МЕТОДОЛОГИЧЕСКИЕ ОСНОВЫ МАТЕРИАЛОВЕДЧЕСКОЙ ОЦЕНКИ КАЧЕСТВА СМАЗОЧНЫХ СРЕД ДЛЯ НАГРУЖЕННЫХ СОПРЯЖЕНИЙ МАШИН И МЕХАНИЗМОВ. Сообщение 1. Влияние среды на напряженно-деформированное состояние и структурные изменения в зоне контактной деформации металлов при трении

The significance of residual stresses in relation to the integrity of LWR pressure vessels

In order to control the residual stress and distortion of welded joints, various welding methods such as symmetry, .step back, skip method etc. are used in actual works. In this report, we compared each other the residual stress distributions of the joints welded by these methods.In most case the joints of actual structure are welded under constrained state, and so the determination of welding sequence is one of the most important problems in actual works. In this repot, we used the constrained specimen as shown in Fig. 1, and discussed the effect of welding sequence on the residual, locked-in and weld stresses. For the sake of convenience, we call these experiments "Test I" and "Test II" respectively.Material used is SS 41 steel plate. The specimens in "test I" are 500×200×6 mm bead-welded specimens, 500×100×6mm and 500×100×19mm butt-welded specimens, which, are welded along the 500 mm edge. The welding methods and conditions are shown in Table 1. In "test II", we used the three welding sequences shown in Fig. 2.The residual stresses were measured by SR-4 strain meter. In "Test II" the locked-in stresses were at first measured by cutting the chain line in Fig. 1 and next the residual stresses were measured by usual trepanning method.The results of the tests are shown in Figs. 3, 4, 5, 7 and 8. Fig. 6 shows schematic diagram of the residual stress distribution of bead-welded plate. This diagram was obtained by simple stress analysis. We compared this diagram with the experimental results, and discussed the effect of welding methods and welding sequences.The distributions of residual stress in test I agree in most case with the schematic diagram, Fig .6, but the result of specimen A-4 (skip method) is a little different. In this specimen, transverse stress increases in spite of the decrease of longitudinal stress, and the peaks of residual stress are produced at the last bead. In test II, stress distributions are a little different from the schematic diagram. This difference is due to the disturbance of external constraint and the cross point of welded joint.At last we discussed which method and sequence is favorable from the view point of residual stress distribution. We adopted maximum stress and triaxial ratio as the criterion of comparison, where triaxial ratio is defined by |σ1+σ2+σ3|/3|σmax|. (σ1, σ2, and σ3 are principal stresses and σmax is maximum principal stress.) The maximum stress values and triaxial ratios are shown in Table 2 and 3. From these results we concluded as follows : (1) In the case that the thin plate is welded by one pass, skip method gives comparably small residual stress, but for thick plate welded by multiple pass, cascade block method is most favorable from the view point of residual stress distribution. (2) In constrained specimen, it is favoured to weld at first the shorter joint (for example vn and 'p'Y in specimen "D") before welding longer joint (for example gg' in specimen "D").

Finite element analysis of the thermal residual stresses of SiC particle reinforced aluminum composite

The finite element analysis method was applied to simulate the gradient field heat treatment process of a cylinder welding component of 30Si2MnCrMoV steel by software ANSYS. In the heat treatment process，the distribution of temperature field, the variation curve of residual stress with time，the distribution of residual stress along the axial direction of cylinder, and the axial and radial deformation of the specimen were calculated and the influences of partial heating area on the distribution of temperature and residual stress were analyzed. The calculating results show that the temperature in the weld metal zone and heat affected zone of welding specimens may exceed the phase transformation points during the gradient heat temperature. The residual stress and the radial deformation in the weld metal zone were greater than those in the matrix zone. The final deformation of specimen was along the axial direction. With the increase of partial heating area, the phase transformation area was increased and the residual stress was reduced effectively.

