Technological Residual Stresses Research Articles

ПЕРСПЕКТИВНЫЕ НАПРАВЛЕНИЯ ПОВЫШЕНИЯ ЭФФЕКТИВНОСТИ ШЛИФОВАНИЯ ПОВЕРХНОСТЕЙ ДЕТАЛЕЙ МАШИН

The problem of grinding process increase for machine parts surfaces can be solved by means of abrasive disks design updating, their composition and impregnation technologies. The structures of multiple grinding wheels containing rods in a basic abrasive mass including conducting elements are offered. Such disks allow increasing quality in surfaces machined of parts made of tough hardtomachine steel and alloys on the basis of nonferrous metals on indices of roughness, technological residual stresses and burns. High efficiency show multi-sector abrasive disks of different grain allowing the increase considerably the intensity of material removal at machining parts made of chro-mium-nickel steel and alloys. The effective composi-tions of abrasive masses are developed for tool manufacturing including the introduction in them highstrength ferritic iron, chromium diiodide and wood resin. Polishing tools made of abrasive mass have 1.5 –twice higher durability between stropping operations and ensure the decrease of burn areas quantity on ma-chined surfaces of parts 2-2.5 times. The promising direction of the efficiency increase in parts surface grinding is the impregnation of abrasive disks by an aqueous solution of chromium diiodide which possesses high anticeptic properties and at the iodine emission forms iron iodides with a low constant of friction. As a result of this the temperature drops in the grinding area by more than 30%.

Технологические остаточные напряжения после обработки металлов давлением

The method of calculation of technological residual stresses generated in the process of plastic deformation in the manufacture of hollow axisymmetric metalware (wire, rods, pipes) is offered that takes into account the degree of plastic deformation and strain hardening of the material and allows to determine the level and distribution of residual stresses in the workpiece depending on the type of metal forming, main process parameters, as well as mechanical properties of the processed material. Solutions are obtained analytically. Equations that determine residual stresses contain key working process parameters, mechanical properties of the material and geometrical characteristics of the product. Knowledge of the residual stress level permits to predict metalware behaviour under service loads and to prevent their fracture.

The influence of residual technological stress and service heat loads on the strength of railway wheels

The article deals with the existing approaches to assessing the strength of railway wheels and the problems associated with forecasting actual spots of fatigue crack origination in operation. Solid-rolled railway wheels with a flat cone disk of standard design that have become a frequent practice in the Russian railway system are taken as an example. Calculations of the safety factor of fatigue resistance according to domestic and foreign standards have been carried out. The authors propose a procedure for assessing the wheel fatigue resistance to solve the above problems, taking into account the impact of residual technological stresses caused by heat treatment in the manufacturing process, followed by the repair of the rim, and service heat loads associated with the heating of the rim during braking, when the wheel interacts with blocks. Quantitative assessment of the impact of residual technological stresses and service heat loads on the strength of the wheels is presented. In conclusion the results of testing the computational methods described are presented, wheels of low-stress design with improved performance characteristics developed by the JSC «Vyksa Steel Works» taken as an example.

Theoretical Calculation of Critical Values of Technological Residual Stresses

Theoretical Calculation of Critical Values of Technological Residual Stresses

Methods of the calculation and experimental determination of the local residual stresses under spectrum development of complex loading

The problems of the analysis of residual technological stresses (RS), the knowledge of which is one of the important conditions for the substantiation of strength, service life, and safety of machinery, are investigated. The methods of calculated estimation of the stress occurring during elastoplastic deformation of metals under varying temperature, as well as a modern approach to the experimental estimation of residual stresses, are set out. The experimental method used is based on the processing of large volumes of experimental data from the displacement fields in the area of the probe holes, which are registered by the interference-optical digital methods. An example of the study of residual stresses in a large-diameter pipeline is given, which is made using local induction heating using high-frequency mechanical loading.

Optimal Control of Vitrifying Polymers Cooling Process to Reduce Residual Stresses

This paper’s purpose is analyzing a problem of optimal control of vitrifying polymers cooling process. A solution methodology is suggested targeting at decreasing technological residual stresses, which predetermine major operating characteristics of polymer structures. The criteria function to be minimized is maximum intensity of technological residual stresses under minimum cooling process time. To determine technological residual stresses, a problem of thermoviscoelasticity is solved in finite-elemental formulation. The chosen mathematical model of mechanical behavior of viscoelastic bodies under thermorelaxation transition allows to formulate and to solve the problem of cooling process optimal control. Obtained results show that application of optimal control methods to vitrifying polymers cooling process lead to tenfold decrease of technological residual stresses when compared to an uncontrolled process.

