Thick Cylinder Research Articles

Distribution of Mode I Stress Intensity Factors for Single Circumferential Semi-Elliptical Crackin Thick Cylinder

In this paper, mode I stress intensity factors (SIFs) are calculated numerically by finite element software ANSYS, for a single semi-elliptical circumferential crack on a thick cylinder. The examined cracks were located either on the external or internal surface of the cylinder and subjected to two different types of loadings, tension and internal pressure, applied separately. To present results in a more comprehensive form, dimensionless analysis is used, and a wide variation limit of parameters that define the crack geometry is considered. The ratio of crack depth to crack length ranging between 0.4 to 1.2, the ratio of crack depth to cylinder wall thickness vary between 0.2, 0.5 and 0.8, and the ratio of the cylinder wall thickness to the cylinder internal radius 0.25. Based on the obtained results, distributions of SIFs found to be symmetric along the crack front. The location where the maximum SIFs on the crack front attained is strongly affected by the change of aspect ratio, and external cracks generally exhibit a higher SIFs than those of internal cracks. It is also found a significant effect for the relative depth of the crack on SIFs value, which could accelerate the fracture process.

An optimal design model for the wall thickness of the propellant tank

The propellant tank is a vital part for the liquid rocket, and the optimal design of the propellant tank is a significant research to develop the heavy rocket. This paper aims at providing an optimal design model for tank wall thickness. Through establishing the tank mathematical model, analyzing the stress distributions of tank, and defining the equivalent stress of tank, the wall thickness parameters of tank roof, cylinder, and bottom are obtained. The effects of tank parameters on the wall thickness are analyzed to determine the distribution rules of tank roof, cylinder, and bottom wall thickness parameters. Combined with the safety factor that is defined as the ratio of the material's ultimate stress to the maximum equivalent stress, the optimal design model with invariable tank roof and bottom wall thicknesses and variable tank cylinder wall thickness is established. Finally, the optimal design model is verified by comparing the optimal tank with the original tank. The results show that the optimal design model can effectively decrease the mass of the tank and improve the stress distribution of the tank.

Static Modeling of Miniaturized Pneumatic Artificial Muscles, Kinematic Analysis, and Experiments on an Endoscopic End-Effector

In this paper, we present the design, development, modeling, and experimental validation of an endoscopic attachment that can be used to independently position an endoscopic catheter tip at a desired location. Three miniaturized pneumatic artificial muscles (MPAMs) are used in a flexible endoscopic attachment, each MPAM is of 1.2 mm diameter and 45 mm in length and placed approximately 120 degrees apart within a pair of concentric springs. Pressurizing one or more MPAMs allows the tip to be positioned in a workspace, which is approximately a hemispherical section of radius 45 mm. We present a new and improved theoretical model for pressure-deformation relationship of a MPAM using static equations of a pressurized thick cylinder and constraints due to the braids. Comparison with existing models show that the proposed model performs better and the errors predicted by the model are less than 5% with experiments. A new forward kinematic model relating the position and orientation of the tip of the end-effector with changes in MPAM lengths is developed. Finally, we present experimental results conducted on a prototype endoscopic attachment and show that our model could predict the pose of the end-effector with a maximum error of 2 $\pm$ 1 mm.

Fungi–plant–arthropods interactions in a new conifer wood from the uppermost Permian of China reveal complex ecological relationships and trophic networks

