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R C Batra - One of the best experts on this subject based on the ideXlab platform.
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free vibration of bi directional functionally graded material circular beams using shear deformation theory employing logarithmic function of radius
Composite Structures, 2019Co-Authors: Jamshid Fariborz, R C BatraAbstract:Abstract Curved beams such as arches find ubiquitous applications in civil, mechanical and aerospace engineering , e.g., stiffened floors, fuselage , railway compartments, and wind turbine blades. The analysis of free vibrations of curved structures plays a critical role in their design to avoid transient loads with dominant frequencies close to their natural frequencies. One way to increase their applications and possibly make them lighter without sacrificing strength is to comprise them of Functionally Graded Materials (FGMs) that are composites with continuously varying material properties in one or more directions. Here, we study free vibrations of FGM circular beams by using a shear deformation theory that incorporates through-the-thickness logarithmic variation of the Circumferential Displacement , does not require a shear correction factor , and has a parabolic through-the-thickness distribution of the shear strain. The radial Displacement of a point is assumed to depend only upon its angular position. Thus the beam theory generalizes the Timoshenko beam theory. Equations governing transient deformations of the beam are derived by using Hamilton’s principle. Assuming a time harmonic variation of Displacements, and by utilizing a generalized differential quadrature method (GDQM), the free vibration problem is reduced to solving an algebraic eigenvalue problem whose solution provides frequencies and corresponding mode shapes. Results are presented for different spatial variations of the material properties, boundary conditions, and the beam aspect ratio. It is found that frequencies of the FGM beam are bounded by those of two geometrically identical homogeneous beams composed of the two constituents of the beam. Keeping other variables fixed, the change in the beam opening angle results in very close frequencies of the first two modes of vibration at a critical value of the opening angle, a phenomenon usually called mode transition. The critical opening angle is essentially the same for radially graded, bidirectionally graded and monolithic beams. It equals about 80° (60°) for clamped-clamped (hinged-hinged) beams.
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shear deformation theory using logarithmic function for thick circular beams and analytical solution for bi directional functionally graded circular beams
Composite Structures, 2017Co-Authors: Anup Pydah, R C BatraAbstract:A shear deformation theory including a logarithmic function in the postulated expression for the Circumferential Displacement is developed for thick circular beams and is used to analytically solve static deformations of bi-directional functionally graded circular beams. The consideration of a logarithmic term is motivated by the Displacement field in the analytical solution of the plane strain elasticity problem of a hollow circular cylindrical shell. The non-zero shear traction boundary conditions at the two major surfaces of the beam are a priori satisfied by the assumed Displacement field. The material properties are assumed to vary according to exponential and power laws, respectively, in the tangential and the thickness directions. Parametric studies conducted for the variation of stresses and Displacements indicate that material properties can be tailored to satisfy several structural constraints. For the bending of a sandwich beam with a bi-directionally graded core and homogeneous isotropic facesheets, it is found that the maximum interfacial bending stress, the peak interfacial shear stress and the maximum interfacial peeling stress can be reduced, respectively, by 20%, 44% and 42%.
Andre La Gerche - One of the best experts on this subject based on the ideXlab platform.
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right precordial t wave inversion in healthy endurance athletes can be explained by lateral Displacement of the cardiac apex
JACC: Clinical Electrophysiology, 2015Co-Authors: M. Julia Brosnan, Guido Claessen, Andre La Gerche, David L. Prior, Hein HeidbuchelAbstract:Abstract Objectives The objective of this study was to test the hypothesis that T-wave inversion in the right precordial leads (TWI V2-3 ) reflects lateral Displacement of the heart such that the surface electrocardiographic (ECG) leads overlie a greater proportion of the right ventricle (RV). Background TWI V2-3 on ECG is more frequently observed among endurance athletes (EAs) than in the general population, the underlying mechanism for which is unclear. Methods Sixty-eight EAs and 41 nonathletic control subjects underwent ECG and cardiac magnetic resonance imaging (CMRI). In addition to standard measurements of biventricular function and volume, novel measurements of cardiac Displacement and orientation were analyzed from horizontal long-axis images. These included RV wall thickness in diastole (RV d ), cardiac-to-hemithorax area ratio (CHTx%), percentage of Circumferential Displacement of the RV apex toward the axilla (%LatD), and the angle of interventricular septum with respect to the thoracic midline (∠ septal ). Results All cardiac volume, RV d , CHTx%, %LatD, and ∠ septal values were greater in EAs than in controls. Compared to EAs without TWI V2-3 , EAs with TWI V2-3 (n = 26) did not have greater RV wall thickness or cardiac volumes (RV d = 4.9 vs. 4.8 mm, p = 0.695; LVEDV = 231 vs. 229 ml, p = 0.856; RVEDV = 257 vs. 254 mL, p = 0.746), but all measurements of cardiac Displacement toward the axilla were greater (%LatD = 45.6% vs. 37.9%, respectively, p septal = 54.23° vs. 48.63°, respectively, p = 0.001; and CHTx% = 46.3% vs. 41.9%, respectively, p = 0.048). Conclusions In healthy EAs, TWI V2-3 is associated with Displacement of the RV toward the left axilla rather than RV dilatation or hypertrophy. TWI V2-3 may be explained by the position of the RV relative to that of the surface ECG leads.
John N Oshinski - One of the best experts on this subject based on the ideXlab platform.
