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Artykuły w czasopismach na temat "Octahedral shear stress model"
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Cheng, Wangquan (Winston), i Herbert S. Cheng. "Semi-Analytical Modeling of Crack Initiation Dominant Contact Fatigue Life for Roller Bearings". Journal of Tribology 119, nr 2 (1.04.1997): 233–40. http://dx.doi.org/10.1115/1.2833163.
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The fatigue test of a needle roller bearing suggests that the dominant failure mechanism is subsurface crack initiation and propagation. Therefore, a new semi-analytical contact fatigue model is derived from a micromechanics based crack initiation model. The analysis indicates that in the life calculation the selection of the critical stress, such as the maximum orthogonal shear stress, maximum shear stress, octahedral shear stress, or von Mises equivalent stress, becomes arbitrary under the nonfrictional Hertzian line contact condition. The fatigue life of roller bearings under the pure rolling condition can be predicted by simply knowing the Hertzian contact pressure and the contact width, which avoids complicated calculation of the subsurface stresses. The film thickness, roughness, and the material hardness effects on contact fatigue are also included in the new model. The comparisons with different models and the experimental data indicate that the new model makes similar life predictions as the Ioannides-Harris model, but the new model is much simpler to use. The Lundberg-Palmgren model does not fit with the experiment data.
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Carcione, J. M., F. Poletto, B. Farina i A. Craglietto. "Simulation of seismic waves at the Earth crust (brittle-ductile transition) based on the Burgers model". Solid Earth Discussions 6, nr 1 (11.06.2014): 1371–400. http://dx.doi.org/10.5194/sed-6-1371-2014.
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Abstract. The Earth crust presents two dissimilar rheological behaviours depending on the in-situ stress-temperature conditions. The upper, cooler, part is brittle while deeper zones are ductile. Seismic waves may reveal the presence of the transition but a proper characterization is required. We first obtain a stress–strain relation including the effects of shear seismic attenuation and ductility due to shear deformations and plastic flow. The anelastic behaviour is based on the Burgers mechanical model to describe the effects of seismic attenuation and steady-state creep flow. The shear Lamé constant of the brittle and ductile media depends on the in-situ stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. The P- and S-wave velocities decrease as depth and temperature increase due to the geothermal gradient, an effect which is more pronounced for shear waves. We then obtain the P-S and SH equations of motion recast in the velocity-stress formulation, including memory variables to avoid the computation of time convolutions. The equations correspond to isotropic anelastic and inhomogeneous media and are solved by a direct grid method based on the Runge–Kutta time stepping technique and the Fourier pseudospectral method. The algorithm is tested with success against known analytical solutions for different shear viscosities. A realistic example illustrates the computation of surface and reverse-VSP synthetic seismograms in the presence of an abrupt brittle-ductile transition.
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Carcione, J. M., F. Poletto, B. Farina i A. Craglietto. "Simulation of seismic waves at the earth's crust (brittle–ductile transition) based on the Burgers model". Solid Earth 5, nr 2 (25.09.2014): 1001–10. http://dx.doi.org/10.5194/se-5-1001-2014.
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Abstract. The earth's crust presents two dissimilar rheological behaviors depending on the in situ stress-temperature conditions. The upper, cooler part is brittle, while deeper zones are ductile. Seismic waves may reveal the presence of the transition but a proper characterization is required. We first obtain a stress–strain relation, including the effects of shear seismic attenuation and ductility due to shear deformations and plastic flow. The anelastic behavior is based on the Burgers mechanical model to describe the effects of seismic attenuation and steady-state creep flow. The shear Lamé constant of the brittle and ductile media depends on the in situ stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. The P and S wave velocities decrease as depth and temperature increase due to the geothermal gradient, an effect which is more pronounced for shear waves. We then obtain the P−S and SH equations of motion recast in the velocity-stress formulation, including memory variables to avoid the computation of time convolutions. The equations correspond to isotropic anelastic and inhomogeneous media and are solved by a direct grid method based on the Runge–Kutta time stepping technique and the Fourier pseudospectral method. The algorithm is tested with success against known analytical solutions for different shear viscosities. A realistic example illustrates the computation of surface and reverse-VSP synthetic seismograms in the presence of an abrupt brittle–ductile transition.
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Ivanova, Olga, Irina Kireeva i Yuri Chumlyakov. "Modeling of Orientation Dependence of Critical Resolved Shear Stress and Deformation Mechanisms on Yield Point of Austenitic Stainless Steels Hardened by Interstitial and Substitution Atoms". Advanced Materials Research 1013 (październik 2014): 264–71. http://dx.doi.org/10.4028/www.scientific.net/amr.1013.264.
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The proposed dislocation model describes the orientation dependence of the critical resolved shear stress (CRSS) and deformation mechanisms on the yield point in single crystals of austenitic stainless steel with nitrogen impurities. The model takes into account the following: the change of the interstitial atom position in the lattice from octahedral interstice to tetrahedral site owing to passage of a leading Shockley’s partial dislocation; the change in the separation width between two partial dislocation in external stress field; the relationship between the width of the extended dislocation and the elastic interaction of the extended dislocation with the impurity atoms.
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Mousavi, S. Hamed, Mohammed A. Gabr i Roy H. Borden. "Subgrade resilient modulus prediction using light-weight deflectometer data". Canadian Geotechnical Journal 54, nr 3 (marzec 2017): 304–12. http://dx.doi.org/10.1139/cgj-2016-0062.
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Resilient modulus has been used for decades as an important parameter in pavement structure design. Resilient modulus, like other elasticity moduli, increases with increasing confining stress and decreases with increasing deviatoric stress. Several constitutive models have been proposed in the literature to calculate resilient modulus as a function of stress state. The most recent model, recommended by the Mechanistic–empirical pavement design guide (MEPDG) and used in this paper, calculates resilient modulus as a function of bulk stress, octahedral shear stress, and three fitting coefficients: k1, k2, and k3. Work in this paper presents a novel approach for predicting resilient modulus of subgrade soils at various stress levels based on light-weight deflectometer (LWD) data. The proposed model predicts the MEPDG resilient modulus model coefficients (k1, k2, and k3) directly from the ratio of applied stress to surface deflection measured during LWD testing. The proposed model eliminates uncertainties associated with needed input parameters for surface modulus (ELWD) calculation, such as the selection of an appropriate value of Poisson’s ratio for the soil layer and shape factor. The proposed model was validated with independent data from other studies reported in the literature.
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Qian, Junfeng, Yongsheng Yao, Jue Li, Hongbin Xiao i Shenping Luo. "Resilient Properties of Soil-Rock Mixture Materials: Preliminary Investigation of the Effect of Composition and Structure". Materials 13, nr 7 (3.04.2020): 1658. http://dx.doi.org/10.3390/ma13071658.
