ИССЛЕДОВАНИЕ ДЕФОРМАЦИИ ПОЛЗУЧЕСТИ ПАРОПРОВОДОВ ОСТРОГО ПАРА ИЗ СТАЛИ 12Х1МФ

Subsurface explosions seriously threaten the safety and reliability of buried oil and gas pipeline. In order to investigate the mechanical responses of buried steel pipeline under subsurface explosion load, a numerical model of pipeline–soil coupling under explosion load was developed. Stress, displacement, plastic deformation, and local buckling of the buried pipeline were investigated. The effects of trinitrotoluene (TNT) magnitude, pipeline diameter-thickness ratio, pipeline's buried depth, explosive depth, and explosive offset on the mechanical response of pipeline were studied. The results show that the response time of buried pipeline is very short under the explosion load. There is a dent appearing on the pipeline section toward the exploding location. Cross-sectional area of the pipeline decreases along the time during the explosion, but it gradually increases for the elastic recovery. Pipeline's deformation and total energy increase gradually with the increasing of trinitrotoluene magnitude or diameter-thickness ratio, but they decrease with the increasing of the buried depth or explosive offset. With the explosive depth increases, the pipeline's plastic deformation first increases and then decreases. The pipeline's energy curve can be used to determine the buckling state under explosion load. The empirical formulas of the maximum strain and dent rate for buried pipelines have been obtained and can be used for the pipeline safety assessment.

Nowadays the method of the longitudinal critical refraction wave (LCR wave) is an effective method to nondestructively measure the on-line stress in the huge steel structures. The present study and research of the method of LCR wave are mainly focused on measuring the residual stress in the steel structures, in contrast to the few research findings related to the on-line stress measurement in steel structures (including the elastic and plastic deformation). Based on the Acoustoelastic effect, the LCR wave stress measurement system is built to measure the change of time of LCR wave propagating, stress coefficient and the energy of LCR wave in A36 steel test specimens from the elastic deformation to the plastic deformation. The conclusion is: At the free-stress condition, the flight time of LCR wave and stress coefficient show an obvious change between the elastically deformed test stage and plastically deformed stage. The change of flight time and the intensity attenuation of LCR wave show a turning point, when the specimen undergoes the process from elastic deformation to plastic deformation. And the extent of plastic deformation in the steel structure can be evaluated by the extent of intensity attenuation of LCR wave. The experimental method will be showed in this paper for measuring the extent of plastic deformation in the steel structures in service on construction scene using the LCR wave method.

14 - Development of last-stage long blades for steam turbines

Plastic versus elastic deformation effects on magnetic Barkhausen noise in steel

A dynamic research of marine steam turbine propulsion is very important problem in ship construction and ship exploitation. The creating model presented in this paper is using to research the dynamics of marine steam turbine propulsion. The creating model is based on the marine steam turbine power plant MST-23, one of the most modern marine steam turbine power plant. The results of the research using this model are characteristics of the related changes on the time of the most important parameters of marine steam turbine propulsion plant in the transient states and it's very important for analyzing marine steam turbine propulsion plant in the transient states.

Currently, the standard approach to building a geomechanical model for analyzing wellbore stability involves taking into account only elastic deformations. This approach has shown its inconsistency in the design and drilling of wells passing through rocks with pronounced plastic properties. Such rocks are characterized by the fact that when the loads acting on them change, they demonstrate not only elastic, but also plastic (irreversible) deformations. Plastic deformations have an additional impact on the distribution of stresses in the rock of the near-wellbore zone on a qualitative and quantitative level. Since plastic deformations are not taken into account in the standard approach, in this case the results of the wellbore stability analysis are based on incorrectly calculated stresses acting in the rock. As a result, it can lead to misinterpretation of the model for analysis, suboptimal choice of trajectory, incorrect calculation of safe mud window and an incorrectly selected set of measures to reduce the risks of instability. The aim of this work is to demonstrate the advantages of the developed 3D elasto-plastic program for calculating the wellbore stability in comparison with the standard elastic method used in petroleum geomechanics. The central core of the work is the process of initialization of the elasto-plastic model according to the data of core tests and the subsequent validation of experimental and numerical loading curves. The developed 3D program is based on a modified Drucker-Prager model and implemented in a finite element formulation. 3D geomechanical model of wellbore stability allows describing deformation processes in the near-wellbore zone and includes the developed failure criteria. The paper shows a special approach to the determination of the mud window based on well logging data and core tests by taking into account the plastic behavior of rocks. An important result of this study is the determination of the possibility of expanding the mud window when taking into account the plastic criterion of rock failure.

