Thick Cylinder Research Articles

Thermo-elasto-plastic analysis of thick-walled cylinder made of functionally graded materials using successive approximation method

In this paper, the thermo-elasto-plastic behavior of a thick walled cylindrical shell made of a Functionally Graded Material (FGM) is analyzed by Successive Approximation Method (SAM). The FGM ingredients include Aluminum and Silicon Carbide in which the effective material properties are estimated using the Modified Rule of Mixture. The shell is subjected to a combination of internal pressure and temperature gradient. After application of equilibrium equations for derivation of governing equations, the Differential Quadrature Method (DQM) is used for numerical solution. It is assumed that the two ends of the cylinder are closed and the plane strain conditions are established. The distribution of elastoplastic stresses and strains along the cylinder's thickness is presented in terms of characteristics of material composition and thermo-mechanical loadings such as volume fraction, in-homogeneous index, internal pressure and thermal loadings. Trueness and accuracy of the present problem is justified through comparison with available results in literature. The results show that by enhancement of ceramic particles percentage in the outer layers of cylinder's wall, amount of plastic strains is reduced at that layers, but at the same time, the amount of plastic strains and range of plastic region, increases at inner layers of thickness.

Contrast sensitivity and higher-order aberrations in Keratoconus subjects

This study analyzes the relationship between contrast-sensitivity and higher-order aberrations (HOA) in mild and subclinical-keratoconus in subjects with good visual-acuity (VA). Keratoconus group (including subclinical-keratoconus) and controls underwent autokeratometry, corneal-tomography, autorefraction and HOA measurement. Contrast-sensitivity was tested using a psychophysical two-alternative forced-choice Gabor patches in three blocks (6, 9, 12 cycles/deg). Controls were compared to the keratoconus group and to a keratoconus subgroup with VA of 0.00 LogMar group ("keratoconus-0.00VA"). Spearman correlation tested association between HOA and contrast-sensitivity. Twenty-two keratoconus subjects (38 eyes: 28 keratoconus, 10 subclinical-keratoconus, 20 keratoconus-0.00VA) and 35 controls were included. There was a significant difference between control and keratoconus, and between control and keratoconus-0.00VA, for keratometry, cylinder, thinnest and central corneal thickness (p < 0.001). Controls showed lower HOA and higher contrast-sensitivity for all spatial-frequencies (p < 0.001). Most HOA were negatively correlated with contrast-sensitivity for all spatial-frequencies for keratoconus group and for 9 and 12 cycles/deg for keratoconus-0.00VA. Keratoconus subjects with good VA showed reduction in contrast-sensitivity and increased HOAs compared to controls. HOA and contrast-sensitivity are inversely correlated in subjects with mild keratoconus despite good VA. This suggests that the main mechanism underlying the decreased vision quality in keratoconus is the increase of HOA.

Design of Circular Composite Cylinders for Optimal Natural Frequencies.

This study concerns optimizing the eigenfrequencies of circular cylindrical laminates. The stiffness properties are described by lamination parameters to avoid potential solution dependency on the initial assumptions of the laminate configurations. In the lamination parameter plane, novel response contours are obtained for the first and second natural frequencies as well as their difference. The influence of cylinder length, radius, thickness, and boundary conditions on the responses is investigated. The lamination parameters yielding the maximum response values are determined, and the first two mode shapes are shown for the optimum points. The results demonstrate that the maximum fundamental frequency points of the laminated cylinders mostly lie at the inner lamination parameter domain, unlike the singly curved composite panels. In addition, the second eigenfrequency shows a nonconvex response surface containing multiple local maxima for several cases. Moreover, the frequency difference contours appear as highly irregular, which is unconventional for free vibration responses.

Thermal Stresses Due to Non-Uniform Internal Heat Generation in Functionally Graded Hollow Cylinder

Thermal stresses of a functionally graded hollow thick cylinder due to non-uniform internal heat generation are studied in this paper. Analytical solutions are obtained with radially varying properties by using the theory of elasticity. Thermal stresses distribution for different values of the powers of the module of elasticity and varying power law index of heat generation are studied. The results have been computed numerically and illustrated graphically.