An exceptionally well-preserved wood, Ningxiaites shitanjingensis sp. nov., is described from the uppermost Permian Sunjiagou Formation of Northwest China providing new evidence for plant diversity and paleoecological features of the Cathaysian Flora. The new plant is characterized by a eustelic vascular system with thick pycnoxylic woody cylinder. The cylindrical pith is solid and parenchymatous, surrounded by numerous, discrete endarch primary xylem strands and monarch leaf traces. The wood is especially distinctive by the expanded rays at the pith periphery and the pitted tangential walls of ray cells. The tracheids in the primary xylem have annular, helical and scalariform thickenings from protoxylem to metaxylem. The secondary xylem comprises tracheids, rays and axial parenchyma cells. Tracheids in the secondary xylem possess both alternate and opposite bordered pits on the radial walls. Each cross-field displays 1–2 cupressoid bordered pits. Rays are mostly uniseriate, 1–14 cells high. Leaf traces originate individually, bifurcate or not during their horizontal extension through wood, form helical clusters. Two types of arthropod coprolites were recognized in a boring in the pith. The relatively smaller coprolites containing unidentifiable plant tissues are identical with those of oribatid mites, whereas the larger coprolites exhibiting undigested plant cells probably produced by ancient millipedes. In addition to the occurrences of evident fungal hyphae, white-rot pattern and tyloses in the delignificated wood. The current study demonstrates complex ecological relationships and trophic networks occurred during the Lopingian (late Permian).

Extreme events and non-Kolmogorov spectra in turbulent flows behind two side-by-side square cylinders

Turbulent flows behind two side-by-side square cylinders with three different gap ratios, namely, $L_{d}/T_{0}=4,$ 6 and 8 ($L_{d}$ is the separation distance between two cylinders and $T_{0}$ is the cylinder thickness) are investigated by using direct numerical simulations. Depending on the strength of the gap flow, the three cases can generally be characterized into two regimes, one being the weak gap flow regime and the other being the robust gap flow regime. The wake-interaction length scale can only be applied to characterize the spatial evolution of the dual-wake flow in the robust gap flow regime. And only in this regime can the so-called ‘extreme events’ (i.e. non-Gaussian velocity fluctuations with large flatness) be identified. For the case with $L_{d}/T_{0}=6$, two downstream locations, i.e. $X/T_{0}=6$ and 26, at which the turbulent flows are highly non-Gaussian distributed and approximately Gaussian distributed, respectively, are analysed in detail. A well-defined $-5/3$ energy spectrum can be found in the near-field region (i.e. $X/T_{0}=6$), where the turbulent flow is still developing and highly intermittent and Kolmogorov’s universal equilibrium hypothesis does not hold. We confirm that the approximate $-5/3$ power law in the high-frequency range is closely related to the occurrences of the extreme events. As the downstream distance increases, the velocity fluctuations gradually adopt a Gaussian distribution, corresponding to a decrease in the strength of the extreme events. Consequently, the range of the $-5/3$ power law narrows. In the upstream region (i.e. $X/T_{0}=6$), the second-order structure function exhibits a power-law exponent close to $1$, whereas in the far downstream region (i.e. $X/T_{0}=26$) the expected $2/3$ power-law exponent appears. The larger exponent at $X/T_{0}=6$ is related to the fact that fluid motions in the intermediate range can directly ‘feel’ the large-scale vortex shedding.

Analytical expressions for determining deflections, stresses and the required thickness of the orthotropic pressure cylinders

On the basis of the moment theory of orthotropic shells of revolution and the theory of the boundary effect, analytical expressions have been obtained for deflections, stresses and the necessary thickness of orthotropic cylindrical pressure cylinders with bottoms. This analytical expressions are convenient for practical use.

Nonlinear Buckling Finite Element Analysis to Estimate Collapse Pressure of Thick Cylinder under Hydrostatic Pressure

In order to perform a pressure chamber experiment with a circular cylindrical pressure vessel, the dimensions of the cylinder need to be determined in the range of the maximum externally applied pressure of the chamber to create the collapse process. In this study, the collapse load values from published chamber test results, finite element analysis and the theory of thick cylinders were thoroughly compared in a aluminum cylinder. In order to investigate the effect of collapse load according to the ovality during manufacturing, nonlinear buckling analysis was performed and the collapse load according to ovality was compared. Based on the results, the dimensions of the steel cylinder were determined for the future chamber collapse test.

