Some Applications of Plasticity Theory to the Statics of Syntactic Foam

1971 ◽  
Vol 38 (1) ◽  
pp. 23-29 ◽  
Author(s):  
J. A. DeRuntz
Keyword(s):  
Experimental Data ◽  
Composite Material ◽  
Syntactic Foam ◽  
External Pressure ◽  
Plasticity Theory ◽  
Failure Condition ◽  
Inhomogeneous State ◽  
Collapse Pressure ◽  
State Of Stress ◽  
Further Development

A failure condition recently proposed for the composite material syntactic foam is applied to the inhomogeneous state of stress which occurs in a layered sphere exposed to external pressure. The sphere is composed of syntactic foam which surrounds an assumed perfectly elastic hollow inclusion of higher strength than the syntactic foam. In addition to the establishment of the stress level at which the syntactic foam begins to crush, an analysis similar to that of perfect plasticity theory is carried out to find the ultimate collapse pressure of the syntactic foam. The results are found to compare favorably with experimental data. This problem is of importance in the further development of buoyancy materials for deep submergence vehicles.

Experimental Study on the Effect of Axial Tension Load on the Collapse Strength of Oilwell Casing

1982 ◽  
Vol 22 (05) ◽  
pp. 609-615 ◽  
Author(s):  
T. Kyogoku ◽  
K. Tokimasa ◽  
H. Nakanishi ◽  
T. Okazawa
Keyword(s):  
Experimental Data ◽  
Theoretical Analysis ◽  
Testing Machine ◽  
External Pressure ◽  
Tension Stress ◽  
Plastic Collapse ◽  
Collapse Pressure ◽  
Axial Tension ◽  
Collapse Strength ◽  
Tension Load

Abstract This paper discusses a newly developed collapse testing machine that permits investigation of practical performances of oilwell casings. Although a theoretical performances of oilwell casings. Although a theoretical analysis has shown that "axial tension stress has no effect on collapse pressure in the elastic case," this theory is not applied to the design of casing string because of lack of useful experimental data or authorized recommendation. To investigate the effect of axial tension load, full-size commercial casings have been tested under combined loading of axial tension load and external pressure. From the experimental results, the theory mentioned was proved in the case of so-called high-collapse casing, which has been used widely in recent years. Also shown is the applicable d/h range, which is wider than API's elastic collapse range. If the results of this experiment were applied to the design of a casing program, an economical and safe one could be obtained. program, an economical and safe one could be obtained. Introduction Recently, improved drilling techniques have permitted deeper and deeper oil and gas wells. As well depth increases, steel pipes for well casings receive greater external pressure and axial tension load because of the weight of the casing string. High-collapse casing, which has higher collapse strength per unit weight, has become easily available. To select and to design casing for such wells properly and economically, estimating collapse strength of the casing under axial tension load is very important. Much research and many experiments concerning collapse problems on casing, drillpipe, and tubing has been conducted by 1939. A theoretical analysis showed that axial tension stress lowers the collapse pressure in the case of plastic collapse and that axial tension stress has no effect on collapse pressure in the elastic case. Although collapse tests under axial tension load simulating oilwell casing in service were conducted on 2-in.-OD tubings, the theory for the effect of axial tension stress in the elastic collapse had not been proved sufficiently. There are few published experimental proved sufficiently. There are few published experimental data on collapse strength under axial tension load. In 1968, API summarized the collapse data and showed the formulas for collapse pressure and for collapse pressure under axial tension stress in the case of plastic collapse. The purpose of our study is to show how the collapse strength of commercial casings with large OD's behaves under the axial tension load, especially in the case of elastic collapse. To test the large-size casings, a multipurpose collapse testing machine that can simulate the service condition of oilwell casing has been developed. Statement of the Problem The collapse strength of casings under combined external pressure and axial tension load may be calculated from pressure and axial tension load may be calculated from Ref. 6's Formula 1.1.5.1: ....................(1) SPEJ p. 609