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The physical composition and stress state of soil-rock mixture (SRM) materials have a crucial influence on their mechanical properties, and play a vital role in improving the performance of subgrade. To reveal the resilient behavior and mesostructure evolution of SRM materials, triaxial tests and discrete element method (DEM) numerical analysis have been carried out. In the triaxial test section, the mechanical response of SRM materials was investigated by preparing samples under different stress states and physical states and conducting triaxial tests on samples. Simultaneously, a new irregular particle modeling method was developed and applied to the discrete element modeling process to analyze the mesostructure evolution of SRM materials under cycling loading. First, a cyclic triaxial test of SRM material is performed on the SRM material, and the effects of bulk stress, octahedral shear stress and rock content on the resilient modulus of the SRM material are analyzed. It is revealed that the resilient modulus increases with increasing bulk stress and rock content, and decreases with increasing octahedral shear stress. Based on a new resilient modulus prediction model, the relationships among the rock content, stress state and resilient modulus are established. Then, based on an improved DEM modeling method, a discrete element model of the SRM is established, and the influence of rock content on coordination number and mesostructure evolution of the SRM is analyzed. The results show that in SRM materials, the increase of crushed rock changes the mesostructure of the SRM material. With the increase of rock content, the internal contact force changes from “between soil and rock” to “between rocks”, and the skeleton formed in the rocks gradually develops overall stiffness. Under the condition of low stress, the anisotropy of the SRM material is mainly caused by the shape and grade distribution of crushed rock. The induced anisotropy caused by the change of stress state has little effect on its mechanical behavior, which may lead to the greater dispersion of multiple SRM test results.
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Tamošiūnas, Tadas, i Šarūnas Skuodis. "Predictive Stress Modeling of Resilient Modulus in Sandy Subgrade Soils". Infrastructures 8, nr 2 (8.02.2023): 29. http://dx.doi.org/10.3390/infrastructures8020029.
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The mechanical properties of pavement materials are crucial to the design and performance of flexible pavements. One of the most commonly used measures of these properties is the resilient modulus (Er). Many different models were developed to predict the resilient modulus of coarse soils, which are based on the states of stresses and the physical and mechanical properties of the soil. The unconsolidated unsaturated drained cyclic triaxial tests were performed for three variously graded and three well-graded sand specimens to determine the resilient modulus, and to perform predictive modeling using the K-θ, Rahim and George, Uzan, and Universal Witczak models. Obtained Er values directly depended on the confining pressure and deviatoric stress values used during the test. The Octahedral Shear Stress (OSS) model, proposed by the authors of the paper, predicts the resilient modulus with a coefficient of determination (R2) ranging from 0.85 to 0.99. The advantage of the model is the use of small-scale data tables, meaning fixed K1 and K2 regression coefficients, and it can be assigned to a specific specimen type without the need to determine them using the specific deviatoric and confining stresses.
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Zhang, Yongping, Shuai Peng, Xiaoqing Du, Zhenpeng Yu, Jie Wu, Xinghua Xie i Yanli Hu. "Experimental Study and Theoretical Analysis on the Compression–Shear Multiaxial Mechanical Properties of Recycled Concrete". Materials 15, nr 14 (10.07.2022): 4810. http://dx.doi.org/10.3390/ma15144810.
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Recycled concrete, which is formed by replacing coarse aggregates in ordinary concrete with recycled aggregates (RA), is of great significance for the secondary utilization of waste building resources. In civil engineering, concrete structures are sometimes subjected to a compression–shear multiaxial stress state. Therefore, research on the compression–shear multiaxial mechanical properties of recycled concrete plays an important role in engineering practice. To explore the effect of RA replacement rate on the compression–shear properties of recycled concrete, an experimental study was carried out using a compression–shear testing machine and considering five RA replacement rates and five axial compression ratios. Consequently, the failure modes and mechanical property parameters under different working conditions were obtained and were used to analyze the effects of RA replacement rate and axial compression ratio on the shear stress of recycled concrete. Eventually, the following conclusions were reached: With the growth of axial compression ratio, the shear cracks exhibit a developing trend along the oblique direction, and the friction traces on the shear surface are gradually deepened. As the replacement rate increases, the number of shear cracks is gradually increased, accompanied by increasing broken fragments falling off from the shear interface. Since the action of the axial compression ratio can effectively improve the mechanical bite force and friction on the shear interface of recycled concrete, as the axial compression ratio increases, the shear stress is gradually increased. On the other hand, due to the initial damage of RA and its weak adhesion with cement mortar, the shear stress is gradually reduced with the increase of RA replacement rate. Meanwhile, the increase in shear stress shows a gradually decreasing trend with the growth of axial compression ratio. Specifically, for the RA replacement rates of 0% and 100%, the shear stress increased by 4.06 times and 3.21 times, respectively, under the influence of the axial compression ratio. Under different axial compression ratios, the shear stress was reduced by 43~46%, due to the increase of RA replacement rate. In addition, based on the octahedral stress space and the principal stress space, a compression–shear multiaxial failure criterion and shear stress calculation model for recycled concrete were proposed, by considering the effect of the RA replacement rate. The outcomes of this research are of great significance for engineering applications and the development of recycled concrete.
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KOLCHUNOV, VL I. "DEFORMATION MODEL OF REINFORCED CONCRETE STRUCTURES' RESISTANCE - FROM DISLOCATIONS TO CRACKS". Building and reconstruction 104, nr 6 (2022): 22–39. http://dx.doi.org/10.33979/2073-7416-2022-104-6-22-39.
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The article provides a model of "internal stresses" for concrete matrix of reinforced concrete structures from dislocations, microcracks to macrocracks. The energy theory on the surface of the sphere and the definition of the integral for the mean square value of tangential stresses from plasticity theory are used. An alternative to the general model of the "eight" in the form of a paraboloid from the summation of the volume sectors, levels - radii for the matrix of sliding planes (including octahedral and pure shear) is developed. In the environment of different materials, the model is constructed based on the structure of crystals and dislocations from microcracks to macrocracks, and its working assumptions are formulated. The important principle for displacement (deformation) processes of summation and reduction of relaxing stresses from the stress-strain diagram of concrete is taken into account. The internal total stresses at the rupture of the "figure of eight" (of two contour rings) are obtained for combinations of tetrahedrons or layers-strips from the tangle-paraboloid. The lower boundaries of concrete micro-cracking depend on stresses (deformations), growth rate, energy in crack advancement for a prism or a standard "figure of eight". Displacements from shear, opening widths and crack development heights are obtained from the criteria and connecting parameters in a "representative" volume of concrete. As a result, the dilatation moduli for the stages of the stress-strain state of reinforced concrete are determined, and the equality for the second stage and the dual console elements from the fracture mechanics are obtained.
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KOLCHUNOV, VL I. "THE PHYSICAL ESSENCE OF CONCRETE AND REINFORCED CONCRETE RESISTANCE FROM DISLOCATIONS TO CRACKS". Building and reconstruction 102, nr 4 (2022): 15–33. http://dx.doi.org/10.33979/2073-7416-2022-102-4-15-33.
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The physical essence of resistance of concrete and reinforced concrete from dislocations, micro-cracks to macro-cracks and its experimental justification is investigated. For the "eight" structure of crystals of different materials (concrete and steel) a general model in the form of a sphere was developed. For it the summation of volume sectors, levels - radii from the matrix of sliding planes (including octahedral and pure shear) is written down. This uses an alternative to the theory of plasticity in the form of energy interpretation on the surface of the sphere and determining the integral of the mean square of the tangential stresses. It is important to obtain dislocations in the microcrack, angular and linear deformations, and displacements in a representative volume of the concrete cube. As the intensity increases, the deformation process proceeds already to the mainline cracks, where the double-concole elements of tension, compression, transverse shear and torsion (its internal parameters) are refined. Significant issues are the dilatation modulus and transverse coefficient, for which functions have been developed at the stages of the stress-strain state of concrete during the evolution of the transition from crack formation to main cracks. Concrete compression and tension diagrams for strain intensity or minimum pure shear use shear stresses. The fundamental difference of the stress diagram in the downward section is the use of the ultimate resistance of the concrete. Stress reduction in a material whose failure has a "tear-off" character is an unnatural phenomenon, and the limiting resistance of concrete at and reduction of prism strength at the i-th step is . The deformation pattern of concrete during the formation of earlier microcracks and then later main cracks is oriented along for compression or across the loading line for tensile force.