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demonstration of Circumferential heterogeneity in Displacement and strain in the abdominal aortic wall by spiral cine dense mri
Journal of Magnetic Resonance Imaging, 2019Co-Authors: Elizabeth Iffrig, John S Wilson, Xiadong Zhong, John N OshinskiAbstract:Background Knowledge of tissue properties of the abdominal aorta can improve understanding of vascular disease and guide interventional approaches. Existing MRI methods to quantify aortic wall Displacement and strain are unable to discern Circumferential heterogeneity. Purpose To assess regional variation in abdominal aortic wall Displacement and strain as a function of Circumferential position using spiral cine Displacement encoding with stimulated echoes (DENSE). Study type Prospective. Population Cardiovascular disease-free men (n = 8) and women (n = 9) ages 30-42. Sequences Prospective electrocardiogram (ECG)-gated and navigator echo-gated spiral, cine 2D DENSE and retrospective ECG-gated phase contrast MR (PCMR) sequences at 3T. Assessment In-plane Displacement values of the aortic wall acquired with DENSE were used to determine radial and Circumferential aortic wall motion. A quadrilateral-based 2D strain calculation method was implemented to determine strain from the Displacement field. Peak Displacement and its radial and Circumferential contributions as well as peak Circumferential strain were compared among eight Circumferential wall segments. Distensibility was calculated using PCMR and compared with homogenized Circumferential strain. Statistical tests To account for repeated measurements in volunteers, linear mixed models for mean sector values were created for Displacement magnitude, Circumferential Displacement, radial Displacement, and Circumferential strain. Comparisons were made between sectors. Calculated distensibility and homogenized Circumferential strain were compared using Bland-Altman analysis. Statistical significance was defined as P Results Displacement was highest in the anterior wall (1.5 ± 0.7 mm) and was primarily in the radial as compared with Circumferential direction (1.04 ± 0.05 mm vs. 0.81 ± 0.42 mm). Circumferential strain was highest in the lateral walls (left 0.16 ± 0.05 and right 0.21 ± 0.12) with homogenized Circumferential strain of 0.14 ± 0.05. Data conclusion DENSE imaging in the abdominal aortic wall demonstrated that the anterior aortic wall exhibits the greatest Displacement, while the lateral wall experiences the largest Circumferential strain. Level of evidence 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:731-743.
Anup Pydah - One of the best experts on this subject based on the ideXlab platform.
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shear deformation theory using logarithmic function for thick circular beams and analytical solution for bi directional functionally graded circular beams
Composite Structures, 2017Co-Authors: Anup Pydah, R C BatraAbstract:A shear deformation theory including a logarithmic function in the postulated expression for the Circumferential Displacement is developed for thick circular beams and is used to analytically solve static deformations of bi-directional functionally graded circular beams. The consideration of a logarithmic term is motivated by the Displacement field in the analytical solution of the plane strain elasticity problem of a hollow circular cylindrical shell. The non-zero shear traction boundary conditions at the two major surfaces of the beam are a priori satisfied by the assumed Displacement field. The material properties are assumed to vary according to exponential and power laws, respectively, in the tangential and the thickness directions. Parametric studies conducted for the variation of stresses and Displacements indicate that material properties can be tailored to satisfy several structural constraints. For the bending of a sandwich beam with a bi-directionally graded core and homogeneous isotropic facesheets, it is found that the maximum interfacial bending stress, the peak interfacial shear stress and the maximum interfacial peeling stress can be reduced, respectively, by 20%, 44% and 42%.
Jamshid Fariborz - One of the best experts on this subject based on the ideXlab platform.
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free vibration of bi directional functionally graded material circular beams using shear deformation theory employing logarithmic function of radius
Composite Structures, 2019Co-Authors: Jamshid Fariborz, R C BatraAbstract:Abstract Curved beams such as arches find ubiquitous applications in civil, mechanical and aerospace engineering , e.g., stiffened floors, fuselage , railway compartments, and wind turbine blades. The analysis of free vibrations of curved structures plays a critical role in their design to avoid transient loads with dominant frequencies close to their natural frequencies. One way to increase their applications and possibly make them lighter without sacrificing strength is to comprise them of Functionally Graded Materials (FGMs) that are composites with continuously varying material properties in one or more directions. Here, we study free vibrations of FGM circular beams by using a shear deformation theory that incorporates through-the-thickness logarithmic variation of the Circumferential Displacement , does not require a shear correction factor , and has a parabolic through-the-thickness distribution of the shear strain. The radial Displacement of a point is assumed to depend only upon its angular position. Thus the beam theory generalizes the Timoshenko beam theory. Equations governing transient deformations of the beam are derived by using Hamilton’s principle. Assuming a time harmonic variation of Displacements, and by utilizing a generalized differential quadrature method (GDQM), the free vibration problem is reduced to solving an algebraic eigenvalue problem whose solution provides frequencies and corresponding mode shapes. Results are presented for different spatial variations of the material properties, boundary conditions, and the beam aspect ratio. It is found that frequencies of the FGM beam are bounded by those of two geometrically identical homogeneous beams composed of the two constituents of the beam. Keeping other variables fixed, the change in the beam opening angle results in very close frequencies of the first two modes of vibration at a critical value of the opening angle, a phenomenon usually called mode transition. The critical opening angle is essentially the same for radially graded, bidirectionally graded and monolithic beams. It equals about 80° (60°) for clamped-clamped (hinged-hinged) beams.