To investigate the effect of power density on the residual stress distribution on the surface of 17-7 PH stainless steel welded joints during laser shock process, we utilized ABAQUS finite element software for analyzing its distribution under different laser shock power densities. The material was tested for residual stress using an X-ray stress diffractometer to verify the accuracy of the simulation results and lay the foundation for finding the optimal process parameters. The simulation results show that when the laser power density is 2.79 GW/cm2, the maximum residual compressive stress value on the surface of the sample after laser shock peening is −37.2 MPa; When the laser power density is 2.79 GW/cm2, the maximum residual compressive stress value on the surface of the sample is −94.1 MPa; When the power density reaches 5.17 GW/cm2, the maximum residual stress value on the surface of the laser shock peening sample is −144.8 MPa, and residual stress cavity is formed. The experimental results show that when the laser power density is 2.79 GW/cm2, the maximum residual compressive stress on the surface of the sample is −37.3 MPa; When the power density is 3.98 GW/cm2, the uniformity of compressive stress distribution on the surface of the sample is optimal, with a maximum residual compressive stress value of −99.0 MPa; When the power density is 5.17 GW/cm2, the maximum residual compressive stress value is −146.1 MPa, and residual stress cavity is formed on the material surface. The simulation results are close to the experimental results, and the model error ranges from 0.2% to 4.9%. The simulation results are accurate and reliable.

Liquid nitrogen(LN2) cryogenic machining is a green, sustainable, and high-performance machining technology. LN2 cryogenic machining of TC4 can significantly strengthen the local cooling environment of cutting, accelerate the heat dissipation, thus effectively reduce the cutting temperature, and suppress the generation of thermal stress, reduce the residual tensile stress on the workpiece surface. In this paper, a finite element model(FEM) of numerical prediction is established to analyze the effect of LN2 cryogenic machining on residual stress distribution. Firstly, mechanism analysis of surface residual stress is carried out to explore the source of residual stress during TC4 cryogenic turning. Next, to observe residual stress distribution clearly, the cutting zone separation model is designed, and then, the material model is built to reflect the change of material properties. Then, a FEM of the numerical prediction made up of explicit dynamic solution module and standard static solution module is established to simulate residual stress distribution; after that, residual stress can be ultimately acquired by linear superposing the above two module simulation results. Based on FEM proposed in this paper, the effect of LN2 cryogenic machining on surface residual stress distribution of TC4 is analyzed, and it is indicated that LN2 cryogenic machining can reduce the residual tensile stress effectively. Finally, the experiment is carried out, and the results show that the general trend of the prediction model is the same as that of the experimental results, which greatly verify the availability of the prediction model. Research provides some reference for the numerical prediction and suppression of residual stress in the future.

316L stainless steel pipes are widely used in the storage and transportation of low-temperature media due to their excellent low-temperature mechanical properties and corrosion resistance. However, due to their low thermal conductivity and large coefficient of linear expansion, they often lead to significant welding residual tensile stress and thermal cracks in the weld seam. This also poses many challenges for their secure and reliable applications. In order to effectively control the crack defects caused by stress concentration near the heat-affected zone of the weld, this paper establishes a thermal elastoplastic three-dimensional finite element (FE) model, constructs a welding heat source, and simulates and studies the influence of process parameters on the residual stress around the pipeline circumference and axial direction in the heat-affected zone. Comparison and verification were conducted using simulation and experimental methods, respectively, proving the rationality of the finite element model establishment. The axial and circumferential residual stress distribution obtained by the simulation method did not have an average deviation of more than 30 MPa from the numerical values obtained by the experimental method. This study also considers the effects of welding energy, welding speed, and welding start position on the pipe's circumferential and axial residual stress laws. The results indicate that changes in welding energy and welding speed have almost no effect on the longitudinal residual stress but have a more significant effect on the transverse residual stress. The maximum transverse residual stress is reached at a welding energy of 1007.4~859.3 J/mm and a welding speed of 6.6 mm/s. Various interlayer arc-striking deflection angles can impact the cyclic phase angle of the transverse residual stress distribution in the seam center, but they do not alter its cyclic pattern. They do influence the amplitude and distribution of the longitudinal residual stress along the circumference. The residual stress distribution on the surface of the pipe fitting is homogenized and improved at 120°.

