effect is referred to as the Mullins effect. Current investigations point out that the Mullins effect exhibits a significant directional dependence, which calls for an anisotropic material model. But for the formulation and validation of anisotropic material models, there is still a lack of suitable experimental data. For this the purpose, experiments based on chloroprene rubber (CR) are reported. To trace the anisotropic Mullins effect, the standard test method for characterization of the isotropic mechanical behavior must be extended. The appropriate type of specimen enables us to perform multiple load steps with alternating load directions. After repeated stretching in the same direction, a subsequent first uniaxial loading in any other direction is characterized by a stiffer stress–strain behavior compared with the stabilized curve of the previous primary load. Hence, the experimental results confirm the deformation-induced anisotropy. To identify the multiaxial material behavior after the prestretching in one direction, a biaxial tensile-testing machine is developed. A specific property of the biaxial tensile-testing machine is the independent control of both the loading axes. Thus, the rubber material can be subjected to arbitrary loading histories. Therefore, a cross-shaped specimen with four arms is used. Multiple slits parallel to the sides on each arm ensures the homogenous uniaxial load condition in the primary load. In the secondary load step, the loading axis, which was previously inactive, is moved in a uniform manner as the master axis or in any arbitrary defined ratio. The experimental results confirm the deformation-induced anisotropy of the Mullins effect. In summary, the material behavior significantly results from the deformation mode and the loading direction applied in the loading history.
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Litewka, A. "Load-induced oriented damage and anisotropy of rock-like materials." International Journal of Plasticity 19, no. 12 (December 2003): 2171–91. http://dx.doi.org/10.1016/s0749-6419(03)00064-0.
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Karasahin, Mustafa. "An anisotropic model of unbound granular material under repeated loading." Thermal Science 23, Suppl. 1 (2019): 295–302. http://dx.doi.org/10.2298/tsci181021043k.
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The base and subbase layers of a pavement are compacted to the desired density by rollers. This cause the anisotropy in other words the layer more stiffer in the vertical direction than the horizontal direction. In the study inherent and stress induced anisotropy were measured by using the repeated load triaxial test equipment which is able to cycle both confining and axial pressure. The test results were then modelled using the stepwise regression. A new cross anisotropic model was proposed to predict the unbound stress-strain behavior. The proposed model is able to predict the axial strain more accurately than the radial strain.
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De Marchi, Nico, WaiChing Sun, and Valentina Salomoni. "Shear Wave Splitting and Polarization in Anisotropic Fluid-Infiltrating Porous Media: A Numerical Study." Materials 13, no. 21 (November 5, 2020): 4988. http://dx.doi.org/10.3390/ma13214988.
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The triggering and spreading of volumetric waves in soils, namely pressure (P) and shear (S) waves, developing from a point source of a dynamic load, are analyzed. Wave polarization and shear wave splitting are innovatively reproduced via a three-dimensional Finite Element research code upgraded to account for fast dynamic regimes in fully saturated porous media. The mathematical–numerical model adopts a u-v-p formulation enhanced by introducing Taylor–Hood mixed finite elements and the stability features of the solution are considered by analyzing different implemented time integration strategies. Particularly, the phenomena have been studied and reconstructed by numerically generating different types of medium anisotropy accounting for (i) an anisotropic solid skeleton, (ii) an anisotropic permeability tensor, and (iii) a Biot’s effective stress coefficient tensor. Additionally, deviatoric-volumetric coupling effects have been emphasized by specifically modifying the structural anisotropy. A series of analyses are conducted to validate the model and prove the effectiveness of the results, from the directionality of polarized vibrations, the anisotropy-induced splitting, up to the spreading of surface waves.
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Thomopoulos, Stavros, Gregory M. Fomovsky, Preethi L. Chandran, and Jeffrey W. Holmes. "Collagen Fiber Alignment Does Not Explain Mechanical Anisotropy in Fibroblast Populated Collagen Gels." Journal of Biomechanical Engineering 129, no. 5 (February 15, 2007): 642–50. http://dx.doi.org/10.1115/1.2768104.