We demonstrate that the high temperature polymorphic tantalum phase transition from the tetragonal beta phase to the cubic alpha phase causes a large decrease in the resistance of thin films and a complete stress relaxation in films that were intrinsically compressively stressed. 100 nm beta tantalum thin films with intrinsic stresses of 2.0×1010 dynes/cm2 (tensile) to −2.3×1010 dynes/cm2 (compressive) were deposited onto thermally oxidized (100) silicon wafers by evaporation or dc magnetron sputtering with argon. In situ stress and resistance at temperature were measured at 10 °C/min up to 850 °C in purified helium. Upon heating, the main stress mechanisms were elastic deformation at low temperature, plastic deformation at moderate temperatures and stress relief because of the beta-to-alpha phase transition at high temperatures. The temperature ranges over which the elastic and plastic deformation and the beta-to-alpha phase transition occurred varied with deposition pressure and substrate biasing. Incomplete compressive stress relaxation at high temperatures was observed if the film was initially deposited in the alpha phase or if the beta phase did not completely transform into alpha by 800 °C due to substrate biasing during the deposition. We conclude that the main stress relief mechanism for tantalum films with intrinsic compressive stresses to completely relax their stress is the beta-to-alpha phase transition, while for intrinsically tensile films, this transformation has a much smaller effect on the stress.

A rotating hollow cylinder with fixed ends is considered, the inner surface of which is free of stresses, and the outer one is fixed from radial movements. It is assumed that the cylinder is made of an ideal isotropic elastoplastic material, and the deformations in it are small and represent the sum of elastic and plastic deformations. Stresses are associated with elastic deformations by Hooke's law. Plastic deformations are determined using the Tresca - Saint-Venant condition and the plastic flow rule associated with it. The cylinder rotation speed first monotonically increases to a maximum value, and then decreases to zero. By using the elastic solution, the dependence is found for the critical rotation speed at which the plastic flow begins. It is established that, depending on the thickness of the cylinder and the Poisson's ratio, plastic flow can begin, either on the inner or on the outer surface of the cylinder. In addition, 3 plastic regions appear in the cylinder at the loading stage, and 4 plastic regions appear at the unloading stage. These regions correspond to two faces and two edges of the Treska prism. For each plastic region, an exact analytical solution of the determining system of equations is found. The system of conditions at the boundaries between the regions providing continuity of the obtained solutions throughout the cylinder is given. Two cases are considered, i.e. the case with a plastic flow which starts first on the inner, and then on the outer surface of the cylinder. Analytical expressions are obtained for rotational speeds at which new regions appear. The relationship between the nucleation rates of the secondary and primary plastic flow is established. The value of the maximum rotation speed sufficient for a complete transition of the cylinder to the state of the secondary plastic flow was also found. It has been revealed that the adding of a rigid casing can significantly increase the resource of an exploited part.

Insight into the localized strain effect on micro-galvanic corrosion behavior in AA7075-T6 aluminum alloy

Tensile properties of GH4169 superalloy for smooth and notch specimens determined by tests and simulation

Mechanoluminescence induced by elastic and plastic deformation of coloured alkali halide crystals at fixed strain rates