Dynamic response and optimization of functionally graded porous nanocomposite cylinders using a meshfree method

AbstractA new class of advanced ultralight composite materials has recently emerged through the use porous polymer matrix reinforced by carbon nanotubes. In this article, the dynamic response of functionally graded porous polymeric cylinders, reinforced by randomly oriented single‐walled carbon nanotubes, using a meshfree method is studied. Three different porosity distribution patterns are investigated: symmetric distribution (SYD), unsymmetric distribution, and uniform distribution. A thorough study on the effects of reinforcement volume fractions and porosity distribution patterns on the dynamic response of the structure has been carried out using the radial point interpolation meshfree method based on the 2D theory of elasticity. In addition, a Pareto front solution is obtained through a multiobjective optimization aimed at minimizing the weight and maximizing the natural frequency of the structure with porosity and reinforcement volume fraction as design variables. From a design perspective, the results indicate that the SYD porosity type is the best candidate for relatively thick cylinders because of its smaller mass and higher stiffness compared to the other distribution types. The current research presents a reliable computational framework to help provide an insight into the design of an optimum structure subject to dynamic loading.

The residually stressed unloaded state of arteries: Membrane and thin cylinder approximations

A solution is obtained for incompressible non-linearly elastic membranes that describes the bending of a cylindrical sector to form a perfect cylinder for a wide class of materials that includes isotropic materials and orthotropic materials reinforced by two families of mechanically equivalent fibres that are wound helically about the axial direction. Despite the relative simplicity of the physical problem, the solution of the corresponding boundary value problem for thick cylinders requires a numerical solution for even the simplest models. It is shown, however, that the thin shell solution provides an excellent approximation to the solution of the problem for cylindrical sectors whose thicknesses are an order of magnitude greater than that assumed for membranes. The approximate stress distribution in such thin shells is obtained. In these residually stressed cylinders, the radial stress is approximately zero but the hoop and axial stresses are finite. Estimates of the residual stresses in the unloaded state are obtained. A closed-form solution for the bending moment necessary to effect the deformation is also obtained.

Demagnetization Effect on the Magnetoelectric Response of Composite Multiferroic Cylinders

Strain-mediated multiferroic composite structures are gaining scientific and technological attention because of the promise of low power consumption and greater flexibility in material and geometry choices. In this study, the direct magnetoelectric coupling coefficient (DME) of composite multiferroic cylinders, consisting of two mechanically bonded concentric cylinders, was analytically modeled under the influence of a radially emanating magnetic field. The analysis framework emphasized the effect of demagnetization on the overall performance. The demagnetization effect was thoroughly considered as a function of the imposed mechanical boundary conditions, the geometrical dimensions of the composite cylinder, and the introduction of a thin elastic layer at the interface between the inner piezomagnetic and outer piezoelectric cylinders. The results indicate that the demagnetization effect adversely impacted the DME coefficient. In a trial to compensate for the reduction in peak DME coefficient due to demagnetization, a non-dimensional geometrical analysis was carried out to identify the geometrical attributes corresponding to the maximum DME. It was observed that the peak DME coefficient was nearly unaffected by varying the inner radius of the composite cylinder, while it approached its maximum value when the thickness of the piezoelectric cylinder was almost 60% of the total thickness of the composite cylinder. The latter conclusion was true for all of the considered boundary conditions.

Mechanical analysis of shrink-fitted thick FG cylinders based on first order shear deformation theory and FE simulation

In this paper, the first order shear deformation theory is used to derive an analytical formulation for shrink-fitted thick-walled functionally graded cylinders. It is assumed that the cylinders have constant Poisson’s ratio and the elastic modulus varies radially along the thickness with a power function. Furthermore, a finite element simulation is carried out using COMSOL Multiphysics, which has the advantage of defining material properties as analytical functions. The results from first order shear deformation theory are compared with the findings of both plane elasticity theory and FE simulation. The results of this study could be used to design and manufacture for elastic shrink-fitted FG cylinders.