The investigations were made on steel type 20ΗΝM, used for carburizing.The specimens were carburized at different time periods as to obtain differentiated thicknesses of diffusion layers.The carburized layers of thickness ΗV550 from 0.6 to 1.3 mm were pneumatically shot peened with steel shot 0.8 mm (S280) and the time of exposition of the shot peened surface varied.The value and distribution of residual stresses at carburized layers as well as carburized and shot peened ones were determined.The measurements were done by destructive method.There were recorded the strains of the flat sample after the release of residual stresses in result of removing, by etching, a thin layer of the material.The fatigue characteristics were determined, for the preset technological parameters, at four-point bending.It was proved that the increase in fatigue strength was the result of the changes of value and distribution of compressive residual stresses caused by structural changes which appear at carburized layer after shot peening.By means of Mossbauer spectroscopy, the changes of retained austenite at carburized samples, which appear as the result of surface plastic strain caused by shot peening, were determined.The results of the investigation should be used in technology of hardening of highly loaded gears.

Numerical predictions and experimental measurements of residual stresses in fatigue crack growth specimens

One of the primary challenges associated with the laser powder bed fusion process is the presence of residual stress. These residual stresses arise from the significant thermal gradients induced by the rapid heating and cooling of the material, which are inherent to the laser powder bed fusion process. Such stresses can contribute to crack formation, distortion, and, ultimately, failure of the component. Consequently, effective control of residual stress is of paramount importance. In this study, an analytical approach was employed to establish the relationship between the distribution of residual stresses within samples exhibiting two variable cross-sectional geometries. Utilizing the principles of force and moment equilibrium, the distribution of residual stresses in each layer of the sample was determined. To validate the analytical method, experimental measurements of residual stresses in both the surface layer and the interlayer region of Inconel 625 samples were conducted. Additionally, the impact of hatch distance on the residual stress within the experimental samples was examined. Residual stress measurements were performed using a non-destructive X-ray diffraction technique. The results from the experimental analysis indicate that an increase in hatch distance correlates with a reduction in residual stress. Furthermore, a comparison between the residual stress at the center of the surface layer and that at the interface of the variable cross-sectional sample reveals that the residual stress at the interface is approximately halved.

In order to obtain good estimates of stress intensity factors in a structural integrity assessment, the accuracy with which a residual stress distribution is represented should be commensurate with the importance of localised peaks in residual stress, in particular where such peaks lie within the region under assessment. This paper describes work undertaken to investigate the importance of accurately representing residual stress distributions in structural integrity assessments. This has been carried out by comparing regular polynomial representations of residual stress distributions, combined with available weight function stress intensity factor solutions (as provided in the R6 procedures) with alternative polynomial representations of residual stress distributions, which provide a more accurate fit in the region of the crack. Such improvements in representation of residual stress profiles provide an indication as to how stress intensity factor solutions could, in future, be modified in order to result in improved accuracy of calculated stress intensity factors. Representation by partitioning residual stress profiles into membrane, bending and self-balancing components, in terms of providing a more straight-forward route for curve-fitting of residual stress profiles is considered. The investigation considers several transverse, through-thickness residual stress distributions. Stress intensity factors are calculated for a variety of crack sizes. Representation of the residual stress profiles in the stress intensity factor solutions are compared, as are the results of the stress intensity factor calculations. The conclusions arising provide guidance as to how current methods of curve fitting a residual stress distribution may be improved in cases where current methods may not be accurate. Advice is also provided as to the relative merits of representing residual stress distributions as a set of partitioned components or as a single distribution.

AF1410 steel is a kind of high alloy ultrahigh strength steel with perfect hardness, strength and fracture toughness after secondary hardening heat treatment. The distribution of residual stresses affects the fatigue life and stress corrosion resistance of the components in service. Little investigation about the residual stresses on AF1410 steel had been studied previously. The distribution of surface residual stresses on the components should be controlled by the machining process. In this study, two AF1410 workpieces machined by the orthogonal end-milling experiment of AF1410 were performed. The axial depth of cut, cutting speed, feed rate per tooth and radial depth of cut were involved in to the experimental factors. The residual stresses were measured by X-ray diffraction method. The influence of milling factors on distribution of surface residual stresses was studied with range analysis method. The influence sequence of the factors on surface residual stresses were obtained and the optimum value of cutting parameters were selected.

