Showing papers on "Internal pressure published in 2013"

Compressible air entrapment in high-speed drop impacts on solid surfaces

Abstract: Using high-speed photography coupled with optical interference, we experimentally study the air entrapment during a liquid drop impacting a solid substrate. We observe the formation of a compressed air film before the liquid touches the substrate, with internal pressure considerably higher than the atmospheric value. The degree of compression highly depends on the impact velocity, as explained by balancing the liquid deceleration with the large pressure of the compressed air. After contact, the air film expands vertically at the edge, reducing its pressure within a few tens of microseconds and producing a thick rim on the perimeter. This thick-rimmed air film subsequently contracts into an air bubble, governed by the complex interaction between surface tension, inertia and viscous drag. Such a process is universally observed for impacts above a few centimetres high.

Finite inflation analysis of a hyperelastic toroidal membrane of initially circular cross-section

Abstract: In this work, we have studied the finite inflation of a hyperelastic toroidal membrane with an initially circular cross-section under internal pressure. The membrane material is assumed to be a Mooney–Rivlin solid. The inflation problem is formulated as a variational problem for the total potential energy comprising the membrane strain energy and internal energy of the gas. The problem is then discretized and solved up to a high degree of accuracy through a sequence of approximations based on the Ritz expansion of the field variables combined with a potential energy density perturbation and Newton–Raphson method. The effects of the inflation pressure and material properties on the state of stretch and geometry of the inflated torus have been studied, and some interesting results have been obtained. The stability of the inflated configurations in terms of impending wrinkling of the membrane has been investigated on the principal stretch parameter plane for both isotropic and anisotropic (transversely isotropic) material cases. Certain shape factors quantifying the geometry of the membrane have been defined and calculated which characterize the cross-sectional shape and size of the torus during inflation.

Evidence for length-dependent wire expansion, filament dedensification and consequent degradation of critical current density in Ag-alloy sheathed Bi-2212 wires

Abstract: It is well known that longer Bi-2212 conductors have significantly lower critical current density (Jc) than shorter ones, and recently it has become clear that a major cause of this reduction is internal gas pressure generated during heat treatment, which expands the wire diameter and dedensifies the Bi-2212 filaments. Here we report on the length-dependent expansion of 5–240 cm lengths of state-of-the-art, commercial Ag alloy sheathed Bi-2212 wire after full and some partial heat treatments. Detailed image analysis along the wire length shows that the wire diameter increases with distance from the ends, longer samples often showing evident damage and leaks provoked by the internal gas pressure. Comparison of heat treatments carried out just below the melting point and with the usual melt process makes it clear that melting is crucial to developing high internal pressure. The decay of Jc away from the ends is directly correlated to the local wire diameter increase, which decreases the local Bi-2212 filament mass density and lowers Jc, often by well over 50%. It is clear that control of the internal gas pressure is crucial to attaining the full Jc of these very promising round wires and that the very variable properties of Bi-2212 wires are due to the fact that this internal gas pressure has so far not been well controlled.

Finite element analysis of filament-wound composite pressure vessel under internal pressure

Abstract: In this study, finite element analysis (FEA) of composite overwrapped pressure vessel (COPV), using commercial software ABAQUS 6.12 was performed. The study deals with the simulation of aluminum pressure vessel overwrapping by Carbon/Epoxy fiber reinforced polymer (CFRP). Finite element method (FEM) was utilized to investigate the effects of winding angle on filament-wound pressure vessel. Burst pressure, maximum shell displacement and the optimum winding angle of the composite vessel under pure internal pressure were determined. The Laminae were oriented asymmetrically for [00,00]s, [150,-150]s, [300,-300]s, [450,-450]s, [550,-550]s, [600,-600]s, [750,-750]s, [900,-900]s orientations. An exact elastic solution along with the Tsai-Wu, Tsai-Hill and maximum stress failure criteria were employed for analyzing data. Investigations exposed that the optimum winding angle happens at 550 winding angle. Results were compared with the experimental ones and there was a good agreement between them.