Rozprawy doktorskie na temat "Octahedral shear stress model"
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Zhang, Xuesong, i n/a. "Punching Shear Failure Analysis of Reinforced Concrete Flat Plates Using Simplified Ust Failure Criterion". Griffith University. School of Engineering, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20051104.153239.
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Failure criteria play a vital role in the numerical analysis of reinforced concrete structures. The current failure criteria can be classified into two types, namely the empirical and theoretical failure criteria. Empirical failure criteria normally lack reasonable theoretical backgrounds, while theoretical ones either involve too many parameters or ignore the effects of intermediate principal stress on the concrete strength. Based on the octahedral shear stress model and the concrete tensile strength under the state of triaxial and uniaxial stress, a new failure criterion, that is, the simplified unified strength theory (UST), is developed by simplifiing the five-parameter UST for the analysis of reinforced concrete structures. According to the simplified UST failure criterion, the concrete strength is influenced by the maximum and intermediate principal shear stresses together with the corresponding normal stresses. Moreover, the effect of hydrostatic pressure on the concrete strength is also taken into account. The failure criterion involves three concrete strengths, namely the uniaxial tensile and compressive strengths and the equal biaxial compressive strength. In the numerical analysis, a degenerated shell element with the layered approach is adopted for the simulation of concrete structures. In the layered approach, concrete is divided into several layers over the thickness of the elements and reinforcing steel is smeared into the corresponding number of layers of equivalent thickness. In each concrete layer, three-dimensional stresses are calculated at the integration points. For the material modelling, concrete is treated as isotropic material until cracking occurs. Cracked concrete is treated as an orthotropic material incorporating tension stiffening and the reduction of cracked shear stiffness. Meanwhile, the smeared craclc model is employed. The bending reinforcements and the stirrups are simulated using a trilinear material model. To verify the correctness of the simplified UST failure criterion, comparisons are made with concrete triaxial empirical results as well as with the Kupfer and the Ottosen failure criteria. Finally, the proposed failure criterion is used for the flexural analysis of simply supported reinforced concrete beams. Also conducted are the punching shear analyses of single- and multi-column-slab connections and of half-scale flat plate models. In view of its accuracy and capabilities, the simplified UST failure criterion may be used to analyse beam- and slab-type reinforced concrete structures.
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Zhang, Xuesong. "Punching Shear Failure Analysis of Reinforced Concrete Flat Plates Using Simplified Ust Failure Criterion". Thesis, Griffith University, 2003. http://hdl.handle.net/10072/365777.
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Failure criteria play a vital role in the numerical analysis of reinforced concrete structures. The current failure criteria can be classified into two types, namely the empirical and theoretical failure criteria. Empirical failure criteria normally lack reasonable theoretical backgrounds, while theoretical ones either involve too many parameters or ignore the effects of intermediate principal stress on the concrete strength. Based on the octahedral shear stress model and the concrete tensile strength under the state of triaxial and uniaxial stress, a new failure criterion, that is, the simplified unified strength theory (UST), is developed by simplifiing the five-parameter UST for the analysis of reinforced concrete structures. According to the simplified UST failure criterion, the concrete strength is influenced by the maximum and intermediate principal shear stresses together with the corresponding normal stresses. Moreover, the effect of hydrostatic pressure on the concrete strength is also taken into account. The failure criterion involves three concrete strengths, namely the uniaxial tensile and compressive strengths and the equal biaxial compressive strength. In the numerical analysis, a degenerated shell element with the layered approach is adopted for the simulation of concrete structures. In the layered approach, concrete is divided into several layers over the thickness of the elements and reinforcing steel is smeared into the corresponding number of layers of equivalent thickness. In each concrete layer, three-dimensional stresses are calculated at the integration points. For the material modelling, concrete is treated as isotropic material until cracking occurs. Cracked concrete is treated as an orthotropic material incorporating tension stiffening and the reduction of cracked shear stiffness. Meanwhile, the smeared craclc model is employed. The bending reinforcements and the stirrups are simulated using a trilinear material model. To verify the correctness of the simplified UST failure criterion, comparisons are made with concrete triaxial empirical results as well as with the Kupfer and the Ottosen failure criteria. Finally, the proposed failure criterion is used for the flexural analysis of simply supported reinforced concrete beams. Also conducted are the punching shear analyses of single- and multi-column-slab connections and of half-scale flat plate models. In view of its accuracy and capabilities, the simplified UST failure criterion may be used to analyse beam- and slab-type reinforced concrete structures.Thesis (Masters)
Master of Philosophy (MPhil)
School of Engineering
Full Text
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Yadav, Priti. "Multiscale Modelling of Proximal Femur Growth : Importance of Geometry and Influence of Load". Doctoral thesis, KTH, Strukturmekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209149.
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Longitudinal growth of long bone occurs at growth plates by a process called endochondral ossification. Endochondral ossification is affected by both biological and mechanical factors. This thesis focuses on the mechanical modulation of femoral bone growth occurring at the proximal growth plate, using mechanobiological theories reported in the literature. Finite element analysis was used to simulate bone growth. The first study analyzed the effect of subject-specific growth plate geometry over simplified growth plate geometry in numerical prediction of bone growth tendency. Subject-specific femur finite element model was constructed from magnetic resonance images of one able- bodied child. Gait kinematics and kinetics were acquired from motion analysis and analyzed further in musculoskeletal modelling to determine muscle and joint contact forces. These were used to determine loading on the femur in finite element analysis. The growth rate was computed based on a mechanobiological theory proposed by Carter and Wong, and a growth model in the principal stress direction was introduced. Our findings support the use of subject- specific geometry and of the principal stress growth direction in prediction of bone growth. The second study aimed to illustrate how different muscle groups’ activation during gait affects proximal femoral growth tendency in able-bodied children. Subject-specific femur models were used. Gait kinematics and kinetics were acquired for 3 able-bodied children, and muscle and joint contact forces were determined, similar to the first study. The contribution of different muscle groups to hip contact force was also determined. Finite element analysis was performed to compute the specific growth rate and growth direction due to individual muscle groups. The simulated growth model indicated that gait loading tends to reduce neck shaft angle and femoral anteversion during growth. The muscle groups that contributes most and least to growth rate were hip abductors and hip adductors, respectively. All muscle groups’ activation tended to reduce the neck shaft and femoral anteversion angles, except hip extensors and adductors which showed a tendency to increase the femoral anteversion. The third study’s aim was to understand the influence of different physical activities on proximal femoral growth tendency. Hip contact force orientation was varied to represent reported forces from a number of physical activities. The findings of this study showed that all studied physical activities tend to reduce the neck shaft angle and anteversion, which corresponds to the femur’s natural course during normal growth. The aim of the fourth study was to study the hypothesis that loading in the absence of physical activity, i.e. static loading, can have an adverse effect on bone growth. A subject-specific model was used and growth plate was modeled as a poroelastic material in finite element analysis. Prendergast’s indicators for bone growth was used to analyse the bone growth behavior. The results showed that tendency of bone growth rate decreases over a long duration of static loading. The study also showed that static sitting is less detrimental than static standing for predicted cartilage-to-bone differentiation likelihood, due to the lower magnitude of hip contact force. The prediction of growth using finite element analysis on experimental gait data and person- specific femur geometry, based on mechanobiological theories of bone growth, offers a biomechanical foundation for better understanding and prediction of bone growth-related deformity problems in growing children. It can ultimately help in treatment planning or physical activity guidelines in children at risk at developing a femur or hip deformity.QC 20170616
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Rouleau, Léonie. "Endothelial cell response to shear stress in an asymmetric stenosis model". Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99535.