Residual Stress in Plain Carbon Steel Induced by Laser Hardening

Technological residual stresses have great importance in the manufacturing processes and the lifetime of components. The residual stresses formed by quenching can be very diverse because of its multiple sources. Alternative quenching processes such as laser hardening have a great potential for different applications. The direction of heat transfer during laser hardening is the opposite compared to conventional quenching. This further increases the complexity of the developed stress state. The residual stress profile and the microstructure formed by laser hardening treatment are investigated in the present manuscript.

ФОРМИРОВАНИЕ РАСПРЕДЕЛЕНИЯ УПРУГО-ПЛАСТИЧЕСКИХ ДЕФОРМАЦИЙ В СТЕРЖНЯХ В РЕЗУЛЬТАТЕ ДЕЙСТВИЯ ВОЛНОВЫХ ПРОЦЕССОВ

The paper considers the issues of ensuring the uniformity of deformation of elastic shafts and screws under the simultaneous action of the longitudinal loads and heating during thermal-power processing. The uniformity of residual deformations in the longitudinal direction ensures the equalization of the residual technological stresses, and it leads to the minimum buckling in the axial direction due to the stress relaxation. These questions are particularly topical for the lead screws which have strict requirements for the spacing accuracy. The paper presents the results of experimental studies on the influence of main technological modes of thermo-power processing: the degree of deformation, deformation rate and heating temperature on the uniformity of deformation along the length of the shaft, which is expressed by the coefficient of locality, which is defined as the ratio of maximum deformation of one of the sections to the average or minimum deformation of areas. The authors give the comparison of the hardening curves obtained during theoretical modeling of the deformation process and from the results of the full-scale experiment which followed by a conclusion on the unstable, oscillating deformation nature at the stage of plastic flow. Among various theories concerned with the possibility of deformation wave occurrence during parts load, in the elastic task formulation of impact disturbances, the wave theory of elasto-plastic deformations distribution under the static loading was used for explanation of non-uniformity of plastic deformations distribution along the length of the sample. On the basis of Voigt rheological model, phase trajectories for different parameters of the system were obtained, that showed the feasibility of implementation within the system of damped wave processes. Taking it into account, the authors suggested controlling of the process of formation of residual stresses distribution in view of the forming node areas and antinodes of the elasto-plastic deformations.

The influence of residual technological stress and service heat loads on the strength of railway wheels

The article deals with the existing approaches to assessing the strength of railway wheels and the problems associated with forecasting actual spots of fatigue crack origination in operation. Solid-rolled railway wheels with a flat cone disk of standard design that have become a frequent practice in the Russian railway system are taken as an example. Calculations of the safety factor of fatigue resistance according to domestic and foreign standards have been carried out. The authors propose a procedure for assessing the wheel fatigue resistance to solve the above problems, taking into account the impact of residual technological stresses caused by heat treatment in the manufacturing process, followed by the repair of the rim, and service heat loads associated with the heating of the rim during braking, when the wheel interacts with blocks. Quantitative assessment of the impact of residual technological stresses and service heat loads on the strength of the wheels is presented. In conclusion the results of testing the computational methods described are presented, wheels of low-stress design with improved performance characteristics developed by the JSC «Vyksa Steel Works» taken as an example.

Estimation of the admissibility of circular-crack-type defects in the zone of welded field joints of main pipelines

We have considered welded joints of rectilinear parts of underground or overground (in embankment) pipelines with point defects, which are modeled by internal circular surface cracks. We have determined their stressed state induced by the action of internal pressure, temperature drop between the mounting and operation temperatures, and technological residual stresses. On the basis of the two-parameter criterion of the mechanics of brittle–viscous fracture, with the use of failure assessment diagrams, we have calculated the coefficients of safety margin of such a part of the pipeline with a crack in the weld and the admissible defect sizes.

Simulation of defects and stresses in castings

For cast aluminum wheel both the technology of low-pressure permanent mold casting and the bending test were simulated. The shrinkage defects and residual stresses were predicted by computer methods. The total stress fields were examined taking into account the metal structure and the technological features. Non-uniform strength distribution was detected in the cast alloy. It was shown that the technological residual stresses affect the magnitude and distribution of stress concentrators in the part under load.

On the strength of polycrystals of boron nitride dense modifications

An analytical algorithm for the calculation of stresses in polycrystals of boron nitride dense modifications has been described. The relations established between the tensile and compression strength have been based on the Griffith fracture hypothesis for a biaxial stressed state. The effect has been taken into account of technological residual thermal stresses, which are formed in wurtzitic boron nitride (wBN) grains in sintering at the stage of cooling because of the thermal expansion anisotropy, on the strength of wBN.

