Combinations Of Internal Pressure Research Articles

Spherical Shape Thermoforming of Textile Thermoplastic Composite Tube.

This paper deals with deformation characteristics of textile composite tubes in spherical shape thermoforming process. The composite tubes are made of cowoven braid, which consists of polyamide resin and carbon braid with thin thickness and high fiber volume fraction, and are fabricated by internal pressure bonding method. Spherical shape closed dies of two different sizes are used in the experiment. The specimen is deformed at a temperature that makes the specimen soft enough to be deformed. Several combinations of internal pressure and axial displacement, which are controlled by a personal computer, are applied to the specimen during forming. An expression to predict a required axial displacement for the forming was derived from geometric deformation model of a braid. A spherical shape part being about two times as large as original tube diameter is obtained under suitable forming conditions. Calculated axial displacements agree with experimental results. It is proved that the derived equation is valid to predict required axial displacements for spherical shape forming. Experimental results reveal that this forming process has a potential as one of thermoforming techniques for the composite tubes.

Raman-active phonons in Bi 2Sr 2Ca n−1 Cu nO 2 n+4 d ( n=1,2,3) – phonon assignment and charge redistribution effects

The phonon Raman spectra of Bi 2Sr 2Ca n−1 Cu n O 2 n+4 d ( n=1,2,3), high- T c superconductors have been investigated in a number of single-crystal and polycrystalline samples. From the polarization and doping dependence, and from a comparison with previous reports on other high- T c cuprates, we identify the A 1g and B 1g symmetry modes that are Raman allowed within the ideal body-centered-tetragonal unit cell. On the basis of the assignments proposed here, we discuss the influence of aliovalent substitutions on the phonon modes in Bi 2Sr 2− x La x CuO 6+ d and Bi 2Sr 2Ca 1− y Y y Cu 2O 8+ d . We interpret the observed changes in phonon frequencies and intensities as a combination of internal pressure and charge redistribution effects induced by doping.

The Ethiopian Transition: Democratization or New Authoritarianism?

The early 1990s became the age of instant democracy in Africa in the same way as the mid-1970s were the age of instant socialist transforma- tion. In both periods, a combination of internal pressures, the carrots offered and sticks wielded by outside supporters, and prevailing intel- lectual fashions led a considerable number of African regimes to pro- claim their allegiance to the ideology of the moment. With the benefit of hindsight, it is easy to conclude that those African countries that attempted a sudden transition to a Soviet-inspired social- ist model succeeded in creating only very pale replicas of the original. They put in place the formal trappings of the system, but without the substance. Governments lacked the necessary tools for political and eco- nomic control, and the underlying structural conditions did not lend themselves to the desired transformation. Without the benefit of hindsight, it is difficult to reach equally firm conclusions about the success of instant democratization, but there are reasons to doubt that forced, rapid transformation can be more than a purely formal process, without content. Ethiopia provides an interesting example of a country that attempted instant socialist transformation in the 1970s and 1980s and is now pur- portedly engaged in an ambitious attempt at democratic transformation. The process, which started after the overthrow of the Mengistu regime in May 1991, was expected to culminate during 1995 with the elections for a new parliament.

Influence of winding angle on the strength and deformation of filament-wound composite tubes subjected to uniaxial and biaxial loads

Experimental data are presented to show the effects of winding angle on the strength of 100 mm diameter, 1 mm thick, filament wound E-glass fibre reinforced epoxy resin tubes tested under various combinations of internal pressure and axial tension or compression. Leakage and fracture strength envelopes are presented for ±45°, ±55° and ±75° winding angle tubes subjected to a wide range of different biaxial membrane stress states. Strengths range from 30 to 1250 MPa. Axial compression test results for tubes with wall thicknesses ranging from 1 to 3·6 mm establish the influence of shell buckling. Stress/strain curves up to fracture under three different types of loading show the effects of the winding angle on elastic constants and on nonlinear stress strain behaviour.

Stress analyses of wrinkle bends in pipelines

Wrinkle bends are made by developing local outwards-directed folds at the intrados. The stresses can arise from any combination of internal pressure and change of angle, the latter often arising from thermal effects. Although wrinkle bends are not commonly used in large pipelines nowadays, there are many in existing pipelines built years ago. The paper shows that the stresses are mainly due to local bending of the pipe wall and have peak values which can be quite large especially on the inside surface of the highest point of the wrinkle. Graphs which enable these stresses to be evaluated separately for internal pressure and for longitudinal displacement (or thermal loading) are provided.