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Endothelial cell dysfunction has been linked to atherosclerosis through their response to hemodynamic forces. Flow in stenotic vessels creates complex spatial gradients in wall shear stress. In vitro studies examining the effect of shear stress on endothelial cells have used unrealistic and simplified models, which cannot reproduce physiological conditions. Endothelial cells were grown and exposed for different times to physiological steady flow in straight dynamic control and in idealized asymmetric stenosis models. Cells subjected to 1D flow aligned with flow direction and had a spindle-like shape when compared to static controls. Endothelial cell morphology differed in the spatial wall shear stress gradient regions, being randomly oriented and of cobblestone shape. No other study to date has described this morphology in the presence of a positive wall shear stress gradient or gradient of significant shear magnitude. This technique provides a more realistic model to study endothelial cell response to spatial and temporal shear stress gradients that are present in vivo and is an important advancement towards a better understanding of the mechanisms involved in coronary artery disease.
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Tucker, Russell P. "Validating a new in vitro model for dynamic fluid shear stress mechanobiology". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:0ea8b159-5cb6-4bf0-9a60-4c580824016a.
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In vitro mechanotransduction studies, uncovering the basic science of the response of cells to mechanical forces, are essential for progress in tissue engineering and its clinical application. Many varying investigations have described a multitude of cell responses, however as the precise nature and magnitude of the stresses applied are infrequently reported and rarely validated, the experiments are often not comparable, limiting research progress. This thesis provides physical and biological validation of a widely available fluid stimulation device, a see-saw rocker, as an In vitro model for cyclic fluid shear stress mechanotransduction. This allows linkage between precisely characterised stimuli and cell monolayer response in a convenient six-well plate format. Computational fluid dynamic models of one well were analysed extensively to generate convergent, stable and consistent predictions of the cyclic fluid velocity vectors at a rocking frequency of 0.5 Hz, accounting for the free surface. Validation was provided by comparison with flow velocities measured experimentally using particle image velocimetry. Qualitative flow behaviour was matched and quantitative analysis showed good agreement at representative locations and time points. A maximum shear stress of 0.22Pa was estimated near the well edge, and time-average shear stress ranged between 0.029 and 0.068Pa, within the envelope of previous musculoskeletal In vitro fluid flow investigations. The CFD model was extended to explore changes in culture medium viscosity, rocking frequency and the robustness to position on the rocking platform. Shear stress magnitude was shown to increase almost linearly with an increase in the viscosity of culture medium. Compared with 0.5 Hz, models at 0.083 and 1:167 Hz, the operational limits of the see-saw rocker, indicated a change in shear stress patterns at the cell layer, and a reduction and increase in mean shear stress respectively. At the platform edge at 0.5 Hz, a 1.67-fold increase in time-average shear stress was identified. Extensive biological validations using human tenocytes underlined the versatility of the simple In vitro device. The application of fluid-induced shear stress at 0.5 Hz under varying regimes up to 0.714Pa caused a significant increase in secreted collagen (p < 0.05) compared to static controls. Tenocytes stimulated at a shear stress magnitude of 1.023Pa secreted significantly less collagen compared to static controls. The potential for a local maximum in the relationship between collagen secretion rate and shear stress was identified, indicating a change from anabolic to catabolic behaviour. Collagen biochemical assay results were echoed with antibody stains for proteins, where a co-localisation of connexin-32 with collagen type-I was also identified. A custom algorithm showed that four hours of fluid-induced shear stress of 0:033Pa intermittently applied to tenocytes encouraged alignment and elongation over an eight day period in comparison to static controls. Primary cilia were identified in human tenocyte cultures and bovine flexor tendon tissue; however primary cilium abrogation In vitro using chloral hydrate proved detrimental to cell viability. Collaborative investigations identified that ERK signalling and c-Fos transcription factor expression peaked after the application of 0.012Pa at 0.083 Hz for 20 minutes and anabolic collagen gene expression relative quantities increased after 48 hours of rocking at 0.083 Hz. In conclusion, validated shear stresses within a six-well plate, induced by cyclic flow from a see-saw rocker, provides an exceptional model for the In vitro study of dynamic fluid shear stress mechanobiology. Biological investigations have been linked to precise applied shear stress, creating a foundation for understanding the complex relationship between tenocytes and fluid-induced shear stress In vitro. Using this model, research is repeatable, comparable and accurately attributed to shear stress, accelerating the scientific advancement of musculoskeletal mechanobiology.
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Willett, Nick J. "Redox signaling in an in vivo flow model of low magnitude oscillatory wall shear stress". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33917.
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Atherosclerosis is a multifactoral inflammatory disease that occurs in predisposed locations in the vasculature where blood flow is disturbed. In vitro studies have implicated reactive oxygen species as mediators of mechanotransduction leading to inflammatory protein expression and ultimately atherogenesis. While these cell culture-based studies have provided enormous insight into the effects of WSS on endothelial biology, the applicability to the in vivo setting is questionable. We hypothesized that low magnitude oscillatory WSS acts through reactive oxygen species (ROS) to increase expression of inflammatory cell adhesion molecules leading to the development of atherosclerotic lesions. The overall objective for this thesis was to develop an in vivo flow model that produces low magnitude oscillatory WSS which could be used to investigate the in vivo molecular mechanisms of mechanotransduction.
We created a novel aortic coarctation model using a shape memory nitinol clip. The clip reproducibly constricts the aorta creating a narrowing of the lumen resulting in a stenosis. This mechanical constraint produces a region of flow separation downstream from the coarctation. We have characterized the coarctation in terms of the efficacy, pressure loss, and fluid dynamics. We then measured the endothelial response of shear sensitive redox and inflammatory markers. Lastly, we utilized genetically modified mice and mice treated with pharmacological inhibitors to investigate the mechanisms involved in the expression of WSS induced inflammatory and redox markers.
We found that inducing a coarctation of the aorta using a nitinol clip uniquely created a hemodynamic environment of low magnitude oscillatory WSS without a significant change in blood pressure. Using this model we found that the in vivo endothelial phenotype associated with acutely disturbed flow was characterized by increased production of superoxide and increased expression of select inflammatory proteins. In comparison, the phenotype associated with chronically disturbed flow was characterized by a more modest increase in superoxide and increased levels of multiple inflammatory proteins. We determined that in regions of acutely disturbed flow in vivo, VCAM-1 expression was not modulated by reactive oxygen species. Additionally, p47 phox-dependent NADPH Oxidase activity does not have a functional role in WSS induced superoxide generation in the endothelium.
In summary, we have created a novel murine model of low magnitude oscillatory WSS that can be used to investigate the in vivo molecular mechanisms associated with atherogenesis. While previous data obtained in vitro indicated that depletion of an individual ROS was sufficient to inhibit flow-induced inflammatory protein expression, our findings, to the contrary, showed that antioxidant treatment in vivo does not inhibit shear-dependent inflammatory protein expression. Our results suggest that atherogenesis in the in vivo environment is significantly more complicated than the in vitro environment and that parallel pathways and compensatory mechanisms are likely activated in vivo in response to WSS. These results could have significant implications in the efficacy of antioxidant treatment of atherosclerosis and could explain the complexity of results observed in clinical trials.