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Many load-bearing soft tissues exhibit mechanical anisotropy. In order to understand the behavior of natural tissues and to create tissue engineered replacements, quantitative relationships must be developed between the tissue structures and their mechanical behavior. We used a novel collagen gel system to test the hypothesis that collagen fiber alignment is the primary mechanism for the mechanical anisotropy we have reported in structurally anisotropic gels. Loading constraints applied during culture were used to control the structural organization of the collagen fibers of fibroblast populated collagen gels. Gels constrained uniaxially during culture developed fiber alignment and a high degree of mechanical anisotropy, while gels constrained biaxially remained isotropic with randomly distributed collagen fibers. We hypothesized that the mechanical anisotropy that developed in these gels was due primarily to collagen fiber orientation. We tested this hypothesis using two mathematical models that incorporated measured collagen fiber orientations: a structural continuum model that assumes affine fiber kinematics and a network model that allows for nonaffine fiber kinematics. Collagen fiber mechanical properties were determined by fitting biaxial mechanical test data from isotropic collagen gels. The fiber properties of each isotropic gel were then used to predict the biaxial mechanical behavior of paired anisotropic gels. Both models accurately described the isotropic collagen gel behavior. However, the structural continuum model dramatically underestimated the level of mechanical anisotropy in aligned collagen gels despite incorporation of measured fiber orientations; when estimated remodeling-induced changes in collagen fiber length were included, the continuum model slightly overestimated mechanical anisotropy. The network model provided the closest match to experimental data from aligned collagen gels, but still did not fully explain the observed mechanics. Two different modeling approaches showed that the level of collagen fiber alignment in our uniaxially constrained gels cannot explain the high degree of mechanical anisotropy observed in these gels. Our modeling results suggest that remodeling-induced redistribution of collagen fiber lengths, nonaffine fiber kinematics, or some combination of these effects must also be considered in order to explain the dramatic mechanical anisotropy observed in this collagen gel model system.
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Barret, C., and S. Baste. "Effective Elastic Stiffnesses of an Anisotropic Medium Permeated by Tilted Cracks." Journal of Applied Mechanics 66, no. 3 (September 1, 1999): 680–86. http://dx.doi.org/10.1115/1.2791562.
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This paper is concerned with the relationship between the effective stiffness tensor and the intensity of damage in individual modes for an anisotropic material with tilted cracks. The predictions are compared favorably with the experimentally measured load-induced changes of the 13 stiffnesses of a two-dimensional C/C-SiC ceramic matrix composite subjected to an off-axis solicitation. By taking into account the thickness of the cracks, it is possible to understand the change of the elastic anisotropy of the material and of its inelastic strain.
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Prioul, Romain, Andrey Bakulin, and Victor Bakulin. "Nonlinear rock physics model for estimation of 3D subsurface stress in anisotropic formations: Theory and laboratory verification." GEOPHYSICS 69, no. 2 (March 2004): 415–25. http://dx.doi.org/10.1190/1.1707061.
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We develop a rock physics model based on nonlinear elasticity that describes the dependence of the effective stiffness tensor as a function of a 3D stress field in intrinsically anisotropic formations. This model predicts the seismic velocity of both P‐ and S‐waves in any direction for an arbitrary 3D stress state. Therefore, the model overcomes the limitations of existing empirical velocity‐stress models that link P‐wave velocity in isotropic rocks to uniaxial or hydrostatic stress. To validate this model, we analyze ultrasonic velocity measurements on stressed anisotropic samples of shale and sandstone. With only three nonlinear constants, we are able to predict the stress dependence of all five elastic medium parameters comprising the transversely isotropic stiffness tensor. We also show that the horizontal stress affects vertical S‐wave velocity with the same order of magnitude as vertical stress does. We develop a weak‐anisotropy approximation that directly links commonly measured anisotropic Thomsen parameters to the principal stresses. Each Thomsen parameter is simply a sum of corresponding background intrinsic anisotropy and stress‐induced contribution. The stress‐induced part is controlled by the difference between horizontal and vertical stresses and coefficients depending on nonlinear constants. Thus, isotropic rock stays isotropic under varying but hydrostatic load, whereas transversely isotropic rock retains the same values of dimensionless Thomsen parameters. Only unequal horizontal and vertical stresses alter anisotropy. Since Thomsen parameters conveniently describe seismic signatures, such as normal‐moveout velocities and amplitude‐variation‐with‐offset gradients, this approximation is suitable for designing new methods for the estimation of 3D subsurface stress from multicomponent seismic data.
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Yeh, Wei-Ching, Chia-Dou Ho, and Wen-Fung Pan. "An endochronic theory accounting for deformation induced anisotropy of metals under biaxial load." International Journal of Plasticity 12, no. 8 (January 1996): 987–1004. http://dx.doi.org/10.1016/s0749-6419(96)00038-1.
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Niazi, M. S., V. Timo Meinders, H. H. Wisselink, C. H. L. J. ten Horn, Gerrit Klaseboer, and A. H. van den Boogaard. "A Plasticity Induced Anisotropic Damage Model for Sheet Forming Processes." Key Engineering Materials 554-557 (June 2013): 1245–51. http://dx.doi.org/10.4028/www.scientific.net/kem.554-557.1245.