Time fractional heat transfer analysis in thermally sensitive functionally graded thick hollow cylinder with internal heat source and its thermal stresses

The aim of this work is to investigate the time fractional thermoelastic state of a thermally sensitive functionally graded thick hollow cylinder subjected to internal heat source. Convection boundary conditions are applied on the curved surface of cylinder also sectional heating is assumed on the lower surface. The material properties except density and Poisson’s ratio are assumed to be dependent on temperature. Kirchhoff’s variable transformation is used to reduce the nonlinear heat conduction with temperature dependent thermal conductivity and specific heat capacity to linear form. Further the solution of linear form is obtained by using integral transform technique in the form of Bessel’s and trigonometric functions. All physical and mechanical quantities are taken as dimensional for the theoretical analysis whereas for numerical computations non-dimensional parameters are assumed. Numerical results of temperature change and stress distribution are illustrated graphically for ceramic-metal-based functionally graded materials and shown in figures with the help of Mathematica software.

AXISYMMETRIC PROBLEM OF THE ELASTICITY THEORY FOR THE RADIALLY INHOMOGENEOUS CYLINDER WITH A FIXED LATERAL SURFACE

By the method of the asymptotic integration of the equations of elasticity theory, the axisymmetric problem of elasticity theory is studied for a radially inhomogeneous cylinder of small thickness. It is considered that the elasticity moduli are arbitrary positive continuous functions of the radius of the cylinder. It is also assumed that the lateral surface of the cylinder is fixed, and stresses are imposed at the end faces of the cylinder, which leave the cylinder in equilibrium. The analysis is carried out when the cylinder thickness tends to zero. It is shown that solutions corresponding to the first and second iterative processes that determine the internal stress-strain state of the radially inhomogeneous cylinder with a fixed surface do not exist. The third iterative process defines solutions that have the boundary layer character equivalent to the Saint-Venant end effect on the theory of inhomogeneous plates. The stresses determined by the third iterative process are localized at the ends of the cylinder and decrease exponentially with distance from the ends. The asymptotic integration method is used to study the problem of torsion of the radially inhomogeneous cylinder of small thickness. The nature of the stress-strain state is analyzed.

Linear stability analysis of a boundary layer with rotating wall-normal cylindrical roughness elements

Abstract

Effects of structural and electromagnetic loads on vacuum vessel of Pakistan spherical Tokamak

This paper focuses on the effects of electromagnetic and structural loads on the vacuum vessel (VV) of Pakistan Spherical Tokamak (PST). The configured MAXWELL 3D and ANSYS Mechanical suits are used to investigate the different variables for structural analysis. The simulation is performed for transient current excitation of all coils and major plasma disruption, respectively. The electromagnetic (EM) loads derived from MAXWELL 3D are directly imported to the ANSYS Mechanical where structural loads are also assigned to VV. Stresses and deformations were determined from the associated loads. The 30° section of the VV with all coils is modeled in the design modeler and its step file format was imported to MAXWELL 3D. The section model was based on the axial symmetry of all coils system. By changing the thickness of inner cylinder of VV, the EM effects were studied. The variation of EM force, eddy current, and heat generation due to eddy current were studied with time for different thicknesses of the inner cylinder. As the thickness of inner cylinder decreases from 8 mm to 3 mm the magnitude of eddy current is observed to decrease uniformly for both cases (all coils and plasma disruption). The EM effect was found very strong in the case of coils transient. The results were compared using the design criterion of the RCC-Mx standard. It showed that PST geometry is safe, even 3 mm thickness of its inner cylinder can tolerate current transients of coils and associated dead loads based on the design criterion of the standard.

Analysis of SH wave in hollow piezo-composite cylinder with coupled imperfect interface condition

Present study primarily focuses on interpreting the propagation pattern of Shear horizontal (SH) wave in a piezo-composite layered cylinder. The structure consists of three concentric cylinders composed of hollow fiber-reinforced (FR) cylinder enclosed within piezomagnetic (PM) cylinder along the curved surface area which is similarly superimposed by a piezoelectric (PE) cylinder. The overall system is believed to be pre-stressed in a circumferential direction. The common boundary between each of the cylinder is demonstrated as imperfectly bonded. At the interface of PM and PE media, mechanical, electrical, magnetic and inter-coupled types of imperfections are assumed. Dispersion relations have been obtained for both the electrically open magnetically short (EOMS) and electrically short magnetically open (ESMO) circuit condition. Dispersion curves have been plotted to unravel the peculiarities of parameters like the radius of the hollow cylinder, thickness of FR and PM cylinder, thickness ratio of PM and PE cylinder, initial stress parameters, helical angle of the reinforcement. The influence of different interface parameters on the phase velocity of the wave has been studied and marked distinctly. For a detailed study, two successive modes have been plotted. Present study may help in improving the performance of piezo-composite cylindrical surface acoustic wave (SAW) sensors.