Buckling of Radially Loaded Concrete Cylinders in Fire Condition

Concrete cylinders are commonly used in water treatment and sewerage plants, in the form of wells or basins. They are mainly subjected to axial compression resulting from soil lateral pressure and aqueous hydrostatic pressure, in case of the presence of a groundwater table; that is why they are mostly designed in the form of a circular hollow section. Concrete cylinders face a complicated case of loading in fire condition, as a result of material degradation in addition to thermally induced stresses. This paper studies buckling stability of that case where, a concrete cylinder is subjected to an internal fire load in addition to superimposed structural loads from the surrounding environment. The main objective of the research is to study buckling stability of concrete cylinders through identifying various structural and thermal parameters, controlling that behaviour. Finite element modelling using "Ansys 18.1" has been chosen as an approach to deal with the research problem. Twenty-five solid elements models have been prepared to study both thermal and structural behaviour of concrete cylinders in fire condition. Cylinder thickness, slenderness ratio, load ratio, and groundwater presence have been adopted as main research parameters to identify their effect on well's fire buckling endurance, in accordance with ISO 834 standard fire curve. A parametric study has been designed to study fire endurance vulnerability to cylinder thickness ranging from 50 mm up to 800 mm; diameter to thickness ratio [D/t] ranging from "10" up to "160"; full spectrum of structural load ratios; in addition to the presence of a surrounding groundwater. Outputs of the parametric study have been introduced in the form of figures, which could be used as preliminary design aids to identify buckling fire endurance as function of load ratio for various spectrums of thickness and slenderness ratios. Moreover, critical thicknesses and load ratios have been revealed.

On modeling of carbon nanotubes reinforced materials and on influence of carbon nanotubes spatial distribution on mechanical behavior of structural elements

A recently developed approximate approach for modeling of carbon nanotubes and for evaluation of the effective properties of carbon nanotubes reinforced materials is applied to analysis of square plate with hole under uniaxial tension. It is assumed, that the plate is made of polymer with randomly distributed and randomly oriented carbon nanotubes. Distributions of carbon nanotubes volume fraction is varied over the surface of the plate, with the constraint that the total volume of nanotubes in the structure is the same, and the effects of that on stress concentration is evaluated. Such special variation volume fraction makes the carbon nanotubes reinforced polymer a functionally graded material.In evaluation of the local effective properties the Gutrin–Murdoch material surface model is applied to a hollow cylinder of finite thickness and combined with the notion of energy equivalence to replace carbon nanotube with an equivalent solid cylinder. The interphase, if any, can be modeled as a spring layer and subsequently added to obtain another equivalent solid cylinder. The material reinforced with such solid cylinders is then evaluated using the method of conditional moments, a stochastic homogenization approach proposed earlier for determination of the effective properties of random materials.

ЗАДАЧА КРУЧЕНИЕ ДЛЯ РАДИАЛЬНО-НЕОДНОРОДНОЙ ТРАНСВЕРСАЛЬНО-ИЗОТРОПНОГО ЦИЛИНДРА МАЛОЙ ТОЛЩИНЫ (Torsion Problem for Radially Nonhomogeneous Transversally Isotropic Cylinder of Small Thickness)

Russian Abstract: Методом асимптотического интегрирования уравнений теории упругости исследована задача кручения радиально-неоднородного трансверсально-изотропного цилиндра малой толщины. В предположении достаточной гладкости нагрузки с помощью асимптотического метода строятся неоднородные решения. Дан алгоритм построения точных частных решений уравнений равновесия для специальных видов нагрузок, боковая поверхность цилиндра которых нагружена силами, полиномиально зависящими от осевой координаты. Построены однородные решения. Основываясь на асимптотическом методе, проведен качественный анализ напряженно-деформированного состояния цилиндра. English Abstract:The torsion problem of radially isotrophic cylinder of small thickness is investigated by the asymptotic integration method of equations of elasticity theory [1]. In assumption of sufficient smoothness of loading by means of asymptotic method the nonhomogeneous solution is constructed. Algorithm of exact solutions of equilibrium equations is given for special form of loading, whose lateral surface of cylinder is loaded by force, depending on polynomial from axis coordinate. The homogeneous solutions are constructed. Based on asymptotic method, the qualitative analyses of deflected mode of cylinder is carried out.