Clamped torispherical shells under external pressure — some new results

1988 ◽  
Vol 23 (1) ◽  
pp. 9-24 ◽  
Author(s):  
J Blachut ◽  
G D Galletly
Keyword(s):  
Failure Mode ◽  
External Pressure ◽  
Spherical Cap ◽  
Geometric Imperfections ◽  
Collapse Pressure ◽  
Modes Of Failure ◽  
Shell Buckling ◽  
Bifurcation Buckling ◽  
Initial Geometric Imperfections ◽  
The One

Perfect clamped torispherical shells subjected to external pressure are analysed in the paper using the BOSOR 5 shell buckling program. Various values of the knuckle radius-to-diameter ratio ( r/D) and the spherical cap radius-to-thickness ratio ( Rs/ t) were studied, as well as four values of σyp, the yield point of the material. Buckling/collapse pressures, modes of failure and the development of plastic zones in the shell wall were determined. A simple diagram is presented which enables the failure mode in these shells to be predicted. The collapse pressures, pc, were also plotted against the parameter Λs (√( pyp/ pcr)). When the controlling failure mode was axisymmetric yielding in the knuckle, the collapse pressure curves depended on the value of σyp, which is unusual. However, when the controlling failure mode was bifurcation buckling (at the crown/knuckle junction), the collapse pressure curves for the various values of σyp all merged, i.e., they were independent of σyp. This latter situation is the one which normally occurs with the buckling of cylindrical and hemispherical shells. A limited investigation was also made into the effects of axisymmetric initial geometric imperfections on the strength of externally-pressurised torispherical shells. When the failure mode was axisymmetric yielding in the knuckle, initial imperfections of moderate size did not affect the collapse pressures. In the cases where bifurcation buckling at the crown/knuckle junction occurred, small initial geometric imperfections at the apex did not affect the buckling pressure, but axisymmetric imperfections at the buckle location did influence it. With the other failure mode (i.e., axisymmetric yielding collapse at the crown of the shell), initial geometric imperfections caused a reduction in the torisphere's strength.

A Simple Procedure for the Prediction of the Collapse Pressure of Pipelines With Narrow and Long Corrosion Defects: Uncertainty and Sensibility Analysis

2018 ◽  
Author(s):  
Nara Oliveira ◽  
Theodoro Netto
Keyword(s):  
Simple Procedure ◽  
Experimental Tests ◽  
External Pressure ◽  
Experimental Program ◽  
Small Scale ◽  
Test Results ◽  
Collapse Pressure ◽  
Operational Conditions ◽  
Sensibility Analysis ◽  
Corrosion Defects

The collapse pressure of pipelines containing corrosion defects is usually predicted by deterministic methods, either numerically or through empirical formulations. The severity of each individual corrosion defect can be determined by comparing the differential pressure during operation with the estimated collapse pressure. A simple deterministic procedure for estimating the collapse pressure of pipes with narrow and long defects has been recently proposed by Netto (2010). This formulation was based on a combined small-scale experimental program and nonlinear numerical analyses accounting for different materials and defect geometries. However, loads and resistance parameters have uncertainties which define the basic reliability problem. These uncertainties are mailyrelated to the geometric and material parameters of the pipe and the operational conditions. This paper presents additional experimental tests on corroded pipes under external pressure. The collapse pressure calculated using the equation proposed by Netto (2010) is compared with this new set of experiments and also with test results available in open literature. These results are used to estimate the equation uncertainty. Finally, a sensitivity analysis is performed to identify how geometric parameters of the defects influence the reduction of collapse pressure.

An Exit Burr Model for Drilling of Metals

2000 ◽  
Vol 123 (4) ◽  
pp. 562-566 ◽  
Author(s):  
L. Ken Lauderbaugh Saunders ◽  
Craig A. Mauch
Keyword(s):  
Experimental Data ◽  
Stress State ◽  
Temperature Effects ◽  
Material Removal ◽  
Burr Formation ◽  
Failure Condition ◽  
Formation Model ◽  
Varying Thickness ◽  
Exit Burr ◽  
Thrust Forces

The mechanics of the formation of exit burrs for drilling metals are analyzed. A burr formation model is developed where the material in front of the drill is modeled as an axi-symmetric, circular plate of varying thickness. The drilling thrust forces are distributed as a pressure along the top surface of this plate. The stress state is then calculated. Material removal continues until a failure condition is reached. At the point of failure of the plate the remaining material is bent out to form the burr. The model also includes temperature effects. Experimental verification was conducted on 2024-T351 aluminum and on 7075-T561 aluminum. Two types of drill geometry were considered. The experiments were conducted with feeds from 0.05 to 0.35 mm/rev. The model accurately predicts the experimental data.