Effect of internal fluid pressure on quality of aluminum alloy tube in rotary draw bending

Abstract: In the present study, the rotary draw bending of aluminum alloy tubes with internal fluid pressure is investigated by finite element simulation and experiments. The effect of the internal pressure on the cross-section ovality, wall thinning, and wall thickening was studied. The results show that the internal pressure has a significant effect on cross-section quality of aluminum alloy bent tubes. As the internal pressure increases, the cross-section ovality and the wall thickening decrease, and the wall thinning increases. The effect of internal pressure on wall thinning is more significant than its effect on wall thickening.

Volume shrinkage of a metal–organic framework host induced by the dispersive attraction of guest gas molecules

Abstract: Using a density functional theory calculation including van der Waals (vdW) corrections, we report that H2 adsorption in a cubic-crystalline microporous metal–organic framework (MOF-5) leads to volume shrinkage, which is in contrast to the intuition that gas adsorption in a confined system (e.g., pores in a material) increases the internal pressure and then leads to volumetric expansion. This extraordinary phenomenon is closely related to the vdW interactions between MOF and H2 along with the H2–H2 interaction, rather than the Madelung-type electrostatic interaction. At low temperatures, H2 molecules adsorbed in the MOF-5 form highly symmetrical interlinked nanocages that change from a cube-like shape to a sphere-like shape with H2 loading, helping to exert centrosymmetric forces and hydrostatic (volumetric) stresses from the collection of dispersive interactions. The generated internal negative stress is sufficient to overcome the stiffness of the MOF-5 which is a soft material with a low bulk modulus (15.54 GPa).

A new closed-form solution for analysis of unlined pressure tunnels under seepage forces

Abstract: SUMMARY In this study, a simplified analytical closed-form solution, considering plane strain and axial symmetry conditions, for analysis of a circular pressure tunnel excavated underwater table, is developed. The method accounts for the seepage forces with the steady-state flow and is based on the generalized effective stress law. To examine the effect of pore pressure variations and also the boundary conditions at the ground surface, the formulations are derived for different directions around the tunnel. The proposed method can be applied for analysis and design of pressure tunnels. Illustrative examples are given to demonstrate the performance of the proposed solution and also to examine the effect of seepage forces on the stability of tunnels. The simplified analytical solution derived in this study is compared with numerical analyses. It is concluded that the classic solutions (Lame's thick-walled solution), considering the internal pressure as a mechanical load applied to the tunnel surface, are not applicable to pervious media and can result in an unsafe design. Copyright © 2012 John Wiley & Sons, Ltd.

Continuum Damage Mechanics Analysis of Thin-Walled Tube Under Cyclic Bending and Internal Constant Pressure

Abstract: Ratcheting and fatigue damage of thin-walled tube under cyclic bending and steady internal pressure is studied. Chaboche's nonlinear kinematic hardening model extended by considering the effect of continuum damage mechanics employed to predict ratcheting. Lemaitre damage model [Lemaitre, J. and Desmorat, R. [2005] Engineering Damage Mechanics (Springer-Verlag, Berlin)] which is appropriate for low cyclic loading is used. Also the evolution features of whole-life ratcheting behavior and low cycle fatigue (LCF) damage of the tube are discussed. A simplified method related to the thin-walled tube under bending and internal pressure is used and compared well with experimental results. Bree's interaction diagram with boundaries between shakedown and ratcheting zone is determined. Whole-life ratcheting of thin-walled tube reduces obviously with increase of internal pressure.

Corner Strength of Investment Casting Shells

Abstract: During the investment casting process, the shell is subjected to high internal pressure and thermal stress, particularly during pattern removal and when pouring steel into the free standing ceramic shell. Most testing methods investigate the properties of the ceramic shell in flat regions while cracks typically form in the sharp corners and edge regions. The corners and edge regions have different structure and thickness when compared to flat regions and experience large mechanical stress during processing. In this study, experimental methods were combined with finite element modeling to predict failure stress in the internal corner regions of the shell. The model takes into consideration the mechanical properties of the ceramic shell to determine the stress developed during loading. The effect of shell porosity on stress concentration in sharp corners was evaluated. A general equation was developed to predict the force necessary for crack formation in the shell based on various geometric variables. The results from the model were experimentally verified and the failure stress in flat and corner regions of the shell were compared in order to develop an improved equation.