Morphoelastic fiber remodeling in pressurized thick-walled cylinders with application to soft tissue collagenous tubes

We consider the mechanics of fiber remodeling in a pressurized thick walled cylinder where our focus is on the interaction between inflation and remodeling. The material is taken to consist of an incompressible neo-Hookean ground substance matrix in which the fibers are embedded. The fiber network is assumed to undergo a stretch mediated remodeling process, as suggested by experiments on enzymatic degradation of collagen fibers in biological soft tissues. In our treatment, such a remodeling process is defined in terms of a constant fiber-creation rate, and a fiber-dissolution rate that decreases with the amount of fiber stretch. Here we study how pressure loading of a tube affects this process within the cylindrical wall. The impact of two basic load carrying fibers models on the remodeling of the fiber network are explored, as well as the effect of two different choices for the fiber's natural configuration when replacement fibers are first synthesized.

Transformer position sensor for a pneumatic cylinder

A novel transformer-based sensor for a pneumatic cylinder enables measurements of the piston position to be made through a thick conductive cylinder. Unlike existing industrial solutions, which are mainly based on a moving magnet, our sensors do not require modifications to the parts inside the cylinder.Finite element analysis results are compared with measurements at various piston positions and excitation frequencies. Using a suitable model for the magnetic properties of the iron piston bar, we achieved good agreement between the model and reality.When the sensor is operated at 100 Hz, the sensitivity is 200 mV/FS and the raw linearity error is 1.6% of the full 400 mm stroke.

INTERNAL FORCE ANALYSIS AND EXPERIMENTAL INVESTIGATIONS OF WIDE-GAP CONCRETE BEAMS STRENGTHENED WITH NEARSURFACE MOUNTED CARBON FIBER REINFORCED PLASTIC BARS

The internal force analysis was made on three media of the carbon fiber reinforced plastic (CFRP) bar, adhesive and concrete and two interfaces including the CFRP to adhesive and concrete to adhesive interfaces of wide-gap beams strengthened with near-surface mounted carbon fiber reinforced plastic bars. The findings show that the shear stress is the main part of the stress in the CFRP bar-adhesive-concrete interfaces. It is more convenient to obtain the interface strength by destruction tests of wide-gap concrete beams strengthened with near-surface mounted (NSM) CFRP bars. A CFRP bar under forces is equivalent to a cylinder that bears shear stress and normal stress on the surface. The shear stress was provided by the bonding force, and the effects of normal stress can be ignored. The average shear stress on the surface of a CFRP bar can be obtained by strain gages in the wide gap. The analysis results are in good agreement with the experimental results. The distribution of cross-sectional normal stress of the carbon fiber reinforced plastic bar is non-uniform and exhibits a power distribution along the length, which leads to certain differences about the deformation between the center and the edge of the cross section of the CFRP bar. The adhesive cohesive body after solidification inside the groove is a column section circle that can be approximately assumed as a thick wall cylinder. The glue cohesion in the tangential and radial stress has almost no effect on the shear deformation of the adhesive cohesive body. Interfacial debonding damage occurred in the concrete near the interface. The concrete strength will significantly affect the performance and the peel bond strength.

