Showing papers on "Internal pressure published in 1983"

The performance and causes of failure of polyethylene pipes subjected to constant and fluctuating internal pressure loadings

Abstract: Three different pipe-grade polyethylenes, in the form of one large and three small diameter pipe systems, have been tested at elevated temperatures, using constant and fluctuating internal pressure loadings that resulted in brittle fractures. The behaviour under fatigue of two of the three types of small diameter polyethylene pipes was substantially described by a cumulative damage model, whilst the third exhibited a fatigue weakness, an observation not previously reported. The performance of the large diameter pipes under fatigue was dominated by the presence of large voids in the pipe wall that arose from incorrect processing and resulted in premature failure. The sites of crack initiation in one material grade of the small diameter systems were examined in detail. In particular the size, position and composition of particles initiating fracture were determined. The maximum particle size on the fracture surface of the pipe was found to correlate reasonably well with a measure of pipe lifetime, as predicted by a fracture mechanics approach, and indicated that the lifetime of this one type of polyethylene pipe was dependent on the size of the inclusions initiating fracture.

Internal Pressure of Multi‐Room Buildings

Abstract: The Bernoulli equation approach for predicting the variation of internal pressure induced by wind in a single‐room building with a single opening is extended to multi‐room buildings of any number of openings. Examples are given to illustrate this new general approach. The result shows that following the breakage of a windward window during a windstorm, the internal pressure of a multi‐room building oscillates in a manner similar to that in a set of interconnected Helmholtz oscillators.

Stress-induced magnetization changes of steel pipes--Laboratory tests, Part II

Abstract: Magnetometer surveys above gas pipelines have shown stress-induced magnetic anomalies at pipe bends. This suggests a technique for noninvasive monitoring of stress in pipelines and other ferromagnetic structures. Previous laboratory measurements of the external magnetic field changes due to single bending and internal pressure cycles on 110 mm diameter steel pipes demonstrated that stress and magnetic hysteresis effects were important. The stress-induced changes in magnetization produced during multiple cycles of elastic bending and internal pressure for pipes which have been demagnetized and then magnetized to simulate magnetic inspection of a real pipeline is reported. The stress-induced changes can be divided into relatively large irreversible changes occurring principally during initial stressing and smaller reversible changes occurring during any stress cycle. This is in agreement with Jiles' and Atherton's recent theory of the effect of stress on magnetization which shows that the application of stress to a ferromagnet shifts its magnetization towards the anhysteretic which is also slightly stress dependent. The significance of results to applications is indicated.

Influence of Radial Compressive Stress Owing to Pressure On the Failure Modes of Composite Tube Specimens

Abstract: The failure behaviour of unidirectional laminae in σ1 - -σ2 stress space has been studied using thin wall hoop-wound tubular specimens. σ 1 was generated by internal pressure and -σ2 by axial compression. It was found that the radial compressive stress -σ 3, due to internal pressure, has a profound effect on the failure behaviour in the range where failure occurred by matrix fracture. A model is presented for the effect of the radial compressive stress using a matrix failure criterion. The experimental data agreed reasonably well with the predictions of failure stresses based on this model. Optical microscopy revealed that shear deformation preceded final fracture in agreement with the model.

Viscoelastic shear thinning of liquids. A molecular-dynamics study

Abstract: A molecular-dynamics investigation into the microscopic response of simple liquids subjected to severe shearing conditions is discussed. The quantitative behaviour of a model Lennard-Jones liquid and experimental data on more complicated molecular fluids at high levels of stress are strikingly similar, provided appropriate adjustments of characteristic relaxation time-scales are made.The simulations give insights into the structural origin of material failure at high shear stresses and reveal, at high pressures, a restructuring of the medium into layers, which permits easier flow and hence reduces its viscosity. This change is also manifest in an increase of internal pressure (at constant volume) and a decrease in low-frequency shear rigidity modulus and thermal conductivity.Associated temperature distributions in the non-linear region of viscosity are consistent with macroscopic continuum theory, suggesting that the thermal effects due to shear are essentially decoupled from any parallel structural changes.

Elastic-plastic stress analysis of a cracked thick-walled cylinder

Abstract: The boundary integral equation (BIE) method for two-dimensional elastic-plastic stress analysis is applied to an internally pressurized thick-walled cylinder containing a radial crack. Two different types of material are considered, namely, an elastic-perfectly plastic material and a work-hardening material. The loading conditions applied include the case when the internal pressure also acts on the crack faces, and the case when it does not. Results are presented showing the plastic zone development in the cylinder and the variations of the fracture mechanics parameter, the J line integral, with increasing internal pressure.