Multiaxial characterization of T800/3900-2 carbon/epoxy composites

The individual plies of fiber composites are typically used under conditions of multiaxial stress. However, relatively little is known about the response of fiber composites to multiaxial stress, and this is particularly true with respect to strength properties. This paper presents the results of an investigation into the multiaxial strength and stiffness properties of Toray T800/3900-2, which is a high-strain-capability carbon fiber with a high-toughness epoxy-matrix system. Tests were carried out on tubular specimens loaded under combinations of internal pressure, axial tension or compression, and torsion. The tests involved both unidirectional lamina specimens, to determine matrix-dominated properties, and laminate specimens involving three different types of layup. The laminate test results showed that ultimate failure could be satisfactorily correlated by using a maximum-fiber-direction-strain failure criterion.

A class of composite loads for an inelastic material

In solid mechanics a considerable role is played by flow, which in a certain sense is the simplest form. In hydrodynamics this relates to Couette flow between parallel plates and coaxial cylinders [1], in solid mechanics it relates to deformation of thin-walled tubular specimens [2], and in the mechanics of loose materials it relates to uniform shear of the material [3]. Construction of sufficiently general phenomenological models assumes an experimental study of different loading paths, including composite loading paths when the stress tensor axes are turned relative to the volume of the material. Composite loading of metals, rocks, and other solids may be realized by a combination of internal pressure, torsion, and tension for tubular specimens. However, for a broad class of materials this classic procedure is either markedly complicated (e.g., for soils [4]), or it is generally inapplicable. It is of interest to find a class of composite loads which on one hand might relate to the simplest, and on the other might be used in order to test loose, viscoelastoplastic, and other similar materials.

Fracture stresses for ± 75 degree filament wound grp tubes under biaxial loads

Fifty, 100 mm diameter ± 75 degree filament wound E glass fibre/epoxy resin tubes have been tested to destruction under various combinations of internal pressure and axial tension or compression. The test equipment and procedures are described. The method of reinforcing and gripping the ends of the specimens avoided end failures. The effects of possible stress concentration at the ends are considered. Experimental fracture stresses are presented and compared with theoretical results for a variety of biaxial loading conditions.

Assessing instability of thin-walled tubes under biaxial stresses in the plastic range

It is becoming increasingly necessary to obtain data on the biaxial-stress behavior of many materials. One of the most commonly employed methods of obtaining this information, over a wide range of stress ratios, consists of subjecting thin-walled tubes to various combinations of internal pressure and independent axial load. Some of the problems associated with this method of testing are discussed, together with a description of how they may be overcome in order to apply pressures of up to 20,000 psi and axial loads of 35,000 lb. A new method is presented for producing conditions of constant-mean-stress ratio which takes into account the changing dimensions of the specimens.

Effect of Polyaxial Stress States on Failure Strength of Alumina Ceramics

The effect of polyaxial stress fields on the brittle fracture strength of polycrystalline alumina was investigated through the use of thin-walled cylinders. Combinations of internal pressure, external pressure, and axial loads produced stress states of tension-compression, tension-tension, and compression-compression. The failure envelope was generated for these stress states. The results indicated that biaxial tensile stresses reduced the strength of the material; however, the tensile strength increased at least 50% when a compressive stress existed normal to the tensile direction. Compression strengths as high as 640,000 psi were measured for a biaxial compressive stress state.

The Plastic Flow of Thick-Walled Tubes with Large Strains

The theory for the plastic flow of thick-walled tubes is discussed for a material having an arbitrary true stress-strain curve, loaded by any combination of internal pressure, external pressure, and end load, where the strains may become large necessitating the use of finite true strain definitions. Comparisons are made of the finite strain theory, the infinitesimal strain theory, and experimental results for the special case of a closed end thick-walled tube of aluminum. The comparison shows that the infinitesimal strain theory is considerably in error even at moderate strain values. The finite strain theory appears to be satisfactory even for strains somewhat beyond the value for the local bulging of thick-walled tubes.

Partially plastic thick-walled tubes

A theory is presented for the partial plastic yielding of thick-walled cylindrical tubes acted upon by any combination of internal pressure, external pressure and end load when the material follows an arbitrary stress-strain law. The solution combines (a) the distortion energy theory of plastic flow and (b) the effects of elastic compressibility of the plastic material. Numerical values for stresses and strains are given for certain special cases of internal pressure in thick-walled open-ended tubes for an idealized stress-strain law, and the results are compared with earlier approximate theories.