Cross bore size and wall thickness effects on elastic pressurised thick cylinders

Three-dimensional finite element analyses were performed on closed-ended thick-walled cylinders with a radial cross bore under internal pressure. The aim of this study was to determine the behaviour of the hoop stress as well as to establish the optimal Stress Concentration Factors (SCF). Cylinders of thickness ratios of 3.0 down to 1.4 with cross bore size ratios (cross bore to main bore ratio) ranging from 0.1 to 1.0 were studied. The maximum hoop stress was found to increase with the increase in the cross bore size. Amongst the five different circular radial cross bore size ratios studied, the smallest cross bore size ratio of 0.1, gave the lowest hoop stress while the highest stress occurred with a cross bore size of 1.0. Moreover, the lowest SCF occurred in the smallest cross bore size ratio of 0.1 at a thickness ratio of 2.25 with a SCF magnitude of 2.836. This SCF magnitude indicated a reduction of pressure-carrying capacity of 64.7% in comparison to a similar plain cylinder without a cross bore.

Thermal shock experiment of beryllium exposed to intense high energy proton beam pulses

Beryllium is a material extensively used in various particle accelerator beam lines and target facilities, as beam windows and, to a lesser extent, as secondary particle production targets. With increasing beam intensities of future multimegawatt accelerator facilities, these components will have to withstand even greater thermal and mechanical loads during operation. As a result, it is critical to understand the beam-induced thermal shock limit of beryllium to help reliably operate these components without having to compromise particle production efficiency by limiting beam parameters. As part of the RaDIATE (radiation damage in accelerator target environments) Collaboration, an exploratory experiment to probe and investigate the thermomechanical response of several candidate beryllium grades was carried out at CERN's HiRadMat facility, a user facility capable of delivering very-high-intensity proton beams to test accelerator components. Multiple arrays of thin beryllium disks of varying thicknesses and grades, as well as thicker cylinders, were exposed to increasing beam intensities to help identify any thermal shock failure threshold. Real-time experimental measurements and postirradiation examination studies provided data to compare the response of the various beryllium grades, as well as benchmark a recently developed beryllium Johnson-Cook strength model.

Theoretical and experimental investigation on interference fit in electromagnetic riveting

As an advanced interference-fit joining technology, electromagnetic riveting (EMR) has wide engineering application prospects in manufacturing and assembly fields. In this paper, a theoretical model on interference fit for EMR process is derived based on the stress wave theory and thick wall cylinder theory. EMR experiments are conducted to verify the analytical model. The compared results show that the analytical solutions agree well with experimental values. The interference-fit model synthetically considers many process parameters factors, not only the material properties and size of rivet, sheets and punch, but also the riveting force. The residual stress distribution, which is an important factor on fatigue life, can be predicted by this model. In addition, this can provide scientific guidance for the process parameter design and riveting setup optimization in engineering application.

Analysis of axisymmetric problem from the theory of elasticity for an isotropic cylinder of small thickness with alternating elasticity modules

Asymptotic methods play an important role in solving three-dimensional elasticity problems. The method of asymptotic integration of three-dimensional equations of elasticity theory takes an important place in solving the problems of the limited transition from three-dimensional problems to two-dimensional for elastic membranes. Based on the method of asymptotic integration of equations of the elasticity theory, the axisymmetric problem of elasticity theory for radially non-homogeneous cylinder of small thickness is explored. The case when elasticity modules change by the radius according to the linear law is considered. It is expected that the lateral part of the cylinder is free from stresses and boundary conditions, leaving a cylinder in equilibrium, are assigned at the ends of a cylinder. The stated boundary-value problem is reduced to the spectral problem. The behavior of solutions to the spectral problem both in the inner part of a cylinder, and near the ends of a cylinder if the parameter of thinness of cylinder’s walls tends to zero, is studied. Three groups of solutions were obtained and the nature of the constructed homogeneous solutions was explained. The solution corresponding to the first iterative process determines the penetrating stressed-strained state of a cylinder. The solution corresponding to the second iterative process represents edge effects in the applied theory of shells. The third iterative process determines the solution which has the character of a boundary layer. The solution corresponding to the first and second iterative processes determines the internal stressed-strained state of the cylinder. In the first term of asymptotics, they can be regarded as a solution on the applied theory of shells. It was shown that the stressed-strained state, similar to the case of a homogeneous cylinder of small thickness, consists of three types: penetrating stressed state, simple edge effect and a boundary layer. The problem of meeting the boundary conditions on the ends of a radially non-homogeneous cylinder using the Lagrangian variation principle was considered.