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The global fuel crisis and increasing public safety concerns are driving the automotive industry to design high strength and low weight vehicles. The development of Dual Phase (DP) steels has been a big step forward in achieving this goal. DP steels are used in many automotive body-in-white structural components such as A and B pillar reinforcements, longitudinal members and crash structure parts. DP steels are also used in other industrial sectors such as precision tubes, train seats and Liquid Petroleum Gas (LPG) cylinders. Although the ductility of DP steel is higher than classical high strength steels, it is lower than that of classical deep drawing steels it has to replace. The low ductility of DP steels is attributed to damage development. Damage not only weakens the material but also reduces the ductility by formation of meso-cracks due to interacting micro defects. Damage in a material usually refers to presence of micro defects in the material. It is a known fact that plastic deformation induces damage in DP steels. Therefore damage development in these steels have to be included in the simulation of the forming process. In ductile metals, damage leads to crack initiation. A crack is anisotropic which makes damage anisotropic in nature. However, most researchers assume damage to be an isotropic phenomenon. For correct and accurate simulation results, damage shall be considered as anisotropic, especially if the results are used to determine the crack propagation direction. This paper presents an efficient plasticity induced anisotropic damage model to simulate complex failure mechanisms and accurately predict failure in macro-scale sheet forming processes. Anisotropy in damage can be categorized based on the cause which induces the anisotropy, i.e. the loading state and the material microstructure. According to the Load Induced Anisotropic Damage (LIAD) model, if the material is deformed in one direction then damage will be higher in this direction compared to the other two orthogonal directions, irrespective of the microstructure of the material. According to Material Induced Anisotropic Damage (MIAD) model, if there is an anisotropy in shape or distribution of the particles responsible for damage (hard second phase particles, inclusions or impurities) then the material will have different damage characteristics for different orientations in the sheet material. The LIAD part of the damage model is a modification of Lemaitre’s (ML) anisotropic damage model. Modifications are made for damage development under compression state and influence of strain rate on damage, and are presented in this paper. Viscoplastic regularization is used to avoid pathological mesh dependency. The MIAD part of the model is an extension of the LIAD model. Experimental evidence is given of the MIAD phenomenon in DP600 steel. The experimental analysis is carried out using tensile tests, optical strain measurement system (ARAMIS) and scanning electron microscopy. The extension to incorporate MIAD in the ML anisotropic damage model is presented in this paper as well. The paper concludes with a validation of the anisotropic damage model for different applications. The MIAD part of the model is validated by experimental cylindrical cup drawing wheras the LIAD part of the model is validated by the cross die drawing process.
Dissertations / Theses on the topic "Load induced Anisotropy"
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Speck, Kerstin. "Beton unter mehraxialer Beanspruchung." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1216628091575-43714.
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Diese Arbeit basiert auf der Untersuchung von hochfesten und ultrahochfesten Betonen mit und ohne Fasern unter zwei- und dreiaxialer Druckbeanspruchung. Die Auswirkung der unterschiedlichen Betonzusammensetzung ist für verschiedene Beanspruchungen nicht gleich ausgeprägt, dennoch konnten grundlegende Zusammenhänge herausgearbeitet werden. Anhand der Bruchbilder konnten die drei Versagensmechanismen Druck-, Spalt- und Schubbruch identifiziert werden, deren Charakteristik über die Kalibrierung an vier speziellen Versuchswerten direkt in das Bruchkriterium einfließen. Dieses stellt eine Erweiterung der Formulierung von OTTOSEN dar, so dass das spröde und z. T. anisotrope Verhalten von Hochleistungsbeton berücksichtigt wird. Die beobachteten Spannungs-Dehnungs-Verläufe korrelieren mit den Versagensformen. Deshalb wird ein Stoffgesetz getrennt für den Druck- und den Zugmeridian aufgestellt, dessen Parameter sich mit zunehmendem hydrostatischen Druck verändern. In die Anfangswerte fließen die Betonzusammensetzung und herstellungsbedingte Anisotropien ein. Die lastinduzierte Anisotropie infolge einer gerichteten Mikrorissbildung wird in dem vorgestellten Stoffgesetzt über richtungsabhängige Parameter ebenfalls berücksichtigt.
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Speck, Kerstin. "Beton unter mehraxialer Beanspruchung: Ein Materialgesetz für Hochleistungsbetone unter Kurzzeitbelastung." Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A23705.