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Vorobtsova, Natalya. "Computational model of coronary tortuosity". Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/51267.
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Coronary tortuosity is the abnormal curving and twisting of the coronary arteries. Although the phenomenon of coronary tortuosity is frequently encountered by cardiologists its clinical significance is unclear. It is known that coronary tortuosity has significant influence on the hemodynamics inside the coronary arteries, but it is difficult to draw definite conclusions due to the lack of patient-specific studies and an absence of a clear definition of tortuosity.
In this work, in order to investigate a relation of coronary tortuosity to such diseases as atherosclerosis, ischemia, and angina, a numerical investigation of coronary tortuosity was performed. First, we studied a correlation between a degree of tortuosity and flow parameters in three simplified vessels with curvature and zero torsion. Next, a statistical analysis based on flow calculations of 23 patient-based real tortuous arteries was performed in order to investigate a correlation between tortuosity and flow parameters, such as pressure drop, wall shear stress distribution, and a strength of helical flow, represented by a helicity intensity, and concomitant risks.
Results of both idealized and patient-specific studies indicate that a risk of perfusion defects grows with an increased degree of tortuosity due to an increased pressure drop downstream an artery. According to the results of the patient-specific study, a risk of atherosclerosis decreases in more tortuous arteries - a result different from an outcome of the idealized study of arteries with zero torsion. Consequently, a modeling of coronary tortuosity should take into account all aspects of tortuosity including a heart shape that introduces additional torsion to arteries. Moreover, strength of a helical flow was shown to depend strongly on a degree of tortuosity and affect flow alterations and accompanying risks of developing atherosclerosis and perfusion defects. A corresponding quantity, helicity intensity, might have a potential to be implemented in future studies as a universal single parameter to describe tortuosity and assess congruent impact on the health of a patient.Master of Science
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Miller, Leigh Ann. "Wall shear stress distribution and the effects of branch angle on a human coronary artery model". Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/16088.
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Emmott, Alexander. "The effect of wall shear stress in a novel endothelial tissue culture model of arterial curvature". Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107873.
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Vessel wall shear stress (WSS) is hypothesized to cause focal endothelial cell (EC) dysfunction leading to a pro-inflammatory environment. Clinical observations of focal atherosclerosis have been documented in arterial bifurcations, branch points and in lesser arterial curvature. In both in vivo and in vitro experiments, it has been demonstrated that WSS can stimulate a cascade of biochemical interactions which activate the inflammatory pathway. The resultant functional changes include altered expression of inter- and vascular- cellular adhesion molecules (ICAM-1 and VCAM-1, respectively) on the luminal surface of the endothelium. This change in phenotype may indicate the early stages of lesion development by facilitating the adhesion of circulating leukocytes.We have created a three-dimensional tissue culture model using the non-dimensional Dean's number to model physiological hemodynamics in a curved artery (De=104). WSS within our tissue culture model is defined for the inner and outer walls using computational fluid dynamics to ensure well-defined stimuli. ECs cultured within the model are subjected to 24h perfusion experiments at an inlet WSS of 10 dynes/cm2. Regional changes in EC phenotype are evaluated using cell morphology (shape index), protein expression, and circulating leukocyte attachment. EC shape index suggests that ECs lining the inner wall exhibit an atheroprone phenotype relative to those seen lining the outer wall, with significance being observed throughout the entirety of the 180° curve. Similarly, leukocyte distribution favours the inner wall of the tissue culture model between 0°-90°. However, Western Blot analysis demonstrates a 54% decrease in endothelial ICAM-1 in the curve relative to the straight internal control. This study demonstrates that flow through a curved vessel results in significant regional variations in EC phenotype and preferential leukocyte adhesion in vitro, providing further insight into the role of localized hemodynamics in the early stages of atherosclerosis.Il existe une hypothèse spéculant que les variations locales des forces hémodynamiques, particulièrement la contrainte de cisaillement à la paroi (CCP), mènent à un dérèglement important des cellules endothéliales (CEs) causant un environnement pro-inflammatoire. Les observations cliniques d'athérosclérose ont été documentées principalement dans: les bifurcations artérielles, les points de branchement et à la courbure artérielle. Des expériences in vivo et in vitro ont démontré que la CCP peut engendrer une cascade d'interactions biochimiques qui finissent par activer la voie inflammatoire. Les changements fonctionnels incluent : une expression modifiée des molécules d'adhésion inter-vasculaires et-cellulaire (ICAM-1 et VCAM-1, respectivement) de la surface luminale de l'endothélium. Ce changement de phénotype peuvent aider à identifier les premières phases du développement d'une lésion en facilitant l'adhérence des leucocytes en circulation dans le sang.Nous avons créé un modèle tridimensionnel de culture cellulaire en utilisant le nombre adimensionnel de Dean pour modéliser l'hémodynamique physiologique dans une artère courbée (De = 104). La CCP au sein de notre modèle de culture cellulaire est définie par les murs intérieurs et extérieurs en utilisant une méthode de dynamique des fluides computationnelle. Les CEs cultivées dans le modèle sont soumis à des expériences de perfusion pour une durée de 24h et à une CCP a l'entrée de 10 dynes/cm2. Les changements régionaux dans le phénotype des CEs sont évaluées en utilisant des indices de morphologie cellulaire (indice de forme par exemple), l'expression de certaines protéines et l'attachement des leucocytes circulants. L'indice de forme suggère que les CEs tapissant la paroi interne de notre modèle courbé présentent un phénotype atheroprone important par rapport à ceux vus tapissant le mur extérieur observée dans l'ensemble de la courbe de 180°. De même, la distribution des leucocytes favorise le mur interne du modèle de culture cellulaire entre 0°-90°. Cependant, l'analyse Western Blot montre une réduction de 54% en concentration de protéine endothéliale ICAM-1 dans la courbe relative au contrôle interne de droites. Cette étude démontre que le flux à travers un vaisseau courbé donne des résultats avec d'importantes variations locales dans le phénotype des CEs et préférentielles d'adhérence des leucocytes in vitro, donnant un aperçu futur sur le rôle de l'hémodynamique local dans les premiers stades de l'athérosclérose.
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Wang, Taige. "Mathematical Analysis on the PEC model for Thixotropic Fluids". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/70907.
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A lot of fluids are more complex than water: polymers, paints, gels, ketchup etc., because of big particles and their complicated microstructures, for instance, molecule entanglement. Due to this structure complexity, some material can display that it is still in yielded state when the imposed stress is released. This is referred to as thixotropy. This dissertation establishes mathematical analysis on a thixotropic yield stress fluid using a viscoelastic model under the limit that the ratio of retardation time versus relaxation time approaches zero. The differential equation model (the PEC model) describing the evolution of the conformation tensor is analyzed. We model the flow when simple shearing is imposed by prescribing a total stress.
One part of this dissertation focuses on oscillatory shear stresses. In shear flow, different fluid states corresponding to yielded and unyielded phases occur. We use asymptotic analysis to study transition between these phases when slow oscillatory shearing is set up. Simulations will be used to illustrate and supplement the analysis.
Another part of the dissertation focuses on planar Poiseuille flow. Since the flow is spatially inhomogeneous in this situation, shear bands are observed. The flow is driven by a homogeneous pressure gradient, leading to a variation of stress in the cross-stream direction. In this setting, the flow would yield in different time scales during the evolution. Formulas linking the yield
locations, transition width, and yield time are obtained. When we introduce Korteweg stress in the transition, the yield location is shifted. An equal area
rule is identified to fit the shifted locations.Ph. D.