Improvements in synthetic vascular grafts and methods of manufacturing such grafts

Abstract: A synthetic vascular graft of internal diameter in the range of 0.1 mm to 20 mm and wall thickness between 0.075 mm and 2.0 mm is preferably made by electrostatic spinning of polymeric material. Under an elongation of between 5% and 25% over its unstressed state, the change in internal pressure from a first pressure to a second pressure, the difference between the first and second pressures lying in the range between 20 mm Hg and 75 mm Hg, undergoes a change in internal diameter substantially equal to the change in internal diameter experienced when a corresponding natural artery stretched to an extend experienced in vivo is subjected to the same change in internal pressure. The graft is made by electrostatically spinning an organic polymer material.

Stress Intensity Factors for Radial Cracks in a Pre-Stressed, Thick-Walled Cylinder of Strain-Hardening Materials

Abstract: : A simple method which combines the weight function technique and finite element results is used to obtain mode I stress intensity factor solutions for radially cracked cylinders subjected to a high internal pressure. The method is especially effective for cylinders having residual stresses due to a manufacturing pre-stress process to increase the maximum pressure the cylinder can contain, and to improve the cylinder's useful life against fatigue and fracture. The method is quite general for various assumptions involving the plastic stress-strain relations, the yield condition, the strain-hardening, and the compressibility of the cylinder material.

Some boundary integral equation solutions for three-dimensional stress concentration problems

Abstract: The boundary integral equation (BIE) method for three-dimensional linear, elastic stress analysis is applied to some stress concentration problems associated with transverse circular holes in either hollow or solid circular cylinders subject to axial tension or torsion, also offset-oblique holes in cylinders subject to internal pressure. Satisfactory agreement is obtained with some previously published experimental results, although computed maximum stress concentration factors are generally higher than those obtained experimentally. The BIE method is shown to be a very useful tool for solving three-dimensional problems of engineering stress analysis.

Structure of aqueous electrolyte solutions. Thermodynamic internal pressure

Abstract: The thermodynamic internal pressures of aqueous electrolyte solutions have been analysed using three models (the Tammann–Tait–Gibson, TTG, the orientation defect and the non-interacting homomorph, NIH) together with the infrared (i.r.) and dielectric structural temperatures. The effect of ionic volumes is to change water–water interactions. This leads to a change (increase or decrease) in the internal pressure of the water of pww bar. The ionic-charge effects cause an increase in pressure of (pe–plr) bar, where pe is the TTG effective pressure and plr is the long-range pressure (deriving from forces proportional to z2/r and to z2). pel(a component of pe and arising from the electrical deformation of the water molecules) plus pww are mainly responsible for the changes in pressure associated with the hydrogen-bond energy. The pressure changes associated with second cosphere events can be ascribed to intermolecular forces and small changes in the free OH.

Closure safety device

Abstract: A pressure activated safety device includes a body structure defining an internal chamber having a partition movably disposed within the chamber. Pressure from a pipeline, pressure vessel, etc., acts upon the partition and positions it at a locking position preventing a venting seal from being released. A seal releasing element is movable relative to the body structure and is manually forced into an unlocking position against the bias of pressure acting upon the partition. The partition is pressure responsive such that it is manually movable from the locking position only upon the occurrence of a negligible pressure condition within the pressure chamber, thus providing for movement of a mechanical object only under an internal pressure condition that renders the apparatus safe.

Thermal Pressure Coefficient, Internal Pressure and Solubility Parameter of Hard Sphere Fluids

Abstract: The thermal pressure coefficient (rv) is evaluated for nine hard sphere liquids at wide range of temperature with the help of Carnahan-Starling equation of state simply by knowing the molar volume and the diameter of the liquids. The latter parameter is computed by a semiempirical method consisting of surface tension and critical temperature data which has been derived on the basis of Lennard-Jones potential. Internal pressure (JI). solubility parameter (<5) and Hildebrand constant (n) were also calculated V or these liquids. Plots of Tv versus T, n versus I and — / v versus T/Tc reveal important information R about the liquid state. Results were compared with the available literature values and fairly good agreement is obtained.

On the problem of two coplanar cracks inside an infinite isotropic elastic solid

Abstract: A method is proposed for the approximate evaluation of normal displacements and normal stresses on the plane of two coplanar cracks located inside an infinite isotropic elastic solid and subjected to normal internal pressure. The formulation results in a single integral equation for the unknown normal stresses on the plane of the cracks. Numerical results are given for the stress intensity factor KI of two coplanar circular cracks and two coplanar elliptical cracks opened up under a uniform internal pressure.