Wind-Induced Internal Pressures of Buildings with Multiple Openings

Abstract: Based on previous studies, it has been determined that internal pressures can contribute as much (or more) as the external pressures to the net pressures occasioned for low-rise buildings with a single dominant opening. However, the role of internal pressures, as experienced for cases with realistic geometry and multiple openings, is rarely investigated. As is known, low-rise buildings are susceptible to multiple- opening failures during strong windstorms, and the resulting changes in internal pressures are critical measures for tracking how the failure progresses from a localized level to a catastrophic level. Using the Wind Tunnel Laboratory located at Louisiana State University, by testing a typical 5:12 gable-roof residential-building model with 17 openings, a full picture of the internal pressure changes experienced during pro- gressive failure of multiple openings is obtained. The results indicated that (1) mean internal pressure coefficients estimated by two currently available, public hurricane-loss models werecloser to the minimum internal pressure coefficient measurements than themean internal pressure coefficient measurements at each stage of the multiple-opening failure; (2) ASCE guidelines underestimate the internal pressure for both par- tially enclosed and enclosed building types; and (3) Helmholtz resonance occurred near the theoretical resonance frequencies for two single opening cases for the current model with high damping. Based on these results, the flow resonance, dependent on the building geometry and the opening layout, should be considered to predict the potential wind-induced damage for low-rise buildings, and this is what is explored in this paper. DOI: 10.1061/(ASCE)EM.1943-7889.0000464. © 2013 American Society of Civil Engineers. CE Database subject headings: Internal pressure; Wind loads; Low-rise buildings; Aerodynamics; Openings. Author keywords: Internal pressure; Wind loads; Buildings; Low rise; Aerodynamics; Residential.

Analysis of an Aircraft Honeycomb Sandwich Panel with Circular Face Sheet/Core Disbond Subjected to Ground-Air Pressurization

Abstract: The ground-air pressurization of lightweight honeycomb sandwich structures caused by alternating pressure differences between the enclosed air within the honeycomb core and the ambient environment is a well-known and controllable loading condition of aerospace structures. However, initial face sheet/core disbonds intensify the face sheet peeling effect of the internal pressure load significantly and can decrease the reliability of the sandwich structure drastically. Within this paper, a numerical parameter study was carried out to investigate the criticality of initial disbonds in honeycomb sandwich structures under ground-air pressurization. A fracture mechanics approach was used to evaluate the loading at the disbond front. In this case, the strain energy release rate was computed via the Virtual Crack Closure Technique. Special attention was paid to the pressure-deformation coupling which can decrease the pressure load within the disbonded sandwich section significantly when the structure is highly deformed.

Structural Behavior of Corroded Steel Pipes Subject to Axial Compression and Internal Pressure: Experimental Study

Abstract: External corrosion is found in many onshore oil and gas pipelines, and corrosion is a major cause of structural failure of these pipelines. Onshore buried pipelines can be subjected to axial, bending, shear, and other complex loadings as a result of geotechnical movements and temperature variations. In addition, these pipes experience internal pressure from the fluids that they transport. Pipeline industry is concerned about the structural behavior and integrity of corroded pipelines when subjected to various loads and load combinations. Hence, structural behavior and failure conditions of corroded pipelines under various loads and load combinations need to be understood for safe operation of these field pipelines. A literature review did not reveal any studies that determined the structural behavior of corroded steel pipes when subjected to monotonically increasing axial compressive force with constant internal pressure. Therefore, an experimental study was completed to determine the structural behavior of X46 steel line pipe subjected to monotonically increasing axial compression and constant internal pressure as the geometry of corrosion and level of internal pressure change. This study shows that the axial load-carrying capacity reduces as the corrosion depth increases. However, this pipe is highly ductile and does not pose any threat to the structural integrity of the pipe when subjected to monotonically increasing axial deformation and constant internal pressure.