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Diese Arbeit basiert auf der Untersuchung von hochfesten und ultrahochfesten Betonen mit und ohne Fasern unter zwei- und dreiaxialer Druckbeanspruchung. Die Auswirkung der unterschiedlichen Betonzusammensetzung ist für verschiedene Beanspruchungen nicht gleich ausgeprägt, dennoch konnten grundlegende Zusammenhänge herausgearbeitet werden. Anhand der Bruchbilder konnten die drei Versagensmechanismen Druck-, Spalt- und Schubbruch identifiziert werden, deren Charakteristik über die Kalibrierung an vier speziellen Versuchswerten direkt in das Bruchkriterium einfließen. Dieses stellt eine Erweiterung der Formulierung von OTTOSEN dar, so dass das spröde und z. T. anisotrope Verhalten von Hochleistungsbeton berücksichtigt wird. Die beobachteten Spannungs-Dehnungs-Verläufe korrelieren mit den Versagensformen. Deshalb wird ein Stoffgesetz getrennt für den Druck- und den Zugmeridian aufgestellt, dessen Parameter sich mit zunehmendem hydrostatischen Druck verändern. In die Anfangswerte fließen die Betonzusammensetzung und herstellungsbedingte Anisotropien ein. Die lastinduzierte Anisotropie infolge einer gerichteten Mikrorissbildung wird in dem vorgestellten Stoffgesetzt über richtungsabhängige Parameter ebenfalls berücksichtigt.
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Costa, Luís António Veiga da. "Fendas de secagem em vigas de madeira: causas, efeitos na capacidade resistente e métodos de reparação." Master's thesis, 2015. http://hdl.handle.net/1822/40597.
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Dissertação de mestrado integrado em Engenharia CivilA madeira é um material higroscópico, e por isso, está em constante troca com o ambiente circundante. Sob condições de humidade relativa e temperatura constantes, a madeira tende a atingir um teor em água de equilíbrio constante. Além de higroscópica, a madeira é heterogénea, anisotrópica e retrátil. No entanto, o comportamento retrátil da madeira só se verifica, quando esta varia de teor em água para patamares inferiores ao seu ponto de saturação das fibras, ponto a partir do qual a madeira começa a perder água higroscópica contida nas paredes celulares. A heterogeneidade e a anisotropia da madeira, fazem com que a retração da madeira seja distinta para as três direções fundamentais de crescimento. A retração tangencial é cerca de 1.5 a 2 vezes superior à radial. Este diferencial nas retrações transversais da madeira, são a principal causa da ocorrência de fendas longitudinais às fibras da madeira. Estas ocorrem normalmente devido a processos de secagem não controlados, que resultam em tensões de tração internas transversais às fibras superiores às resistentes, sendo esta uma das propriedades fracas do material lenhoso. Estas fendas desenvolvem-se segundo planos radiais. Uma madeira com um coeficiente de anisotropia (relação entre a retração tangencial e radial) próximo da unidade, considera-se como sendo estável dimensionalmente, e menos propensa ao surgimento de fendas e empenos. No entanto, as condições higrotérmicas do ambiente circundante de uma peça de madeira não são constantes, fazendo com que a madeira perca e ganhe humidade em função da variação do clima circundante, sempre em busca do teor em água de equilibro. Como o transporte de humidade no interior da madeira é lento, as camadas externas de uma dada secção atingem mais rapidamente o teor em água de equilibro que as camadas internas. Esta diferente entre teores em água entre camadas adjacentes, designado como gradiente de humidade, resulta num diferencial de extensões de retração, e por conseguinte em tensões internas, que quando ultrapassam a capacidade resistente à tração transversal às fibras se libertam em forma de fenda. São vários os fatores que estão na génese do aparecimento de fendas e do modo como estas afetam a resistência dos elementos estruturais de madeira. Contudo existem métodos e técnicas de reparação especialmente desenvolvidos, para minimizar ou anular o seu efeito negativo na capacidade portante dos elementos estruturais de madeira.
Wood is a hygroscopic material, and therefore, is in continuous exchange with the surrounding environment. Under conditions of relative humidity and constant temperature, the wood tends to reach a constant water content. In addition to the hygroscopic nature, wood is heterogeneous, and anisotropic retractable. However, the behavior of wood retractable only occurs, when their water content change in a range below fibers saturation point, from which the wood begins to lose hygroscopic water contained in cell walls. The heterogeneity and anisotropy of timber, make retraction of the timber be different for the three fundamental directions. The tangential shrinkage is about 1.5 to 2 times the radial direction. This difference in transverse retraction of the timber, are the primary cause of the occurrence of longitudinal cracks on wood fibers. Is typically occurs because of uncontrolled drying processes which result in transverse internal tensile stresses higher than the resistant fibers, this being a poor property of timber. These cracks develop radial planes. With a coefficient of anisotropy (the ratio between tangential and radial shrinkage) close to the unit, is considered to be dimensionally stable, and less likely to cracks and warp. However, the hygrothermal conditions of the surrounding environment of a piece of wood are not constant, causing losses and gains of wood moisture content in function of the variation in humidity of the surrounding atmosphere, always seeking the equilibrium water content. As the moisture transport within timber is slow, the outer layers of a given section quickly reach the equilibrium water content of the outer layers. This different between water contents between adjacent layers, referred to as moisture gradient, giving rise differential shrinkage extensions, and therefore in internal stresses, which when exceed the load bearing capacity transversal to the fibers are released in the form of cracks. There are several factors that are at the origin of cracks and how these affect the resistance of structural elements of wood. However there are methods and repair techniques specifically designed to minimize or cancel its negative effect on the bearing capacity of the structural elements of wood.