Heavy Gauge UOE Pipe With Improved Compressive Strength for Offshore Pipeline

2012 ◽  
Author(s):  
Nobuyuki Ishikawa ◽  
Hitoshi Sueyoshi ◽  
Kimihiro Nishimura ◽  
Osamu Yamamoto ◽  
Akihiko Tanizawa ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Bauschinger Effect ◽  
External Pressure ◽  
Accelerated Cooling ◽  
Second Phase ◽  
Fundamental Study ◽  
Soft Phase ◽  
Collapse Pressure ◽  
Bainitic Microstructure ◽  
Line Process

Offshore gas pipeline development has been expanding toward deeper water region that requires pipes to have strong resistance against collapse by external pressure. Collapse pressure is mainly dominated by pipe roundness and compressive strength. In order to improve compressive strength, it is quite important to understand the Bauschinger effect caused by cyclic deformation during pipe forming. Compressive strength is reduced by the Bauschinger effect since compression in the circumferential direction is applied after the pipe expansion. Therefore, prevention of Bauschinger effect is an important issue for improving compressive strength of pipes. In this paper, the effect of microstructure on the Bauschinger effect was investigated. It was proved that microstructure that consists of a hard second phase shows a large strength reduction in reverse loading, since a mixed microstructure with soft phase and hard phase enhances the Bauschinger effect. In order to obtain homogeneous bainitic microstructure, advanced plate production technology, where heat treatment on-line process (HOP) is applied after accelerated cooling, was developed. The steel produced by HOP process exhibits a fine bainitic microstructure with very low amount of hard second phase such as MA constituent. It was demonstrated that the trial produced pipe with HOP process has a higher compressive strength than conventional pipes. In addition to the fundamental study on compressive strength, further investigations were conducted to optimize other material properties for offshore linepipe, such as DWTT property, resistance to hydrogen induced cracking and HAZ toughness to comply with DNV requirements. Production tests of Grade X65 linepipe with the 38mm WT and 876mm OD was carried out. Material and mechanical properties of these heavy gauge linepipes were introduced.

Buckling Design of Imperfect Welded Hemispherical Shells Subjected to External Pressure

1991 ◽  
Vol 205 (3) ◽  
pp. 175-188 ◽  
Author(s):  
G D Galletly ◽  
J Blachut
Keyword(s):  
Experimental Information ◽  
External Pressure ◽  
Design Stage ◽  
Arc Length ◽  
Spherical Shells ◽  
Geometric Imperfections ◽  
Collapse Pressure ◽  
Buckling Resistance ◽  
Initial Geometric Imperfections ◽  
Hemispherical Shells