Książki na temat "Octahedral shear stress model"
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Sarkar, Sarben. Application of a Reynolds stress turbulence model to the compressible shear layer. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1990.
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Sarkar, Sutanu. Application of a Reynolds stress turbulence model to the compressible shear layer. Hampton, Va: Institute for Computer Applications in Science and Engineering, 1990.
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National Aeronautics and Space Administration (NASA) Staff. Recalibration of the Shear Stress Transport Model to Improve Calculation of Shock Separated Flows. Independently Published, 2019.
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B, Gatski T., Speziale C. G. 1948- i Institute for Computer Applications in Science and Engineering., red. On the prediction of free turbulent jets with swirl using a quadratic pressure-strain model. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, Institute for Computer Applications in Science and Engineering, 1994.
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B, Gatski T., Speziale C. G. 1948- i Institute for Computer Applications in Science and Engineering., red. On the prediction of free turbulent jets with swirl using a quadratic pressure-strain model. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, Institute for Computer Applications in Science and Engineering, 1994.
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Pankaj, Goel, i United States. National Aeronautics and Space Administration, red. Third-moment closure of turbulence for predictions of separating and reattaching shear flows: Final report on "A study of Reynolds-Stress Closure Model". [Washington, D.C.]: National Aeronautics and Space Administration, 1986.
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Pankaj, Goel, i United States. National Aeronautics and Space Administration, red. Third-moment closure of turbulence for predictions of separating and reattaching shear flows: Final report on "A study of Reynolds-Stress Closure Model". [Washington, D.C.]: National Aeronautics and Space Administration, 1986.
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New Hypothesis on the Anisotropic Reynolds Stress Tensor for Turbulent Flows : Volume II: Practical Implementation and Applications of an Anisotropic Hybrid K-Omega Shear-Stress Transport/Stochastic Turbulence Model. Springer International Publishing AG, 2020.
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Könözsy, László. New Hypothesis on the Anisotropic Reynolds Stress Tensor for Turbulent Flows : Volume II: Practical Implementation and Applications of an Anisotropic Hybrid K-Omega Shear-Stress Transport/Stochastic Turbulence Model. Springer International Publishing AG, 2021.
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Cates, M. Complex fluids: the physics of emulsions. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198789352.003.0010.
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These lectures start with the mean field theory for a symmetric binary fluid mixture, addressing interfacial tension, the stress tensor, and the equations of motion (Model H). We then consider the phase separation kinetics of such a mixture: coalescence, Ostwald ripening, its prevention by trapped species, coarsening of bicontinuous states, and the role of shear flow. The third topic addressed is the stabilization of emulsions by using surfactants to reduce or even eliminate the interfacial tension between phases; the physics of bending energy, which becomes relevant in the latter case, is then presented briefly. The final topic is the creation of long-lived metastable emulsions by adsorption of colloidal particles or nanoparticles at the fluid–fluid interface; alongside spherical droplets, these methods can be used to create a range of unconventional structures with potentially interesting properties that are only now being explored.
Części książek na temat "Octahedral shear stress model"
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Janicka, J., i W. Kollmann. "Reynolds-Stress Closure Model for Conditional Variables". W Turbulent Shear Flows 4, 73–86. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/978-3-642-69996-2_6.
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Lu, Yingfa, i Kai Cui. "Shear–Stress Constitutive Model and Its Parameter Calibration". W Proceedings of GeoShanghai 2018 International Conference: Fundamentals of Soil Behaviours, 42–54. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-13-0125-4_5.
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Wei, Wang, Lu Tinghao i Ji Litong. "Study on Shear Stress-Strain Model for Unsaturated Soil". W Thermo-Hydromechanical and Chemical Coupling in Geomaterials and Applications, 85–92. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2013. http://dx.doi.org/10.1002/9781118623565.ch6.
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Jia, Zhe, Lei Mu, Ben Guan i Yong Zang. "An Extended Ductile Fracture Prediction Model Considering Hydrostatic Stress and Maximum Shear Stress". W Forming the Future, 1595–603. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-75381-8_133.
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Könözsy, László. "The k- $$\omega $$ ω Shear-Stress Transport (SST) Turbulence Model". W A New Hypothesis on the Anisotropic Reynolds Stress Tensor for Turbulent Flows, 57–66. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-13543-0_3.
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Wang, Wei, Ting Hao Lu i Bin Xiang Sun. "Mathematical Model for Shear Stress-Strain Relationship of Soil-Concrete Interface during Shear Fracture Process". W Advances in Fracture and Damage Mechanics VI, 881–84. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-448-0.881.
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Bahiuddin, Irfan, Abdul Yasser Abd Fatah, Saiful Amri Mazlan, Fitrian Imaduddin, Mohd Hatta Mohammed Ariff, Dewi Utami i Nurhazimah Nazmi. "Extreme Learning Machine Based-Shear Stress Model of Magnetorheological Fluid for a Valve Design". W Proceedings of the 6th International Conference and Exhibition on Sustainable Energy and Advanced Materials, 275–84. Singapore: Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-15-4481-1_27.
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Teymur, B., i S. P. G. Madabhushi. "Shear Stress-Strain Analysis of Sand in ESB Model Container by Harmonic Wavelet Techniques". W Physical Modelling in Geotechnics, 201–6. London: Routledge, 2022. http://dx.doi.org/10.1201/9780203743362-36.
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Radhakrishnan, Sarath, Lawrence Adu Gyamfi, Arnau Miró, Bernat Font, Joan Calafell i Oriol Lehmkuhl. "A Data-Driven Wall-Shear Stress Model for LES Using Gradient Boosted Decision Trees". W Lecture Notes in Computer Science, 105–21. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-90539-2_7.
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Noor, Mohd Jamaludin. "Anisotropic and elastic–plastic rock deformation model for accurate prediction of intact rock stress–strain response". W Soil Settlement and the Concept of Effective Stress and Shear Strength Interaction, 197–232. First edition. | Boca Raton : CRC Press, 2020.: CRC Press, 2020. http://dx.doi.org/10.1201/9781003121503-6.
Pełny tekst źródłaStreszczenia konferencji na temat "Octahedral shear stress model"
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Ellyin, F., Y. Hu i Z. Xia. "Multiaxial Behavior and Viscoelastic Constitutive Modeling of Epoxy Polymers". W ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1192.
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Abstract A nonlinear viscoelastic constitutive model previously proposed has been modified to account for hydrostatic stress influence. The modification is achieved by incorporating the hydrostatic stress in the equivalent stress definition. The present model predicts a shift of stress envelopes along equibiaxial compressive stress direction. It also predicts different octahedral shear stress versus octahedral shear strain curves for various strain paths. These trends indicate improved agreement between the model prediction and multiaxial experiment data.
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Telesman, Jack, i Louis J. Ghosn. "Fatigue Crack Growth Behavior of PWA 1484 Single Crystal Superalloy at Elevated Temperatures". W ASME 1995 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1995. http://dx.doi.org/10.1115/95-gt-452.