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Ho, Chia-Dou, and 何加道. "Experimental Verification of An Endochronic Theory Accounted for Deformation Induced Anisotropy under Biaxial Loads." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/29418589288218875645.
Full textConference papers on the topic "Load induced Anisotropy"
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Yoo, Jin-Hyeong, James B. Restorff, Marilyn Wun-Fogle, and Alison B. Flatau. "Induced Magnetic Anisotropy in Stress-Annealed Galfenol Laminated Rods." In ASME 2008 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. ASMEDC, 2008. http://dx.doi.org/10.1115/smasis2008-636.
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The recent discovery of Iron-Gallium alloy (Galfenol) as a “large” magnetostrictive material (as high as 400 ppm) offers a particularly promising transducer material that combines largely desirable mechanical attributes with superior magnetic properties [1]. The high permeability of this material makes it easy to magnetize, however it also causes a relatively low cutoff frequency in dynamic applications, above which eddy currents form and introduce significant power losses. To reduce the eddy current losses, magnetostrictive drivers used in dynamic applications are commonly laminated. A second transducer design consideration is the introduction of an initial alignment of domains inside of the material to maximize the magnetostriction performance. It is common to achieve this by imposing an external compressive prestress to align magnetic moments perpendicular to the direction of actuation. An alternative to the application of an external prestress is to build-in a uniaxial magnetic anisotropy through stress annealing [2]. Stress annealing is a high temperature process with simultaneous application of an external load and subsequent cooling under load in which the magnetic moment alignment developed at temperature is retained upon removal from the stress annealing fixture. The external load needed to build in a useful uniaxial magnetic anisotropy in Galfenol is greater than the buckling load for Galfenol laminae sized for use in high frequency dynamic applications. In this study, prior work on stress annealing of solid rods of single and polycrystalline samples of Galfenol is successfully extended to thin laminae of Galfenol by introducing fixtures to avoid buckling of the laminae under compression during the heat treatment process. Values of the uniaxial anisotropy, cubic anisotropy, saturation magnetic induction, and saturation magnetostriction were obtained from measurements of the magnetization and magnetostriction of stress-annealed Galfenol strip as a function of compressive and tensile stress. These values were derived from fitting magnetization and magnetostriction curves to the energy expression formula [3]. Data are presented that demonstrate the magnetic uniaxial anisotropy developed by stress annealing of laminated Galfenol rods. An annealing temperature of 500 °C and a compressive stress of 200 MPa produced a uniaxial anisotropy of 11.3 kJ/m3 in this study.
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Nagel, Thomas, and Daniel J. Kelly. "Compaction and Anisotropy Induced by Remodeling of the Collagen Network’s State of Tension-Compression Transition." In ASME 2011 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2011. http://dx.doi.org/10.1115/sbc2011-53399.
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Extracellular matrix remodeling is ubiquitous in connective, musculoskeletal and cardiovascular tissues. The collagen network can thereby not only remodel its orientation [1] but also its stress-free configuration. This stress-free configuration can be described by the so-called transition stretch — the stretch above which a fiber begins to bear load. Remodeling of collagen crimp has been shown to be involved in long bone growth [2], contracture, scar pathologies, collagen gel compaction and can be cell mediated or occur via cell-independent mechanisms [3, 4, 5].
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Cornejo, S. L., J. F. Rodriguez, A. A. Valencia, A. M. Guzman, and E. A. Finol. "Flow-Induced Wall Mechanics of Patient-Specific Aneurysmal Cerebral Arteries: Nonlinear Isotropic vs. Anisotropic Wall Stress." In ASME 2008 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2008. http://dx.doi.org/10.1115/sbc2008-192626.
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There are several biomechanical factors involved in the formation, growth, remodeling, and eventual rupture of intracranial aneurysms. In particular, hemodynamic forces have a decisive role in the biomechanical environment of the aneurysmal cerebral vasculature. Most of the previous studies on vascular mechanics assessment of intracranial aneurysms are based on idealized geometries, where it has been suggested [1] that it is highly unlikely that saccular aneurysms expand due to a limit point instability. In addition, it has been reported [2] that some saccular aneurysms with non-spherical initial shape tend to become spherical when subjected to uniform pressure, because a spherical geometry is optimal to resist the pressure load, yielding a homogenous wall stress. In the present work, we present a comparison between anisotropic and isotropic constitutive models, which allows us to analyze the biomechanics of patient-specific cerebral aneurysmal arteries subjected to flow-induced pulsatile pressure. The results describe the effects of material anisotropy in the resulting wall mechanics of the intracranial vasculature geometries.