Finite Element Results of Pressurized Thick Tubes Based on Two Elastic- Plastic Material Models

Abstract: : The loading and unloading problems in thick tubes subjected to uniform internal pressure have been analyzed with the ADINA finite element code. The elastic-plastic materials are modeled by two strain-hardening rules- isotropic and kinematic. The von Mises yield condition, the associated flow theory, and a numerical results of the stresses and displacements for thick tubes with different wall ratios are obtained as functions of loading history. A comparison of numerical results based on two material models is made.

Windows and radomes

Abstract: A window assembly for a flight vehicle comprises a window member 4 of material transmissive to electro- magnetic radiation and which in use will be subject to aerodynamic pressure loads but whose thickness is such that the window member has insufficient structural stiffness to withstand these loads. The window member 4 is secured around its periphery to form a chamber which is pressurised via source 7 to provide a fluid pressure support for the window member against such pressure loads. A support member 8 may be provided either exteriorly or interiorly or both of the window member 4 against which the window member is urged in use. Fluid pressure support may be by means of an internal pressure source, or by means of ram air pressure.

Aqueous solutions. 1. Structural thermodynamic internal pressure of water

Abstract: The 3-D hydrogen bonding gives water its unique structural properties (eg, the configuration can vary on a molecular level even at constant volume) and gives rise to an internal structural pressure, p/sub s/ This pressure provides a link between macroscopic and microscopic properties, p/sub s/ has been analyzed in terms of dielectric correlations and relaxations and compared with related quantities from an infrared orientation-defect (OD) model In the limit, as p/sub s/ approaches zero, the water structure appears to approach that of glassy water 3 tables

Method for recovering heat by organic heat-transmitting medium oil

Abstract: PURPOSE:To constantly maintain the internal pressure of a heat-recovering heat exchanger at the atmospheric pressure level, by a method wherein a pressure rise is easily relieved even when the temperature of a heat-transmitting medium oil is raised to or above the boiling point of the oil at the time of stagnation of the oil. CONSTITUTION:The heat-recovering heat exchanger 2 placed at a rising pipe 1 for a coke furnace is connected to a heat-radiating heat exchanger 3 by a pipe 4, and a pump 6 is placed in an intermediate part of the pipe 4. An expansion tank 7 is placed in a pipe 8 branched from an appropriate part of the pipe 4 which connects the heat exchanger 2 with the pump 6. In the tank 7 in which the liquid level does not exceed the level of the uppermost end 10 of heat-transmitting surfaces of the heat exchanger 2, an overflow pipe 9 is placed at the same level, and the liquid surface in the tank 7 is opened to the air. Accordingly, in case of emergency wherein the pump 6 is stopped due to the interruption of power supply or the like, the heat exchanger is connected to the tank 7, and since the liquid level in the tank 7 is set to be not higher than the level of said uppermost end 10, the free surface of the heat-transmitting medium oil is always maintained at the atmospheric pressure, so that a pressure rise due to a rise of the temperature of the oil can be prevented in any case.

Process for pressure-controlled H2/O2 recombination

Abstract: In the catalytic combustion of H2 and O2 in a recombination reactor, the gases are fed alternately to the reactor via inlet valves which are designed such that they always open at one internal pressure P1 of the reactor, but close at different internal pressure p2/H or p2/O , so that the admitted rates of H2 and O2 are in a ratio of 2:1 The initial filling of the reactor with one of the gases (for example H2) as a purging gas and the first feeding of the other gas (O2) at a rate exceeding the equivalence to the first gas have the consequence that, during the subsequent recombination, residue of the fed gas remains, which in turn is overcompensated by the next gas feed and is recombined with overstoichiometry of this gas The constant repetition results in a continuous gas consumption which, in its course in time, oscillates between an overstoichiometry of O2 and an overstoichiometry of H2

Manufacture of heat collector

Abstract: PURPOSE:To restrain deformation in a manufacturing method that makes linear welding two overlapped metallic plates by a laser beam, applies internal pressure between the two metallic plates nd forms flow passages by swelling the parts between linearly welded parts, by applying internal pressure between rigid body separated from each other. CONSTITUTION:After linear welding two overlapped metallic plates 2, 3 by a laser beam, the plates are inserted between a rigid body 14 having faces 13 separated from each other. After sealing the outlet 6, high pressure fluid is introduced from the inlet between the two metallic plates 2, 3 and the metallic plate 2, 3 between weld lines 7, 10 are bulged out to form passages 11 of heat medium. At this time, the rigid body 14 restrains excessive bulging to make passages desired size and shape.