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A study was done to determine the fatigue crack growth behavior of a PWA 1484 single crystal nickel base superalloy in a temperature range of 427°C to 871°C. Two distinctive failure modes were observed which were a function of both temperature and frequency. At lower temperatures and higher frequencies crack growth occured on the {111} octahedral slip planes at an oblique angle to the loading direction. Higher temperatures and decrease in frequencies favored a Mode I type failure process. The failure mode transitions were explained by invoking arguments based on environmental damage mechanisms. The fatigue crack growth rate data were analyzed using three different crack driving force parameters. The parameters investigated consisted of the Mode I stress intensity parameter corrected for the inclined crack trajectory, and two different octahedral Mode II parameters which are based on the calculation of resolved shear stresses on the {111} slip systems. The Mode I ΔK parameter did a fair job in correlating the data but did not collapse it into a single narrow band. The two octahedral crack driving force parameters, ΔKRSS and a newly proposed ΔKOCT, collapsed all the data into a single narrow band. In addition to correlating the fatigue crack growth rates, the two octahedral parameters also predicted the {111} planes on which the crack growth took place.
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Siddiqui, Shadab, Nagaraj K. Arakere i Fereshteh Ebrahimi. "Effect of Temperature and Crystal Orientation on the Plasticity (SLIP) Evolution in Single Crystal Nickel Base Superalloy Notched Specimens". W ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27095.
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A comprehensive numerical investigation of plasticity (slip) evolution near notches was conducted at 28°C and 927°C, for two crystallographic orientations of double-notched single crystal nickel base superalloys (SCNBS) specimens. The two specimens have a common loading orientation of <001> and have notches parallel to the <010> (specimen I) and <110> (specimen II) orientation, respectively. A three dimensional anisotropic linear elastic finite element model was employed to calculate the stress field near the notch of these samples. Resolved shear stress values were obtained near the notch for the primary octahedral slip systems ({111} <110>) and cube slip systems ({100} <110>). The effect of temperature was incorporated in the model as changes in the elastic modulus values and the critical resolved shear stress (CRSS). The results suggest that the number of dominant slip systems (slip systems with the highest resolved shear stress) and the size and the shape of the plastic zones around the notch are both functions of the orientation as well as the test temperature. A comparison between the absolute values of resolved shear stresses near the notch at 28°C and 927°C on the {111} slip planes revealed that the plastic zone size and the number of activated dominant slip systems are not significantly affected by the temperature dependency of the elastic properties of the SCNBS, but rather by the change in critical resolved shear stress of this material with temperature. The load required to initiate slip was found to be lower in specimen II than in specimen I at both temperatures. Furthermore, at 927°C the maximum resolved shear stress (RSS) on the notch surface was found to be greater on the {100} slip planes as compared with the {111} slip planes in both specimens. The results from this study will be helpful in understanding the slip evolution in SCNBS at high temperatures.
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Arakere, Nagaraj K., Erik C. Knudsen, Gregory R. Swanson, Gregory Duke i Gilda Ham-Battista. "Subsurface Stress Fields in FCC Single Crystal Anisotropic Contacts". W ASME Turbo Expo 2004: Power for Land, Sea, and Air. ASMEDC, 2004. http://dx.doi.org/10.1115/gt2004-53913.
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Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent high cycle fatigue (HCF) failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is presented for evaluating the subsurface stresses in the elastic half-space, based on the adaptation of a stress function method outlined by Lekhnitskii [1]. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis (FEA). Effects of crystal orientation on stress response and fatigue life are examined. Obtaining accurate subsurface stress results for anisotropic single crystal contact problems require extremely refined three-dimensional (3-D) finite element grids, especially in the edge of contact region. Obtaining resolved shear stresses (RSS) on the principal slip planes also involves considerable post-processing work. For these reasons it is very advantageous to develop analytical solution schemes for subsurface stresses, whenever possible.
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Arakere, Nagaraj K., i Gregory Swanson. "Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys". W ASME Turbo Expo 2000: Power for Land, Sea, and Air. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/2000-gt-0334.
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High Cycle Fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Single crystal nickel turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry because of their superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493, PWA 1484, RENE’ N-5 and CMSX-4. These alloys play an important role in commercial, military and space propulsion systems. Single crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades are complicated to predict due to the material orthotropy and variations in crystal orientations. Fatigue life estimation of single crystal turbine blades represents an important aspect of durability assessment. It is therefore of practical interest to develop effective fatigue failure criteria for single crystal nickel alloys and to investigate the effects of variation of primary and secondary crystal orientation on fatigue life. A fatigue failure criterion based on the maximum shear stress amplitude [Δτmax] on the 24 octahedral and 6 cube slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criterion reduces the scatter in uniaxial LCF test data considerably for PWA 1493 at 1200F in air. Additionally, single crystal turbine blades used in the alternate advanced high-pressure fuel turbopump (AHPFTP/AT) are modeled using a large-scale 3D finite element (FE) model. This FE model is capable of accounting for material orthotrophy and variation in primary and secondary crystal orientation. Effects of variation in crystal orientation on blade stress response are studied based on 297 FE model runs. Fatigue lives at critical points in the blade are computed using FE stress results and the failure criterion developed. Stress analysis results in the blade attachment region are also presented. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to significantly increase a component’s resistance to fatigue crack growth without adding additional weight or cost.
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BARTON, J., R. RUBINSTEIN i K. KIRTLEY. "Nonlinear Reynolds stress model for turbulent shear flows". W 29th Aerospace Sciences Meeting. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1991. http://dx.doi.org/10.2514/6.1991-609.
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Gomez, Carlos, i Sharath Girimaji. "Algebraic Reynolds Stress Model (ARSM) for Compressible Shear Flows". W 41st AIAA Fluid Dynamics Conference and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2011. http://dx.doi.org/10.2514/6.2011-3572.
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Chen, Gao-Feng, Chen Deng-Hong, Shen-Wei Huang i Ying-Fa Lu. "Study on Shear Strength Tests and Uniformed Constitutive Model of Shear Stress-Shear Displacement for Unsaturated Soils". W GeoHunan International Conference 2011. Reston, VA: American Society of Civil Engineers, 2011. http://dx.doi.org/10.1061/47633(412)11.
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Wang, Wei, i Tinghao Lu. "Mathematical Model for Shear Stress-strain Relationship of Unsaturated Soil". W 2008 International Workshop on Modelling, Simulation and Optimization. IEEE, 2008. http://dx.doi.org/10.1109/wmso.2008.104.
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Balasubramanian, Ravishankar, Sean Barrows i Jen Chen. "Investigation of Shear-Stress Transport Turbulence Model for Turbomachinery Applications". W 46th AIAA Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2008. http://dx.doi.org/10.2514/6.2008-566.
Pełny tekst źródłaRaporty organizacyjne na temat "Octahedral shear stress model"
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Kinikles, Dellena, i John McCartney. Hyperbolic Hydro-mechanical Model for Seismic Compression Prediction of Unsaturated Soils in the Funicular Regime. Pacific Earthquake Engineering Research Center, University of California, Berkeley, CA, grudzień 2022. http://dx.doi.org/10.55461/yunw7668.