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Hart, James D., Nasir Zulfiqar, and Joe Zhou. "Evaluation of Anisotropic Pipe Steel Stress-Strain Relationships Influence on Strain Demand." In 2012 9th International Pipeline Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ipc2012-90495.
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Buried pipelines can be exposed to displacement-controlled environmental loadings (such as landslides, earthquake fault movements, etc.) which impose deformation demands on the pipeline. When analyzing pipelines for these load scenarios, the deformation demands are typically characterized based on the curvature and/or the longitudinal tension and compression strain response of the pipe. The term “strain demand” is used herein to characterize the calculated longitudinal strain response of a pipeline subject to environmentally-induced deformation demands. The shape of the pipe steel stress-strain relationship can have a significant effect on the pipe strain demands computed using pipeline deformation analyses for displacement-controlled loading conditions. In general, with sufficient levels of imposed deformation demand, a pipe steel stress-strain curve with a relatively abrupt or “sharp” elastic-to-plastic transition will tend to lead to larger strain demands than a stress-strain curve with a relatively rounded elastic-to-plastic transition. Similarly, a stress-strain curve with relatively low strain hardening modulus characteristics will tend to lead to larger strain demands than a stress-strain curve with relatively high strain hardening modulus characteristics. High strength UOE pipe can exhibit significant levels of anisotropy (i.e., the shapes of the stress-strain relationships in the longitudinal tension/compression and hoop tension/compression directions can be significantly different). To the extent that the stress-strain curves in the different directions can have unfavorable shape characteristics, it follows that anisotropy can also play an important role in pipeline strain demand evaluations. This paper summarizes a pipeline industry research project aimed at evaluation of the effects of anisotropy and the shape of pipe steel stress-strain relationships on pipeline strain demand for X80 and X100 UOE pipe. The research included: a review of pipeline industry literature on the subject matter; a discussion of pipe steel plasticity concepts for UOE pipe; characterization of the anisotropy and stress-strain curve shapes for both conventional and high strain pipe steels; development of representative analytical X80 and X100 stress-strain relationships; and evaluation of a large matrix of ground-movement induced pipeline deformation scenarios to evaluate key pipe stress-strain relationship shape and anisotropy parameters. The main conclusion from this work is that pipe steel specifications for high strength UOE pipe for strain-based design applications should be supplemented to consider shape-characterizing parameters such as the plastic complementary energy.
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Zhang, C. L., P. F. Feng, and D. Wang. "The Effect of Crystallographic Orientation on Material Removal Behavior of (001) Plane KDP Crystal in Nano-Scratch Test." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-85869.
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KDP crystal has been widely used in harmonic generation and optical parametric oscillators due to its good nonlinear optical properties and high laser damage threshold. However, because of its inherent properties, such as fragility, hygroscopic, anisotropy and low rigidity etc., KDP crystal is regarded as one of the most difficult machining materials. Nanoscratch tests were conducted in [100], [110] and [010] orientation of (001) plane KDP crystal at room temperature under a ramp loading condition from 40μN to 200 mN using with a nanomechanical test system in scratch mode to study the effects of crystallographic orientations on plastic deformation and brittle deformation features of KDP crystal. A spherical monocrystalline diamond indenter was employed in this study. Penetration depths and residual deformations of the scratch tracks were collected during the scratch process. Morphology characteristics of the scratch grooves in different scratch directions, including plastic deformation features and brittle deformation features, were observed by scanning electron microscopy. The experimental results clearly showed that there exist two distinct material deformation modes of each scratch process: plastic deformation mode, and brittle deformation mode. Comparative studies of surface depth profiles and scratch groove features induced in different crystallographic orientations revealed that the anisotropy of (001) plane KDP crystal has significant effects on the deformation features. It also presented that [110] orientation of (001) plane KDP crystal has the maximal critical load and critical depth, and can produce the highest proportion plastic deformation, which imply that [110] orientation can get adequate surface quality of KDP crystal for diamond cutting, grinding, and milling etc..
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Neupane, Sunil, Samer Adeeb, Roger Cheng, and Joe Zhou. "Modeling Approaches for Anisotropic Material Properties of High Strength Steel Pipelines and the Effect on Differential Settlement." In 2010 8th International Pipeline Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ipc2010-31206.