Utilization of WC-10Co-4Cr coating, sprayed by High-Velocity Oxygen Fuel, has significantly expanded due to its high corrosion and wear resistance. In this study, the in-plane residual stresses in the coating were determined experimentally with the x-ray diffraction technique, using the $${\sin}^{2}\psi$$ method and compared to finite element analysis (FEA). The chemical layer removal process was used to determine the residual stress experimentally, through the thickness of the coating. In the FEA, the effect of impingement of a WC-10Co-4Cr particle on the substrate was first studied and the results of impingement analysis were used as input data in a thermomechanical model of the coating process. Experimental results, in agreement with simulation studies, showed that the in-plane surface residual stresses in the WC-10Co-4Cr coating were compressive. The magnitude of this compressive stress increased with depth, relative to the free surface of the coating. The largest compressive residual stress was measured at the coating–substrate interface. Simulation results predicted that the stress distribution through the coating was uniform, except at the edges of the sample, where tensile stress concentrations existed at the coating–substrate interface. This region is thus prone to cracks and delamination of the coating.

In recent years so much attention has been called to the problem of creep or creep rupture in pressure vessels and tubes that operate at high temperature, and numerous theoretical and experimental works on this problem have hitherto been reported. There are, however, several open questions that must be discussed from the standpoint of multiaxial creep behaviors.The authors have taken interest in this subject and have been carrying out the creep tests of thick-walled cylinders under internal pressure at high temperature. The tests have been made with 0.19% carbon steel at the temperature of 450°C. The tubular specimens had a 400mm cylindrical gauge length, with the outside diameter about 50.45mm and the ratio 2 of outside to inside diameter (OD/ID). The specimens of uniaxial creep tests were cut from the same tubes. The internal pressure was supplied by the hand-operated water-pump and was maintained within ±1% by the pressure controller. The circumferential elongation on the outside diameter of the tubular specimen was measured by dial gauges and mirror-telescope instruments.The results of the tests revealed that the circumferential strain on the outside diameter versus the time relations for the tubular specimens were similar as the strain versus the time relations for the uniaxial tension. The axial creep for the tubular specimens was negligible.In addition to this, this report deals with the results of the measurement of residual stress distributions in the thick-walled cylinders after the creep tests. The measurement was carried out by the well-known Sachs' method. The X-ray method was also used for the residual stress determinations on the outer surface of the cylinder, and a fairly good agreement was obtained between the stress values measured by the two methods.The results obtained were as follows: No residual stress in the cylinder before the creep tests can be measured except near the outer and inner surfaces. The residual stress distributions after the creep tests under 1000kg/cm2 for 1 hour are similar as those under 1200kg/cm2 for 104 hours; that is, the circumferential and axial residual stresses change monotonously from compression on the inner surface to the tension on the outer surface, and the radial residual stress, which is smaller than the others, is compressive in the wall. The stress distributions in creep conditions determined by these measured residual stresses correspond to the steadystate stress distributions. It was also found that the circumferential and axial residual stresses measured by means of X-rays remained constant on the surface of the cylinders after the creep tests under 1000kg/cm2 for 1, 10 and 100 hours respectively.From these results it is found that, as far as the creep of the cylinders at 450°C under 1000kg/cm2 is concerned, the stress distributions change from the initial elastic state to a steady state in a short time. It is the authors' belief that the time required for the stress distributions almost to reach the steady state will be relatively short in the case of creep at high temperature and high stress. However, further discussions on a transient stage will be necessary from the point of view of multiaxial creep theory.

Solutions to problems of pure elastoplastic torsion in surface-plasticized and surface-hardened rods are given. The distribution of residual tangential stresses along the rod radius is shown to have an oscillating and sign-alternating character in both cases. In surface-plasticized rods, in contrast to surface-hardened rods, the residual stresses in the external layer always have the opposite sign with respect to the active loading stresses produced by the outer torsional moment. Conclusions have been drawn about the character of the defect structure changes as well as about the conditions of sample fracture under cyclic torsional tests during the action of alternating outer force moments.