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A semi-empirical elasto-plastic constitutive model with a hyperbolic stress-strain curve was developed with the goal of predicting the seismic compression of unsaturated sands in the funicular regime of the soil-water retention curve (SWRC) during undrained cyclic shearing. Using a flow rule derived from energy considerations, the evolution in plastic volumetric strain (seismic compression) was predicted from the plastic shear strains of the hysteretic hyperbolic stress-strain curve. The plastic volumetric strains are used to predict the changes in degree of saturation from phase relationships and changes in pore air pressure from Boyle’s and Henry’s laws. The degree of saturation was used to estimate changes in matric suction from the transient scanning paths of the SWRC. Changes in small-strain shear modulus estimated from changes in mean effective stress computed from the constant total stress and changes in pore air pressure, degree of saturation and matric suction, in turn affect the hyperbolic stress-strain curve’s shape and the evolution in plastic volumetric strain. The model was calibrated using experimental shear stress-strain backbone curves from drained cyclic simple shear tests and transient SWRC scanning path measurements from undrained cyclic simple shear tests. Then the model predictions were validated using experimental data from undrained cyclic simple shear tests on unsaturated sand specimens with different initial degrees of saturation in the funicular regime. While the model captured the coupled evolution in hydro-mechanical variables (pore air pressure, pore water pressure, matric suction, degree of saturation, volumetric strain, effective stress, shear modulus) well over the first 15 cycles of shearing, the predictions were less accurate after continued cyclic shearing up to 200 cycles. After large numbers of cycles of undrained shearing, a linear decreasing trend between seismic compression and initial degree of saturation was predicted from the model while a nonlinear increasing-decreasing trend was observed in the cyclic simple shear experiments. This discrepancy may be due to not considering post shearing reconsolidation in the model, calibration of model parameters, or experimental issues including a drift in the position of the hysteretic shear-stress strain curve. Nonetheless, the trend from the model is consistent with predictions from previously- developed empirical models in the funicular regime of the SWRC. The developments of the new mechanistic model developed in this study will play a key role in the future development of a holistic model for predicting the seismic compression across all regimes of the SWRC.
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Pullammanappallil, Pratap, Haim Kalman i Jennifer Curtis. Investigation of particulate flow behavior in a continuous, high solids, leach-bed biogasification system. United States Department of Agriculture, styczeń 2015. http://dx.doi.org/10.32747/2015.7600038.bard.
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Recent concerns regarding global warming and energy security have accelerated research and developmental efforts to produce biofuels from agricultural and forestry residues, and energy crops. Anaerobic digestion is a promising process for producing biogas-biofuel from biomass feedstocks. However, there is a need for new reactor designs and operating considerations to process fibrous biomass feedstocks. In this research project, the multiphase flow behavior of biomass particles was investigated. The objective was accomplished through both simulation and experimentation. The simulations included both particle-level and bulk flow simulations. Successful computational fluid dynamics (CFD) simulation of multiphase flow in the digester is dependent on the accuracy of constitutive models which describe (1) the particle phase stress due to particle interactions, (2) the particle phase dissipation due to inelastic interactions between particles and (3) the drag force between the fibres and the digester fluid. Discrete Element Method (DEM) simulations of Homogeneous Cooling Systems (HCS) were used to develop a particle phase dissipation rate model for non-spherical particle systems that was incorporated in a two-fluid CFDmultiphase flow model framework. Two types of frictionless, elongated particle models were compared in the HCS simulations: glued-sphere and true cylinder. A new model for drag for elongated fibres was developed which depends on Reynolds number, solids fraction, and fibre aspect ratio. Schulze shear test results could be used to calibrate particle-particle friction for DEM simulations. Several experimental measurements were taken for biomass particles like olive pulp, orange peels, wheat straw, semolina, and wheat grains. Using a compression tester, the breakage force, breakage energy, yield force, elastic stiffness and Young’s modulus were measured. Measurements were made in a shear tester to determine unconfined yield stress, major principal stress, effective angle of internal friction and internal friction angle. A liquid fludized bed system was used to determine critical velocity of fluidization for these materials. Transport measurements for pneumatic conveying were also assessed. Anaerobic digestion experiments were conducted using orange peel waste, olive pulp and wheat straw. Orange peel waste and olive pulp could be anaerobically digested to produce high methane yields. Wheat straw was not digestible. In a packed bed reactor, anaerobic digestion was not initiated above bulk densities of 100 kg/m³ for peel waste and 75 kg/m³ for olive pulp. Interestingly, after the digestion has been initiated and balanced methanogenesis established, the decomposing biomass could be packed to higher densities and successfully digested. These observations provided useful insights for high throughput reactor designs. Another outcome from this project was the development of low cost devices to measure methane content of biogas for off-line (US$37), field (US$50), and online (US$107) applications.
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STRESS RESPONSE AND INITIAL STIFFNESS OF SIDE PLATE CONNECTIONS TO WCFT COLUMNS. The Hong Kong Institute of Steel Construction, wrzesień 2021. http://dx.doi.org/10.18057/ijasc.2021.17.3.9.
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To study the mechanism of load transfer in double-side-plate connections between I-beams and wall-type concrete-filled steel tubular columns, a pseudo-static experiment and finite element analysis were conducted for two full-scaled specimens. The results revealed that the primary load was transmitted along an S-shaped path in the side plate, and the primary strain occurred in an X-shaped region between the left and right steel beam flanges. The shear force in the steel beam web was transmitted first to the side plate centre and then to the joint area, where the side plate, steel tube web, and concrete all resisted the internal force. Based on principal component methods, a calculation formula was established for initial rotational stiffness that comprehensively considers the influence of the tensions, compression, and shear deformation of the cover plate, side plate, and web. Comparing this formula with an existing model showed that the proposed formula is suitable for new types of side plate joints. Moreover, it can accurately calculate the initial rotational stiffness of the joint, thus providing a reliable basis for future engineering design.
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AXIAL COMPRESSION BEHAVIOR OF SQUARE THIN-WALLED CFST COLUMN TO RC BEAM JOINTS. The Hong Kong Institute of Steel Construction, sierpień 2022. http://dx.doi.org/10.18057/icass2020.p.288.
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To investigate the influence of eccentricity ratio and slenderness ratio on the mechanical properties of eccentric compressed concrete filled steel tubular (CFST) lattice column, the ultimate bearing capacity tests of 20 K shape arrangement lacing strip of four-tube CFST columns were conducted. Based on the stress-strain relationship of CFST and the influence of shear deformation, the equilibrium equation of the mid-section is established and a numerical method for the ultimate bearing capacity of CFST lattice column is proposed. The slenderness reduction coefficient calculation model and equivalent slenderness ratio formula of CFST lattice column are established. Combined with the numerical results and the slenderness ratio reduction coefficient calculation model, the formula of slenderness ratio reduction coefficient is put forward. The comparison between theoretical analysis and experimental results shows that the calculation method of elastic-plastic ultimate bearing capacity of CFST lattice column proposed in this paper is quite accurate. The research outcomes can provide a reference for the application of CFST lattice column and revision of current specifications.
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CALCULATION METHOD OF ULTIMATE LOAD BEARING CAPACITY OF CONCRETE FILLED STEEL TUBULAR LATTICE COLUMNS. The Hong Kong Institute of Steel Construction, sierpień 2022. http://dx.doi.org/10.18057/icass2020.p.095.
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To investigate the influence of eccentricity ratio and slenderness ratio on the mechanical properties of eccentric compressed concrete filled steel tubular (CFST) lattice column, the ultimate bearing capacity tests of 20 K shape arrangement lacing strip of four-tube CFST columns were conducted. Based on the stress-strain relationship of CFST and the influence of shear deformation, the equilibrium equation of the mid-section is established and a numerical method for the ultimate bearing capacity of CFST lattice column is proposed. The slenderness reduction coefficient calculation model and equivalent slenderness ratio formula of CFST lattice column are established. Combined with the numerical results and the slenderness ratio reduction coefficient calculation model, the formula of slenderness ratio reduction coefficient is put forward. The comparison between theoretical analysis and experimental results shows that the calculation method of elastic-plastic ultimate bearing capacity of CFST lattice column proposed in this paper is quite accurate. The research outcomes can provide a reference for the application of CFST lattice column and revision of current specifications.