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High strength steel (HSS) pipelines exhibit anisotropic behavior; the yield stress in the circumferential direction is higher than the yield stress in the longitudinal direction. In addition, the shape of the stress vs. strain curve is distinctly different. The circumferential stress vs. strain curve has a sharp yield point, while there is no distinct yield point in the longitudinal direction. Most of the research done in the past on the behavior of high strength steel was based on the isotropy assumption. The material behavior of high strength steel pipelines cannot be satisfactorily modeled based on this assumption. Different material models are available which can take into account this plastic anisotropy of high strength steel. They can be grouped into two categories. First, there are models which treat material as intrinsically anisotropic [15]. And, there are other models which can take into account plastic anisotropy as being caused by the load history. In this paper, the plastic anisotropy is modeled using the second approach. Freezing and thawing of the discontinuous permafrost in the northern regions of Canada causes differential settlement of pipes. This induces significant longitudinal stress in addition to the circumferential stress due to internal pressure. It is very important to accurately model the differential settlement of the pipe and the stresses caused by it. In this paper the differential settlement is modeled using beam elements in Abaqus. The behavior of the pipeline under differential settlement loads is investigated using three different material models. The first two are assuming that the material behaves according to the traditional isotropic plasticity model, once with the longitudinal and another time using the circumferential stress strain curve as basis for the model. The third one is using an analytical virgin material stress strain curve based on the kinematic hardening plasticity model which predicts the appropriate behavior in each direction. The displacement versus the reaction force of the pipe is obtained for pipes without internal pressure and for pipes subjected to internal pressure causing a circumferential stress that is 80% of the specified minimum yield strength of the material. It is found that the response of the pipe is different for different material models. The response based on the analytical virgin material stress strain curve is closer to the response based on the longitudinal stress strain curve when the pipe is not subjected to internal pressure. But, when the pipe is subjected to internal pressure, the response using the analytical virgin material curve is closer to the circumferential stress strain curve.
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Swan, Colby C., and Hyung-Joo Kim. "Multi-Scale Micro-Mechanical Poroelastic Modeling of Fluid Flow in Cortical Bone." In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-61002.
Full textAbstract:
To explore the potential role that load-induced fluid flow plays as a mechano-transduction mechanism in bone adaptation, a lacunar-canalicular scale bone poroelasticity model is developed and exercised. The model uses micromechanics to homogenize the pericanalicular bone matrix, a system of straight circular cylinders in the bone matrix through which bone fluids can flow, as a locally anisotropic poroelastic medium. In this work, a simplified two-dimensional model of a periodic array of lacunae and their surrounding systems of canaliculi is developed and exercised to quantify local fluid flow characteristics in the vicinity of a single lacuna. When the cortical bone model is loaded, microscale stress and strain concentrations occur in the vicinity of individual lacunae and give rise to microscale spatial variations in the pore fluid pressure field. Consequently, loading of cortical bone can induce fluid flow in the canaliculi and exchange of fluid between canaliculi and lacunae. For realistic bone morphology parameters, and a range of loading frequencies, fluid pressures and fluid-solid shear stresses in the canalicular bone are computed and the associated energy dissipation in the models compared to that measured in physical in vitro experiments on human cortical bone. For realistic volume fractions of canaliculi, deformation-induced fluid flow is found to have a much larger characteristic time constant than deformation-induced flow in the Haversian system.
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Barber, Ramona B., Craig S. Hill, Pavel F. Babuska, Alberto Aliseda, Richard Wiebe, and Michael R. Motley. "Adaptive Composites for Load Control in Marine Turbine Blades." In ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/omae2017-62068.
Full textAbstract:
Marine hydrokinetic turbines typically operate in harsh, strongly dynamic conditions. All components of the turbine system must be extremely robust and able to withstand large and constantly varying loads; the long and relatively slender blades of marine turbines are especially vulnerable. Because of this, modern marine turbine blades are increasingly constructed from fiber reinforced polymer (FRP) composites. Composite materials provide superior strength- and stiffness-to-weight ratios and improved fatigue and corrosion resistance compared to traditional metallic alloys. Additionally, it is possible to tailor the anisotropic properties of FRP composites to create an adaptive pitch mechanism that will adjust the load on the turbine in order to improve system performance, especially in off-design or varying flow conditions. In this work, qualitative fundamentals of composite structures are discussed with regards to the design of experimental scale adaptive pitch blades. The load-deformation relationship of flume-scale adaptive composite blades are characterized experimentally under static loading conditions, and dynamic loading profiles during flume testing are reported. Two sets of adaptive composite blades are compared to neutral pitch composite and rigid aluminum designs. Experimental results show significant load adjustments induced through passive pitch adaptation, suggesting that adaptive pitch composite blades could be a valuable addition to marine hydrokinetic turbine technology.
