Tightness Of Joints Research Articles

Creep analysis of bolted flange joints

In the petrochemical and nuclear industries, the difficulty in assessing the effect of creep on the tightening load of bolted flanged connections is recognized. Under high temperatures, the leak tightness of bolted joints is compromised due to the loss of the bolt load as a result of creep of not only the gasket and bolt materials but also the flange material. Apart from acknowledgment of this effect, there exists no established design calculation procedure that accounts for creep. This is because the relaxation of the bolt load and the corresponding loss of the gasket contact stress are not easy to assess analytically. The main objective of the work is the development of a simple analytical solution to the creep-relaxation problem encountered in bolted flange connections of the float type. Particular emphasis is put towards relaxation caused by the flange and bolt material creep. The validation of the methodology is carefully checked against the more complex 3D numerical FE method using different size flanges. Based on the creep constants of the different joint elements (bolt, flange and gasket), the implemented analytical method is shown to predict the bolt and gasket load relaxation with reasonable accuracy. In some flange cases, up to 70% of bolt load relaxation is found with both methods depending on the flange creep material and size.

Roughness parameters

Surface roughness evaluation is very important for many fundamental problems such as friction, contact deformation, heat and electric current conduction, tightness of contact joints and positional accuracy. For this reason surface roughness has been the subject of experimental and theoretical investigations for many decades. The real surface geometry is so complicated that a finite number of parameters cannot provide a full description. If the number of parameters used is increased, a more accurate description can be obtained. This is one of the reasons for introducing new parameters for surface evaluation. Surface roughness parameters are normally categorised into three groups according to its functionality. These groups are defined as amplitude parameters, spacing parameters, and hybrid parameters. This paper illustrates the definitions and the mathematical formulae for about 59 of the roughness parameters. This collection of surface roughness parameter was used in a new software computer vision package called SurfVision developed by the authors. In the package, these definitions were extended to calculate the 3D surface topography of different specimens.

Experimental Behavior of Full-Depth Precast Concrete Panels for Bridge Rehabilitation

An effective and economic design concept can be implemented for the rehabilitation of existing highway bridges and new bridge construction involving the application of full-depth precast or precast prestressed concrete panels that can be installed on concrete or steel beams. To verify the effectiveness of these structural systems, an experimental study was conducted on the proposed system to investigate the joints between adjacent precast panels, shear pocket connection between the precast panels and its supporting system to achieve full composite action, and the amount of concentric prestressing force that is needed in the deck system in the longitudinal direction to provide continuity and to secure the tightness of the transverse joints. The experimental objectives of the study included modeling a continuous prototype bridge with full-depth precast panels on steel stringers. These models were subjected to static and fatigue simulated American Association of State Highway and Transportation Officials truck loading. For the purpose of studying the effect of posttensioning, the bridge deck system for the first bridge model was not posttensioned longitudinally, while the decks for the second and third bridge models were posttensioned with a prestress level of 1.43 MPa (208 psi) and 2.62 MPa (380 psi), respectively. The effect of posttensioning was clearly evident in that first cracking initiated in the transverse joints near the central support (maximum negative moment region) for the nonposttensioned bridge model, while first cracking initiated in the central panel (over the central support) for the last two bridges. The applied load that caused the nonposttensioned bridge deck to crack was approximately one-third that of the posttensioned bridge deck models.

An investigation of the strength and tightness of joints based on a modified adhesive

The results are given of an investigation of the strength and tightness of joints in bar specimens and shells of silicate materials based on a modified epoxy adhesive. The promise of use of the studied adhesive for assembly of shells of silicate materials operating in contact with sea water is shown.

Comparative tests of the quality of joints of aluminum tubes with tube sheets made by expansion and axial press fitting

A method has been developed at the All-Union Scientific Research Technology Institute for Compressor Machinery Building for fastening tubes in a tube sheet by axial press fitting, which lacks the disadvantages of fastening tubes to tube sheets by expansion and welding. Comparative tests of joint quality of expansion and press fitting methods are made and the results indicate that the tightness and strength of joints made by the two methods are equivalent. All joint samples were tested for tightness by the mass spectrometric method. Taking into consideration the high quality of the axial press fitting joint, and the high effectiveness of the tool, it is desireable to fasten tubes in tube sheets by the axial press fitting method.

The determination of rock mass modulus variation with depth for weathered or jointed rock

Weathering or the variation in frequency and tightness of joints may result in an increase in mass modulus with depth for some rocks. This increase in modulus will continue until a depth is reached at which the rock behaves as a sound intact unit and the modulus will be relatively constant with depth below this point. In this paper, elastic solutions are presented for the deformation of such a rock mass due to a uniform or approximately rigid circular loading.Two procedures are described for determining the rock mass modulus profile from plate load test results. The first procedure uses the results from three plate tests to infer the variation in modulus with depth. The second procedure uses the measured variation in displacement with depth below a single plate to infer the mass modulus variation. The application of the two procedures is illustrated by a worked example and by consideration of a field case where the inferred modulus is shown to be in good agreement with alternative modulus variation data.

Nutrition, Weight Gain and Development of Hip Dysplasia

Thirty-one dogs from 5 litters with a high parental frequency of hip dysplasia were used in the investigation. Each litter was split in two groups, of which one was put on a high caloric intake, the other one on a low caloric intake. Each member of a group had a paired litter mate in the other group. The litter mates were paired on the basis of the result of a palpatory examination of the hip joints before 12 weeks of age. If possible, paired mates were of the same bodyweight at the time of palpation, and of the same sex. In the groups made up of pups from 3 of the litters, the protein intake was kept at an optimal level, regardless of the amount of calories given. It was found that hip dysplasia was more frequent, occurred earlier, and became more severe in the dogs with a rapid weight gain caused by increased caloric intake than in the dogs which had a low weight gain because of restricted feeding. The final diagnosis was closer correlated with feeding and weight gain than with tightness or laxity of the hip joints before 12 weeks of age.