Analytical Solution of Aluminum Alloy Plates With Holes Subjected to Cold Expansion With Reverse Yielding

Abstract The expansion induced by cold working is a common process that generates residual stresses. It is used when fatigue damage accumulation and life reduction of aluminum alloy perforated plates is an issue in the aeronautics industry. This process is an attractive solution to extend the fatigue lifetime of these structures. It aims at generating residual stresses and increases thereby the strength of hollow parts including aluminum alloy plates with holes commonly used in the manufacture of airplane fuselage. Unfortunately, the life predictions require a good prediction of the residual stresses and in particular when reverse yielding takes place. An analytical model to predict the residual stresses induced during the expansion process due to the cold strain hardening is developed. The proposed analytical model is based on an elasto-plastic behavior, with a power law material behavior and relies on the theory of autofrettaged thick wall cylinders in plane strain state to which reverse yielding is incorporated. The application of Hencky theory of plastic deformation is used in the analytical calculations of the stresses and strains. Finite element numerical simulation is used to validate the developed analytical model by comparison of the radial, hoop, longitudinal, and equivalent stresses for both the loading and unloading phases. The obtained results show clearly that the level of residual stresses depend mainly on the interference and strain hardening while reverse yielding reduces the stresses near the hole.

Hybrid integral transform and p-version FEM for thermo-mechanical analysis of a functionally graded piezoelectric hollow cylinder subjected to asymmetric loads

As the first endeavor, a combination of fast Fourier transform and p-version of finite element method is proposed for electro-thermo-elastic analysis of a thick hollow cylinder under asymmetric thermal loadings. Especially in shells of revolution, the proposed FFT-pFE method is accompanied by a significant decrease in the computational costs. Due to the problem periodicity in such structures, the fast Fourier transform technique is used to discretize the governing equations into a set of harmonics in circumferential direction. Each harmonic is then partitioned using higher order finite elements. Hierarchical finite elements based on Legendre polynomial interpolation functions are utilized to discretize 2D governing equations of a functionally graded piezoelectric (FGP) cylinder. 3D governing equations of a FGP hollow cylinder are then discretized by using the higher-order Lagrangian finite elements. The effects of FFT grid-size as well as the order of the interpolation functions are investigated on convergence behavior of the proposed mixed FFT-pFE method. The piezoelectric material properties, with the exception of the Poisson’s ratio, are considered to vary along the radius of the cylinder and pursue the power function. The governing equations are derived using the principle of virtual displacements. For a 3D FGP hollow cylinder, the influence of ...

Multiaxial cyclic plasticity model including elastic modulus variation

In the present work a multiaxial model is proposed to describe the elastoplastic behaviour of a structural steel in the presence of loading-unloading cycles. The activity is a part of a more estensive research carried out in collaboration with Baker & Hughes aimed at developing an accurate model for accurately predicing residual stresses caused by autofrettage processes in thick cylinders and its experimental verification. It has been demostrated that in order to obtain estimates of the residual stress with errors within a few percent, the constitutive behavior of the material has to be reproduced very accurately. To this purpose, both the Bauschinger effect and the variation of the elastic modulus with the accumulated plastic deformation have to be accurately measured and properly included in the constitutive model.

Experimental and numerical analysis of roll bending process of thick metal sheets

In metalworking, bending forming processes are used extensively for a wide range of applications referring to several industrial fields, such as oil&gas field, naval field or automotive field. In cylinders and truncated cones bending process, three-point roll forming of metal sheets represents a concrete option, which mainly consists of pyramid-type machines made of two lower rolls and a top roll. Each roll can be designed to work as a driven roll or as an idler and to move both vertically and horizontally during the rolling process, depending on the sheet and final product features (mechanical properties, thickness and final curvature mainly). Final products can be affected by defects, which represent a concrete problem for metalworking industries because of the further works to be done to meet customers needs; in three-point roll bending, warping defect and hourglass (or barrel) defect represent two of the most common problems. In this paper, an experimental and numerical analysis is proposed to detect defects on roll-bent thick cylinders referring to several companies experiences; the occurrence of thickness variability and circumferences variability along cylinder length and considerable differences between the internal and external length of cylinders themselves, referable to the so-called ”hourglass defect” represents a common problem in this industrial field and a major cost for metalworking companies. A Finite Element (FE) 3D model of both the roll-bending machine and the metal sheet is used to simulate the mechanical behaviour of the metal sheet during the forming process, checking for the influence of the spring-back effect and the bending moments from the rolls. Both the pre-bending and the roll bending phases have been simulated. Rolls are modelled as rigid. Both rolls and sheet have been modelled using solid elements and contact elements to take into account rolls/sheet friction. Obtained results are compared with experimental results to check the reliability of the FE model and the simulation. The model itself is then implemented with a central lower roll which serves as an idler and is placed half-way between the original ones. The updated model is then used to simulate the process again and test the central idler as an hourglass-defect solution.