A Study on the Response of a Flexible Pipe to Combined Axisymmetric Loads

Abstract: In this work, the response of a 2.5″ flexible pipe to combined and pure axisymmetric loads is studied. A set of experimental tests was carried out and the results obtained are compared to those provided by a previously presented finite element model. The pipe was firstly subjected to pure tension. After that, the response to torsion superimposed with tension combined or not with internal pressure and the response to internal pressure combined with tension were investigated. In all these cases, the induced strains in the tensile armors were measured. Moreover, the axial elongation of the pipe was monitored in the pure tension test, whilst the twist of the pipe was measured when torsion was imposed and the axial reaction force was monitored when internal pressure was applied. The experimental results obtained agreed very well with the theoretical estimations indicating that the response of the pipe to tension and internal pressure is linear, whilst its response to torsion is nonlinear due to friction between layers.© 2013 ASME

Limit Analysis of Defect-Free Pipe Elbow Under Internal Pressure With Mean Yield Criterion

Abstract: With mean yield (MY) criterion, an analytical solution of the collapse load for a defect-free pipe elbow under internal pressure is first obtained. It is a function of ratio of thickness to radius t0/r0, strain hardening exponent n, curvature influence factor m and ultimate tensile strength. The collapse load increases with the increase of m, and it is the same as the burst pressure of straight pipe if m = 1 is assumed. The MY-based solution is compared with those based on Tresca, Mises and twin shear stress (TSS) yield criteria, and the comparison indicates that Tresca and twin shear stress yield criteria predict a lower bound and an upper bound to the collapse load respectively. However, the MY-based solution lies just between the TSS and Tresca solutions, and almost has the same precision with the Mises solution.

Unidirectional freezing freeze-thaw cycle triaxial apparatus and test method thereof

Abstract: The invention discloses a unidirectional freezing freeze-thaw cycle triaxial apparatus which comprises a pressure chamber, a mainframe, a stable air pressure source, a temperature control system, a water replenishing device and a test and data acquisition system, wherein the pressure chamber comprises an external pressure chamber and an internal pressure chamber; the upper part of the internal pressure chamber is provided with a sample cap formed by an upper box of the sample cap and a lower box of the sample cap; the bottom of the pressure chamber is provided with a base formed by an upper box of the base and a lower box of the base; the sample cap, the base and the external pressure chamber are respectively connected with a refrigerating machine by a heat insulation pipeline; the upper part of the pressure chamber is provided with a load power transmission shaft which passes through an upper cover of the pressure chamber and acts on the upper box of the sample cap; the base of the pressure chamber is connected with the water replenishing device by a pipeline; the mainframe is used for providing power for cutting a sample; and a temperature sensor arranged on the refrigerating machine and a displacement sensor and a load sensor which are arranged on the mainframe are connected with the test and data acquisition system The unidirectional freezing freeze-thaw cycle triaxial apparatus can realize the unidirectional freezing freeze-thaw cycle test under the conditions of low temperature and water supplement, and meanwhile can be used for testing the triaxial strength under the freeze-thaw cycle condition

Estimation device for cylinder intake air amount and internal egr rate in internal combustion engine

Abstract: An estimation device for a cylinder intake air amount and an internal EGR rate in an internal combustion engine is provided which is capable of making an estimation with a high degree of accuracy in a small number of adaptation constants. The estimation device calculates a volumetric efficiency corresponding value and the internal EGR rate based on an exhaust efficiency (a linear function of intake pipe internal pressure) which is an index indicating an amount of residual gas which is an exhaust gas after combustion remaining in the cylinder without being discharged from the cylinder to an exhaust pipe, and an intake efficiency (a linear function of intake pipe internal pressure) which is an index indicating an amount of air coming into the cylinder from the intake pipe excluding the residual gas.