Investigation of tightness of riveted joints with cover plates

Investigation of tightness of riveted joints with cover plates

Calibration of vibration pickups by the reciprocity method

The reciprocity theory for the relationship between mechanical force and velocity and electric current and voltage is presented for a linear electrodynamic vibration-pickup cali­ brator having a driving coil, a velocity-sensi ng coil, and a mounting table. The theory takes account of flexibility in the calibrator structure and in the coils, electric coupling be­ tween different parts of the same coil and between parts of one coil and parts of the other, and flexibility in the magnet structure. The theory shows what measurements are required in using a linear electrodynamic calibrator for the absolute calibration of vibration pickups. A description is given of the mechanical arrangement and electric circuitry used at the National Bureau of Standards in calibrating calibrators by the reciprocity method. A typical velocity-sensing-coil calibration curve is presented showing the effect of pickup mass on the calibration factor. Typical examples of measurement of calibration factor and me­ chanical impedance of pickups are also presented. Practical limitations of the reciprocity method due to nonlinearity resulting from lack of tightness of mechanical joints, resonance effects, amplitude effects, etc., are discussed.

Closure to “Discussion of ‘Note on the Tightness of Expanded Tube Joints’” (1948, ASME J. Appl. Mech., 15, pp. 176–177)

Closure to “Discussion of ‘Note on the Tightness of Expanded Tube Joints’” (1948, ASME J. Appl. Mech., 15, pp. 176–177)

Note on the Tightness of Expanded Tube Joints

Abstract A simple theoretical evaluation of the conditions conducive to maximum tightness of a tube joint is presented. The residual pressure between tube and plate, which can be considered as a measure of the tightness, possesses a maximum at certain tube dimensions. If tube and plate are of the same material, the tightness increases with increasing ratio of outside to inside diameter of the tube, up to a ratio of 1.4. If the tube is made from a metal sufficiently stronger than that of the plate, the residual pressure becomes larger, possessing a maximum at a ratio of 1.65 of the tube diameters.

The Holding Power and Hydraulic Tightness of Expanded Tube Joints: Analysis of the Stress and Deformation

Abstract The expanding process used for making the tubes of boilers tight and in other applications is idealized to form a problem in the theory of plasticity. This problem is solved in order to find out how far the factors taken into account in this theory are adequate to explain the results obtained in tests, mainly those reported in the companion paper of Grimison and Lee (19). The pressure left between the tube and plate or seat, which gives it tightness and contributes to its strength, is the principal object of calculation. Its variations with the yield stresses of tube and plate material, with degree of expanding, and with the thickness of the plate, are obtained in graphical form. Numerical comparison with tests is made for six joints, with fair agreement in five, the theoretical values being within 12 per cent. All are on the low side, and this is to be expected from the fact that the theory disregards strain-hardening, stress in the direction of the tube axis, and possible differences between expanding by a three-roller tool and expanding by uniform pressure within the tube.

Suitability of Indian Fire Clays for Steel Ladle Brick

Refractory brick used in India for lining steel ladles although made of Fireclay of high Alumina content do not give the same service as some of the bricks made from low grade fireclay in some foreign countries. Service conditions prevalent in a ladle has been discussed. Analysing the conditions, it teas considered that high ‘After-Contraction’ of the Indian Ladle bricks was the cause of the inferior service given by these. Two brands of bricks were specially made with reduced ‘After-Contraction’ and tried under actual operating conditions. Laboratory and service test data on the above two bricks and the brand of brick ordinarily used are given. From these it was apparent that the bricks with low ‘After-Contraction’ were superior to the commonly used brick. By lining ladles with these specially made brick, it was possible to take more than one and half times as many casts as taken by ladles with ordinary bricks. Some of the other noticeable features in the former ladles were:—(a) Tightness of joints, (b) Uniform wear of bricks and absence of pronounced attack at the joints, (c) Comparatively Use damage by “Skulling“, (d) The ease with which such skulls could be removed.

The Resistance to Relaxation of Materials at High Temperature

Abstract Relaxation tests at high temperature give direct information on the permanent tightness of bolted joints and shrinkage assemblies. They also give direct measurements of the effectiveness of strain-relief anneals. Indirectly they give, in relatively short time and small furnace space, reliable information on long-time constant-stress behavior although direct computation of either type of performance from the other is uncertain. In relaxation tests, total strain is definitely limited, whereas, creep rates based on constant-stress tests may, but do not necessarily, correspond to excessive amounts of strain, thus giving too optimistic indications of strength. Although advantageous, relaxation tests do not take the place of constant-stress tests. A simple formulation for relaxation is given which holds good for considerable periods although rather sudden changes of trend suggest the possibility of physical changes in the material which are not easily predictable in advance. Test results are given on six materials at various temperatures.

An Experimental Research on Riveted Joints

An experimental research on riveted single butt strap joints was carried out at the Kure Naval Dockyard.The work was directed to the study, under tensile forces, of the ultimate strength, water tightness and slip phenomena of joints. Three grades of rivets were used, respectively mild steel, high tensile steel and high elastic limit steel.These combinations permitted a study to be made of the effect upon the ultimate strength and behaviour of joints.In addition tests were made on specimens containing three strakes to ascertain the effect, upon the behaviour of joints, of laying plating adjacent to the joint.