Welded hemispherical or spherical shells in practice have initial geometric imperfections in them that are random in nature. These imperfections determine the buckling resistance of a shell to external pressure but their magnitudes will not be known until after the shell has been built. If suitable simplified, but realistic, imperfection shapes can be found, then a reasonably accurate theoretical prediction of a spherical shell's buckling/collapse pressure should be possible at the design stage. The main aim of the present paper is to show that the test results obtained at the David Taylor Model Basin (DTMB) on 28 welded hemispherical shells (having diameters of 0.75 and 1.68 m) can be predicted quite well using such simplified shape imperfections. This was done in two ways. In the first, equations for determining the theoretical collapse pressures of externally pressurized imperfect spherical shells were utilized. The only imperfection parameter used in these equations is δ0, the amplitude of the inward radial deviation of the pole of the shell. Two values for δ0 were studied but the best overall agreement between test and theory was found using δ0 = 0.05 ✓ (Rt). This produced ratios of experimental to numerical collapse pressures in the range 0.98–1.30 (in most cases the test result was the higher). The second approach also used simplified imperfection shapes, but in conjunction with the shell buckling program BOSOR 5. The arc length of the imperfection was taken as simp = k ✓ (Rt) (with k = 3.0 or 3.5) and its amplitude as δ0 = 0.05√(Rt). Using this procedure on the 28 DTMB shells gave satisfactory agreement between the experimental and the computer predictions (in the range 0.92–1.20). These results are very encouraging. The foregoing method is, however, only a first step in the computerized buckling design of welded spherical shells and it needs to be checked against spherical shells having other values of R/t. In addition, more experimental information on the initial geometric imperfections in welded spherical shells (and how they vary with R/t) is desirable. A comparison is also given in the paper of the collapse pressures of spherical shells, as obtained from codes, with those predicted by computer analyses when the maximum shape deviations allowed by the codes are employed in the computer programs. The computed collapse pressures are frequently higher than the values given by the buckling strength curves in the codes. On the other hand, some amplitudes of imperfections studied in the paper give acceptable results. It would be helpful to designers if agreement could be reached on an imperfection shape (amplitude and arc length) that was generally acceptable. Residual stresses are not considered in this paper. They might be expected to decrease a spherical shell's buckling resistance to external pressure. However, experimentally, this does not always happen.

Exploratory Study on Engineering Ceramics Pressure Hulls for Deep-Sea Submergence Services

2005 ◽  
Vol 39 (3) ◽  
pp. 49-55 ◽  
Author(s):  
Yusuke Yano ◽  
Shinichi Takagawa
Keyword(s):  
Deep Sea ◽  
Syntactic Foam ◽  
Structural Materials ◽  
External Pressure ◽  
Engineering Ceramics ◽  
Practical Applications ◽  
Collapse Strength ◽  
Reinforced Plastic ◽  
Pressure Tests ◽  
The Relationship

An underwater vehicle for deep-sea operation should be as light as possible; therefore, development of premium structural materials such as titanium alloy, glass, and carbon-fiber-reinforced plastic (CFRP) for external pressure hulls has been ongoing. Engineering ceramics is one of the candidate materials, and the study of engineering ceramics has been underway for many years; however practical applications have been limited.The main purpose of this study is to establish the methodology of fabrication of ceramics pressure hulls for deep-sea submergence services. As the first step, prototypes of the spherical shells were fabricated from engineering ceramics, and their local radii of curvatures and wall thickness were precisely measured. In addition to these measurements, the strain on hemispheres and their collapse strength were measured by pressure tests in order to evaluate the relationship between spherical irregularities and collapse strength. The strength-to-weight ratios of fabricated pressure hulls were significantly higher than that of syntactic foam for deep-sea operations, therefore it is expected that engineering ceramics can be among the promising structural materials for lightening of an underwater vehicle's body.

Effect of Steel Properties on Buckling Pressure of Corroded Pipelines

2017 ◽  
Vol 898 ◽  
pp. 741-748 ◽  
Author(s):  
Meng Li ◽  
Hong Zhang ◽  
Meng Ying Xia ◽  
Kai Wu ◽  
Jing Tian Wu ◽  
...  
Keyword(s):  
Finite Element ◽  
Yield Strength ◽  
Strain Hardening ◽  
Corrosion Damage ◽  
Element Model ◽  
External Pressure ◽  
Strain Hardening Exponent ◽  
The Finite Element Method ◽  
Collapse Pressure ◽  
Steel Properties

Due to the harsh environment for submarine pipelines, corrosion damage of the pipeline steels is inevitable. After the corrosion damage, pipelines are prone to failure and may cause serious consequences. The analysis of the effects of different steel properties on the collapse pressure of pipelines with corrosion defects is of importance for the option of appropriate pipeline and avoiding accidents. Based on the finite element method, the finite element model of the pipeline with defects under external pressure was built. Firstly, the accuracy of the numerical model was validated by comparing with previous experimental results. The effects of yield strength and strain hardening exponent on collapse pressure of pipelines with different sizes of defect were discussed in detail. Results showed that the yield strength and strain hardening exponent have different influences on collapse pressure: the collapse pressure increases with the increasing yield strength, and the collapse pressure decreases with the increasing strain hardening exponent.

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