В настоящей работе дилатометрически изучены упруго-пластические свойства сферических зерен промышленных слабокислотных и сильнокислотных ионитов в опытах с постоянным одноосным сжатием и последующей разгрузкой при комнатной температуре в зависимости от ионной формы и концентрации раствора электролита. Показано, что ионная форма полиакрилата и полиметакрилата, сшитых, соответственно, диметакрилатом триэтиленгликоля и дивинилбензолом, и концентрация внешнего раствора влияют на их упруго-пластические свойства. В разбавленных растворах хлорида натрия и хлорида кальция гели проявляют упругие свойства с близкими относительными амплитудами деформирования. Амплитуда деформирования зерна полиметакрилата, сшитого дивинилбензолом, в Ni-форме в разбавленном растворе хлорида никеля оказалась значительно ниже, чем у Са-формы, со значительным вкладом пластической деформации. С увеличением концентрации внешнего раствора хлоридов кальция и никеля под действием механической нагрузки на зерно полиметакрилата, сшитого дивинилбензолом, уменьшалась общая деформация гранулы, а также величина упругой деформации, а остаточные (пластические) деформации увеличивались. В концентрированных растворах CaCl2 и NiCl2 такой ионит становился неупругим жестким материалом, для которого даже при повышенных механических нагрузках величина упругих деформаций сжатия очень невелика. Для набухшего в воде сильнокислотного полистирольного катионита с привитыми сульфогруппами, сшитого дивинилбензолом, в К-форме также характерны упругие деформации, т.е. полимер находится в высокоэластическом состоянии. Однако полистирольная матрица более жесткая по сравнению с полиакриловыми и полиметакриловыми катионитами в форме иона щелочного металла, поэтому амплитуда деформирования существенно меньше. Для такого катионита в Са- и Ni- формах даже в концентрированных растворах преобладающими являются упругие деформации.

The bending behavior of the hydraulic pipeline on the roller of the logging winch will cause a certain plastic deformation of the hydraulic pipeline, which has a certain influence on its performance. In view of the above problems, this paper uses finite element analysis software to analyze the plastic deformation law of hydraulic pipelines under different bending radii. It can be found from the analysis results that during the bending process, the plastic deformation of the metal continuous capillary gradually increases with the neutral layer outward. In the range of the bending radius from 75 mm to 150 mm, with the increase of the bending radius, the equivalent plastic deformation decreases from 3.5×10-2 to 1.46×10-2. The changing trend of life also tends to be gentle with the increase of the bending radius, and the number of cycles increases from 25000 to 398107. The analysis of the plastic deformation law and the life of hydraulic pipelines provides a reference for designing winch drums.

The airtightness of cement sheath under alternating loading and unloading was studied using self-developed experiment facilities, and the mechanism of airtightness failure of cement sheath under alternating loading and unloading was understood based on the experimental results. Under the action of lower alternating pressure inside the casing, the time for the cement sheath to fail can be long; the action of high alternating pressure, on the other hand, will soon break down the airtightness of the cement sheath. This indicates that low pressure inside the casing string imposes low force on cement sheath which still retains its elasticity, and elastic deformation takes place in the cement sheath under alternating loading and unloading. Under the action of high stresses, on the other hand, the intrinsic micro fractures and deficiencies inside the cement sheath begin to connect with each other, and both elastic deformation and plastic deformation take place inside the cement sheath. As the alternating goes on, the plastic deformation becomes accumulated, to the extent that the plastic deformation does not vanish after unloading. Differences in the deformations of casing string and cement sheath at the interface result in a tensile stress, which, when exceeding the cementation strength at the interface, will cause the airtightness of the cement sheath to fail. This is the so-called low cycle fatigue failure of the airtightness of cement sheath under the action of alternating loading and unloading. Higher internal pressure in the casing string results in higher induced stress inside the cement sheath, larger plastic deformation, higher residual strain and tensile stress at the interface after unloading, and, the less of the number of cycles required to cause the airtightness of the cement sheath to fail.

The mechanical work spent on the irreversible deformation of solids is always at least partly dissipated. Therefore, independent of the sign of the heat effect resulting from the elastic deformation, plastic deformation is always accompanied by an exothermic effect. A schematic diagram of thermo-mechanical behavior of an ordinary solid and a solid polymer is shown in Fig. 7.1. After a small amount of initial cooling, resulting from elastic deformation, evolution of heat accompanying the beginning of plastic deformation occurs. The appearence of plastic deformation is accompanied by heat evolution independent of whether it is localized (necking) or distributed along the sample uniformly. If the plastic deformation is accompanied with a neck formation, which is typical of the cold drawing of the majority of glassy and crystalline polymers well below glass transition or melting point, then the heat generated locally may lead to a considerable local temperature rise. This temperature rise may strongly influence the cold drawing of the sample. At low drawing rates the neck propagates uniformly along the sample. Under certain conditions, however, especially at a high rate of extension for some polymers, instabilities of neck propagation can be observed (self-oscillation phenomenon), which is also closely related with the local thermal effects.