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Ashrafizadeh, Hossein, Ryan Schultz, Bo Xu, and Pierre Mertiny. "Development of a Novel Technique Using Finite Element Method to Simulate Creep in Thermoplastic Fiber Reinforced Polymer Composite Pipe Structures." In ASME 2020 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/pvp2020-21529.
Full textAbstract:
Abstract High strength-to-weight ratio, excellent corrosion resistance, flexibility, superior fatigue performance, and cost competitiveness have made thermoplastic fiber reinforced polymer composites (TP-FRPCs) a material of choice for the manufacture of pipe products for use in the oil and gas industry. The TP matrix not only protects the composite structure from brittle cracking caused by dynamic loads, it also provides improved flexibility for bending of pipes to enable easier field installation and reduces the requirement for pre-fabricated bent connections. Despite the attractive mechanical performance, the design, development and qualification evaluation of TP-FRPC components for a large portion relies on experimental testing. The time and expense of manufacturing new composite prototypes and performing full-scale testing emphasizes the value of a predictive modeling. But, modeling TP-FRPC structures is not a trivial task due to their anisotropic and time-dependent properties. In this study, a new technique based on the finite element method is proposed to model anisotropic time-dependent behavior of TP-FRPCs. In the proposed technique the composite mechanical properties are captured by superimposing the properties of two fictitious materials. To that end, two overlapping three-dimensional elements with similar nodes were assigned different material properties. One of the elements is assigned to have time-dependent properties to capture the viscoelastic behavior of the matrix while the other element is given linear anisotropic properties to account for the anisotropy induced by the fiber reinforcement. The model was calibrated using data from uniaxial tensile creep tests on coupons made from pure matrix resin and uniaxial tension tests on TP-FRPC tape parallel to the fiber direction. Combined time hardening creep formulation, ANSYS 19.2 implicit analysis, and ANSYS Composite PrepPost were employed to formulate the three-dimensional finite element model. The model was validated by comparison of model predictions with experimental creep strain obtained from TP FRPC tubes with ±45° fiber layups subjected to uniaxial intermediate and high stress for 8 hours. The results obtained showed that for the tubes subjected to intermediate stress, the model predicted the creep rate in the secondary region with less than 5% error. However, for tubes subjected to high stress, the model overestimated the creep rate with over 30% error. This behavior was due to large deformation at this high level of stress and inability of the model to capture fiber realignment towards the pipe longitudinal direction and, therefore, capture an increase in stiffness. Overall, comparison of the simulation results with experimental data indicated that the technique proposed can be used as a reliable model to account for deformations caused by secondary creep in the design of TP-FRPC structures as far as deformations are relatively small and limited to a certain strain threshold. Acceptable predictions of the model, its simplicity in calibration, and limitations on available models that can simultaneously account for time-dependency and anisotropic properties, further emphasize the value of the developed model.
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Aziz, Saad, John Gale, Arya Ebrahimpour, and Marco P. Schoen. "Passive Control of a Wind Turbine Blade Using Composite Material." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-63899.
Full textAbstract:
The weight and the cost of a wind turbine are two important factors that make wind energy competitive with other energy sources. The weight of the rotor is typically 40–80% of the total weight of the system. Thus, lowering cost by reducing the weight of the blade is an important consideration. Another significant factor is the operational life of the machine. At present, a wind turbine’s life span is about 108 cycles or 20 years of continuous service. Innovative design solutions are needed in order to meet the criteria of improved stiffness, fatigue life, reliability, and efficiency. The directional property of an anisotropic composite material can be used to passively control wind turbine blade geometry in fluctuating wind speeds. Anisotropic materials show various levels of elastic coupling, based upon the ply angle in the layers. Structural behavior that exhibits both bending and twisting due to a pure bending load is known as twist-bend coupling. This type of behavior can be used for load reductions, particularly fatigue loads. The idea is to allow the blade to unload (reducing the speed) by allowing the wind induced bending moment to twist the blade. Increments in bending moment produce an increment in the twist that lowers the aerodynamically produced load. Higher blade stiffness can be achieved by full or partial replacement of glass fiber with carbon fiber. Carbon fibers are not used extensively on commercial wind turbine blades as they are more costly than glass fiber. The main objectives of this work are: (1) design a baseline model (made from glass fibers) of the wind turbine blade in accordance with published airfoil data; (2) conduct a finite element analysis of the blade and determine stresses, and strain within the blade; (3) develop a hybrid blade design by replacing the glass fibers with carbon fibers in the spar cap; and (4) validate the feasibility of implementing bend-twist coupling in the wind turbine blade by studying stresses, and strain behavior. By giving different orientation in the carbon fiber and changing the fiber layer, different designs are analyzed with regard to the above listed criteria.