Pressure-to-frequency transducer

Abstract: A vibratable element whose resonant frequency changes in accordance with an external source of variable applied pressure, has an inner cavity in fluid communication with the source of applied pressure, so that variations therein produce corresponding changes in the internal pressure of the cavity Increases in this internal pressure cause the flexible walls surrounding the cavity to expand outwardly, thereby increasing the mechanical stiffness of the element The increased stiffness produces a corresponding increase in the resonant frequency Conversely, a decrease in pressure allows the walls to slacken and reduce the overall stiffness of the element A linear relationship exists between changes in applied pressure and changes in the resonant frequency, over an appreciable range of pressures An optical scheme detects the frequency, and conventional electronics correlate the frequency to the corresponding pressure, or to another physical variable represented by the applied pressure

Liquid level detecting method

Abstract: PURPOSE:To improve extensive usability, by detecting the position of a liquid level by the increase in internal pressure; when a gas is supplied into a tubular body, which has a gas supplying means and a gas pressure detecting means and is provided with a hole at the lower end, and the lower end approaches the liquid or it is contacted with the liquid. CONSTITUTION:A cylinder control part 10 is operated. A compressed gas is sent into a cylinder 7 from a cylinder gas supplying port 11. A piston 6 are a tubular body 4 are lowered by said pressure. At this time, the gas is exhausted from a lower end hole 3 and a gas pressure measuring hole 2 of the tubular body 4. The tubular body 4 is gradually lowered. When the lower end approaches the liquid or it is contacted with the liquid, the pressure that is applied to the hole 3 is increased. Therefore, the amount of the gas exhausted from the gas pressure measuring hole 2 is increased. The pressure of the gas exhausted from the measuring hole 2 is measured by a gas pressure detector 12. When said pressure becomes a preset value or more, the point is made to be the liquid level.

Method for estimating life of high temperature fluid container

Abstract: PURPOSE:To estimate the life of a high temperature fluid container such as turbine casing accurately, by measuring the temperature and pressure of high temperature fluid and the temperature at the evaluating point of the container, computing the quantity of damage based on breaking dynamics, and comparing the result with allowable quantity which is caluculated in advance. CONSTITUTION:In order to measure the life of casing of a high pressure stage steam turbine and the like, steam pressure and temperature of main steam, high pressure exhaust, and the like are detected by a pressure detecting device 13 and a temperature detecting device 12. The metal temperature of the casing is measured by a thermocouple 14. They are diagnosed in 3 routes through an internal pressure stress operator 18, a thermal stress operator 19, and an adder 20. One is compared with a reference value 22 (allowable stress) in a comparator 21, and the result is judged by a judging device 23 and displayed on a warning display device 24. Stress and temperature are determined by an analyzer 28 based on a time versus stress relation-ship and temperature curve diagram 35. Damage evaluation computation is performed by an operator 30 based on creep rupture curves 36. An analyzer 25 determines the stress amplitude based on a time versus stress curve diagram 37. Damage values are obtained by an operator 27 based on a fatigue strength curve diagram 38. Then the remaining life is determined based on the total damage value.

Valve shaft sealing device of carburetor for internal- combustion engine with supercharger

Abstract: PURPOSE:To perform good sealing of a valve shaft in a well slidable state with bearing parts of a carburetor main unit supporting the valve shaft, by providing annular grooves in the periphery of the valve shaft and supplying pressurized air in the delivery side of a supercharger to said annular grooves. CONSTITUTION:Annular grooves 54A, 54B, at a face-to-face position to internally peripheral surfaces of bearing parts 48 in the inside of sealing members 52, are formed to a valve shaft 46 in a carburetor main unit 42. Though a pressurized mixture in an intake passage 44 tends to leak out to the atmosphere from between the peripheral surface of the valve shaft 46 and the internally peripheral surface of the bearing parts 48, the annular grooves 54 are provided and pressurized air is fed from a surge tank (not shown in the drawing), and internal pressure in the annular grooves 54 is higher than internal pressure of the intake passage 44. Accordingly, the pressurized mixture between the valve shaft 46 and the bearing parts 48 is pressed back into the intake passage 44 never to leak out to the outside. Further the pressurized air in the annular grooves 54 flows through the sealing members 52, even if slightly leaked out to the atmosphere, a bad influence is almost not caused, and the necessity for firmly pressing the sealing members 52 to the valve shaft 46 is eliminated, then slide resistance can be also decreased.