Assessment of the level of technological residual stresses and their impact on wear resistance of detonation coatings

Assessment of the level of technological residual stresses and their impact on wear resistance of detonation coatings

Composite risers for deep-water offshore technology: Problems and prospects. 1. Metal-composite riser

Prospects for the application of advanced composites in the offshore technology of oil production are considered. The use of composites in vertical pipelines-risers seems to be the most efficient. The operating loads are studied and the attendant problems are formulated. A comparative analysis of the characteristics of metal, composite, and metal-composite deep-water risers is presented. A technique is developed for designing multilayered risers, taking into account the action of internal and external pressures, gravity, and the axial tensile force created by tensioners, as well as the residual technological stresses due to the difference in coefficients of thermal expansion, physical-chemical shrinkage, and force winding. Numerical estimations are given for a two-layered riser with an inner metal layer of steel, titanium, or aluminum alloys and a composite layer of glass- or carbon-fiber plastics formed by circumferential winding. It is shown that the technological stresses substantially affect the characteristics of the riser.

Determination of residual stresses in glass shells by a computational-experimental method

A method is proposed for determining the technological residual stresses in glass shells of revolution based on the solution of inverse problems of shell theory with proper stresses and the use of experimental data obtained by the photoelastic method.

Effect of residual stresses on the strength and endurance of surface-hardened parts

The authors present an evaluation of the most widely used methods of increasing the strength of equipment for the gas and oil industry thermochemical treatment and the application of a strengthening protective coating. In the process of surface hardening of parts, considerable residual technological stresses arise, and when they are added to the stresses induced by external forces, a complex state of stress is produced in the parts, which may considerably affect the strength and endurance of the parts involved. The strength and endurance of surface-hardened drilling pipes, pump bushings, plungers, glazed pump-compressor pipes and casings, etc., depend to a considerable extent on the magnitude and nature of the distribution of the residual stresses. However, in stress analysis and calculation of the wear resistance of these parts, the increased strength of the surface layers alone is taken into account as a rule. The effect of residual stresses on the strength and endurance of products is at present determined mainly experimentally.

Residual technological stresses in the winding of the stator of large electrical machines

Equations were derived for calculating RTS in the gap part and the zone of bending the coils and bars of the stator winding; it was shown that in calculating the RTS in the bending zones, it is necessary to take into account the presence of residual stresses in the copper of the bar. The calculated and experimental results indicate the high concentration of the stresses σX in the bending zones, These regions are most critical from the view-point of possible disruption of the monolithic nature and reduction in the electrical strength of the housing insulation.

Examination of residual technological stresses by holography and speckle interferometry

Examination of residual technological stresses by holography and speckle interferometry

Experimental investigation of the initial stressed and deformed state of three-layer cylindrical shells

In modern technology more and more use is made of three-layer cylindrical shells with load-carrying layers made of high-strength composite materials and with fillers consisting of polymeric foam materials. The initial stressed state in such shells is due to residual technological stresses which can be determined from theory [1-4] or experimentally [1, 4-6]. For the assessment ef the initial stressed state of the filler and of the construction as a whole, experimental data are required on the residual stresses. The complicated theoretical account of all aspects of the interaction between the materials jeined to form the three-layer structures requires an experimental analysis of the changes in the stressed and deformed state during the manufacture of the construction. In the present work, the initial stressed and deformed state of three-layer cylindrical shelis was investigated by studying the kinetics of the technological stresses and deformations on the basis of a division of the components with respect to filler and load-carrying layers. In order to assess the initial stresses and deformations in the elements of the construction, let us discuss the sequence of the manufacturing process of the three-layer shell. In the first stage the inner load-carrying layers are formed and subjected to thermal hardening, which is in essence analogous to the formation of a wound cylindrical article. In this respect the experimental assessr~,,~ of the initial stressed state of the load-carrying layers consists in the determination of the residual stresses by a nondestructive method [1, 7, 8]. Two types of interaction between the load-carrying layers and the mandrel can take place: the contact pressure becomes equal to zero or remains different from zero. The calculations made in [1-3] and the investigations of the kinetics [7-9] of the technolegical stresses and deformations in sufficiently thick-walled articles show that usually the first variant takes place. In the following stage the filler is joined to the inner load-carrying layers and the outer load-carrying layers are wound onto the two-layer structure. The three-layer shell prepared in this way is subjected to thermal treatment. The stress redistributions occurring in this process in the winding elements [8, 9] and the thermal deformation effects in the filler result in a change of the stressed and deformed state of the shell.

Effect of the boride sublayer in silicide coatings on the mechanical properties of molybdenum at high temperatures

1. The boride layer in a siliconized coating on molybdenum has a marked effect on its mechanical properties, increasing the yield stress and strength at, say, 1600°C by approximately 70%. This is accompanied by a significant decrease in plasticity. 2. Strengthening of molybdenum by a boride layer with a high modulus of elasticity is due to the Roscoe effect and to the influence of technological residual stresses. The latter is confirmed by the presence of yield stress and strength maxima at 900°C. Both strengthening mechanisms are confirmed by the dependence of these maxima on the strain rate.