Active broadband sound transmission loss control through an arbitrary thick smart Piezo-laminated cylinder

The feedback control strategy is utilized for the enhancement of the sound transmission loss (STL) through an infinite thick hollow Piezo-laminated cylinder of arbitrary thickness insonified by an oblique progressive incident plane wave. The close form formulation is accomplished by utilizing the sound wave equation, the three-dimensional (3D) exact theory of elasticity and piezoelasticity. The active control strategy is achieved by sending a control signal from the distributed piezoelectric sensor layer through a controller with certain feedback gain to drive the external piezoelectric actuators. The mechanical stress generated by the piezo-actuator layer cancels the parts of the input incident wave to enhance the STL. Comprehensive numerical studies are carried out to investigate the poling direction and feedback gain effects on the STL. The results show that in the case of radially polarized piezoelectric materials, the feedback control provides significant sound enhancement especially, when the angle of the incident wave is close to normal, however, in the case of axially polarized piezoelectric materials, the control feedback strategy reduces the unfavorable oscillatory motion of the cylinder in addition to providing a superior sound isolation enhancement, particularly for near-grazing incident angles. The accuracy of the proposed solution is confirmed by comparing the presented results with the ones from the simplified models in the literature as well as the commercial finite element package Comsol Multiphysics.

Stress waves in thick porous graphene-reinforced cylinders under thermal gradient environments

In this paper, the propagation of stress waves in thick porous graphene-reinforced cylinders (TPGRCs) is investigated using a meshless solution based on an axisymmetric model and moving least squares (MLSs) interpolation functions. The cylinders are assumed under a steady state thermal gradient effect along with an initial deflection response obtained from the static solution of the same cylinder subjected to a static internal pressure. To improve the design of such TPGRCs, functionally graded (FG) profiles are considered for the distribution of graphene nanofillers along their radial direction. Moreover, pores are non-uniformly embedded inside the cylinders to decrease the weight of TPGRCs. The material properties of porous and nanocomposite materials are calculated as functions of temperature using a closed cell model and a modified Halpin-Tsai (HS) technique, respectively. Considering structural damping for the system, the influences of embedding porosity, the temperature of each surface, reinforcing with graphene and the thickness of cylinder on the stress wave responses of TPGRCs have been investigated. The results reveal that the increase of porosity volume inside TPGRCs significantly increases the amplitudes and stationary time of deflections; however, it reduces the values of stationary deflections and stresses, along with the reduction of propagation speeds.

Transient thermal stress analysis for a short thick hollow FGM cylinder with nonlinear temperature-dependent material properties

In this study, nonlinear transient thermo-elastic analysis for a thick hollow 1D-FGM (functionally graded material) axisymmetric cylinder with finite length is investigated using higher-order graded finite element method. The material property gradations are along the radial direction and the power-law volume fraction and simple rule of mixture scheme are utilized to perform the effective material properties. As the cylinder exposed to high temperature, the temperature dependency of material properties is considered. So it led to nonlinear thermal conduction equation and in spite of the material distribution along one-direction by changing the temperature, the material properties are varied along two-direction with time. The nonlinear heat equation leads to 2D-temperature distribution for an axisymmetric cylinder. Also the thermal stress field would be different from an infinite cylinder which has been studied before. The temperatures, displacements and stresses for different values of volume fraction exponents along radial direction are investigated. It is revealed that the stresses and temperature in FGM cylinder are lower than the ceramic rich one. In other words, functionally graded cylinder wall gives better results in both stress and temperature cases than non-FGM cylinder.