Best Level of Parameters for a Critical Buckling Load for Circular Thin- Walled Structure Subjected to Bending

Circular thin walled structures have wide range of applications. This type of structure is generally exposed to different types of loads, but one of the most important types is a buckling. In this work, the phenomena of buckling was studied by using finite element analysis. The circular thin walled structure in this study is constructed from; cylindrical thin shell strengthen by longitudinal stringers, subjected to pure bending in one plane. In addition, Taguchi method was used to identify the optimum combination set of parameters for enhancement of the critical buckling load value, as well as to investigate the most effective parameter. The parameters that have been analyzed were; cylinder shell thickness, shape of stiffeners section and the number of stiffeners. Furthermore, to verify the contribution of parameters on buckling response, the analysis of variance technique (ANOVA) method was implemented, which gave the contribution weight as percentages. The analysis of results by these two methods showed that the more effective parameter on the critical buckling load was the thickness of cylinder’s shell and the lowest effective was the number of stiffeners The values of parameters that gave the best critical buckling load combination were: 1) the ratio of cylinder’s diameter to thickness of its shell was 133, 2) the ratio of the depth to thickness of stiffeners was1.6, and 3) the number of stiffeners was 12.

3D numerical study of natural convection heat transfer from a hollow horizontal cylinder placed on the ground

In the present work, natural convection heat transfer from a thick hollow horizontal cylinder placed on ground is studied numerically. 3D numerical simulations have been performed by varying the Rayleigh number (Ra) from 104 to 108 (preferably within laminar regime). All the simulations have been carried out by varying length to outer diameter ratio (L/D) and thickness ratio (d/D) in the range of 0.2–20 and 0.4–0.9 respectively. Nusselt number, heat transfer rate and contribution to total heat transfer rate from different surfaces have been calculated and their variation with the above parameter is represented graphically. Similarly, thermal plume and velocity vector are shown pictorially at different sections of the cylinder and physical phenomenon of fluid flow and heat transfer could be described from such pictures. Later on effect of above parameters on cooling time is also discussed. It has been observed that with increase in thickness, Nu decreases at low L/D (L/D ≤ 2), whereas at higher L/D a reverse trend is observed. Heat transfer rate from the inner surface increases initially with increase in L/D and after a particular L/D, it attains constant value whereas for outer surface, it increases continuously. It has been also observed that at a particular L/D and d/D, contribution of heat transfer rate from inner surface increases with Ra, whereas reverse trend is observed for outer and side flat surface. A correlation for Nusselt number as a function of Rayleigh number, L/D and d/D has been developed which may be useful for industrial purposes.

Evaluation of the Rotor Eddy-Current Losses in High-Speed PMSMs With a Shielding Cylinder for Different Stator Sources

A continuous demand for more efficient and more compact drives is pushing the popularity of high-speed permanent magnet synchronous machines (PMSMs). However, high rotational speeds and extreme power densities imply that an appropriate cooling of the rotor may be difficult. This is all the more important because of the risk of demagnetization when permanent magnets are operated at high temperatures. Therefore, it is paramount to reduce the losses in the rotor of high-speed machines as much as possible. One technique to reduce the eddy-current losses is introducing a shielding cylinder, i.e., a conductive sleeve that is wrapped around the magnets. However, when badly designed, such a shielding cylinder may increase, rather than decrease, the losses. Therefore, an in-depth study of the effect of the shielding cylinder on the eddy-current losses in high-speed PMSMs is required. By studying how the eddy-current losses are affected by the shielding cylinder's thickness and its conductivity, this paper aims at providing more insight in how the eddy-current losses can be reduced. Moreover, the study of the eddy-current losses is repeated for different stator sources to evaluate the importance of accounting for the actual control strategy during the machine's design.