Redistribution Of Residual Stresses Research Articles

Efficiency of using vibration treatment of welded stainless steel structures at the welding stages and after its completion

Vibration treatment of welded structures is a tool for relaxation of residual welding stresses, used to stabilize the dimensions over time. The use of this advanced technology in different periods of production has its own characteristics. The traditional performance of vibration action after welding is carried out at resonant or near-resonant frequencies; the result of this action can be estimated by the change in the amplitude-frequency characteristic that occurs due to deformations during relaxation of residual stresses. Another method involves combining welding with vibration, performed at frequencies that ensure the formation of high-quality penetration, the efficiency of this processing is determined, among other things, by reducing residual stresses; in addition, the values of residual deformations are reduced, the shape of the penetration is optimized. The problem of choosing the optimal period of exposure to welded stainless steel structures manufactured using argon arc welding is reduced to comparing the efficiency according to various criteria: redistribution of residual stresses, influence on residual deformations, suitability for control, change in mechanical properties.

A meta-reinforcement learning method by incorporating simulation and real data for machining deformation control of finishing process

Finishing determines the final dimension and geometric accuracy of parts, and the finishing process directly affects the stiffness and residual stress redistribution of the workpiece, so the optimisation of the finishing process plays a very important role in deformation control. At present, existing data-driven methods for deformation control need a large amount of labelled training data, which is always a challenge in the manufacturing area, especially for machining deformation. To address the above issues, this paper presents a meta-reinforcement learning model incorporated by simulation and real data, which is trained in a simulation environment with a piecewise sampling strategy for data collection, and can be updated in a real machining environment through a very small number of real monitoring data. The finishing process optimisation for deformation control can be realised using the proposed approach. Finally, the effectiveness of the proposed method is verified both in simulation environment and actual machining, and better results are obtained compared with other existing methods.

Precise machining based on Ritz non-uniform allowances for titanium blade fabricated by selective laser melting

Selective laser melting (SLM) is an increasingly concerned trend in Ti-6Al-4V blade manufacturing, while the SLMed Ti-6Al-4V blade cannot be used directly because of poor surface integrity and high residual stresses. Precise machining after SLM is a feasible solution but also a challenge. The low rigidity of the blade will lead to deformation when machining. The deformation can lead to surface error and may make defect parts. Two-step machining processes to address the problems were proposed in this paper. First, a non-uniform allowances distribution was allocated and optimized in semi-finishing based on Ritz solution to elastic deformation. The blade was simplified as a cantilever thin plate with various thicknesses, and the thicknesses of finishing allowances were designed and optimized on the premise of ensuring the thin-wall stiffness of the blade, so as to realize the design of Ritz non-uniform allowances. Then, finishing machining was conducted to achieve precise parts. A blade deformation model was established to evaluate part distortions with cutting force moving and changing. Finite element analysis (FEA) and experimental validation in ball-end milling of a blade were conducted. FEA results and experimental results showed dimensional errors have been reduced up to 50%. Further surface tests demonstrated that the mean surface roughness reduced from 7.88 to 0.815 μm. And the residual surface stresses of the SLM samples changed after semi-finishing machining due to the residual stresses relaxation and redistribution. The results demonstrated that the proposed method enhanced the surface quality of the blade fabricated by SLM.

Overview of effect of residual stress, elastic follow-up & stress redistribution using whole structure approach

Structural integrity assessments of components require accurate predication of failure of components. One of the major challenges while doing structural integrity assessment is to understand whether the presence of residual stresses in the component acts a major part in the failure of complete structure or not. Residual stresses may arise during manufacturing, fabrication or can also get induced during service and with addition of applied load promote failure at much below safe design loads. In general, residual stresses are considered as secondary stresses but in cases where they doesn’t self-equilibrate in the structure, leads to plastic collapse, they should be treated as primary stresses. Whether residual stresses contribute to failure or not depend upon the overall elastic follow-up of the structure which will affect the residual force distribution during the process of crack extension and plastic deformation and applied load the structure is subjected to. In this paper, an overview of importance of elastic follow-up in the structure’s integrity analysis and the benchmark models are presented to study the outcome of stress redistribution, elastic follow-up and residual stresses.

Развитие технологии низкочастотной вибрационной обработки сварных металлических конструкций судо- и машиностроения

Residual welding strains and stresses affect strength, lifetime and reliability of shipbuilding hull structures and a wide spectrum of welded metal structures applied in manufacturing of machine tools, machines and railroad cars, as well as in building industry. Welding strains also increase man-hours required for manufacturing. A traditional way of residual stress mitigation in shipbuilding and other industries is thermal processing which is known to be a costly and labour-intensive operation. An alternative process is low-frequency vibration processing that is relatively easy and highly cost-efficient. Low-frequency vibration processing basically means that metal structures are subjected to alternating-sign loads at resonant or near-resonant frequencies by means of an electromechanical vibration exciter. Size stabilization in this kind of processing is achieved through mitigation and re-distribution of the first-kind residual stresses, i.e. those equilibrating over the entire product or its large elements, so that material structure comes to a more stable equilibrium. This paper discusses SSTC experience in the induction of low-frequency vibration processing of welded metal structures to the practice of shipyards and machine manufacturing enterprises, as well as describes state-of-the-art equipment for its performance and the equipment used to assess and check its results.

The study of redistribution in residual stresses during fatigue crack growth

Numerical and experimental study was conducted on fatigue crack growth (FCG) of metallic components to investigate the redistribution of mechanical residual stresses during FCG. To this end, the compact tension specimens of an aluminium alloy were used. In addition, mechanical residual stresses were introduced near the crack tip by applying compressive and tensile loads, followed by visually observing the side-surface of the specimens to estimate the crack growth length. In the numerical simulation, cyclic J-integral was used as the crack growth fracture parameter and a good agreement was observed between the numerical and experimental results. The results of the finite element method demonstrated a clear redistribution of mechanical residual stresses during FCG. After a few cycles, the residual stress field around the crack tip reached a lower magnitude value confined in a smaller zone, although this zone was stable during the remaining fatigue process. Finally, present study evaluated the effect of stress ratio, load amplitude, and initial residual stresses level on the redistribution of residual stresses. It was observed that the residual stresses are mainly released during the first steps of fatigue loading.

Redistribution of Grain Boundary Misorientation and Residual Stresses of Thermomechanically Simulated Welding in an Intercritically Reheated Coarse Grained Heat Affected Zone

A study of the migration of the grain boundary misorientation and its relationship with the residual stresses through time immediately after the completion of a thermomechanical simulation has been carried out. After physically simulating an intercritically overheated welding heat affected zone, the variation of the misorientation of grain contours was observed with the electron backscatter diffraction (EBSD) technique and likewise the variation of the residual stresses of welding with RAYSTRESS equipment. It was observed that the misorientation of the grain contours in an ASTM DH36 steel was modified after the thermomechanical simulation, which corresponds to the measured residual stress variation along the first week of monitoring, with compressive residual stresses ranging from 195 MPa to 160 MPa. The changes in misorientation indicate that the stress relaxation phenomenon is associated with the evolution of the misorientation in the microstructure caused by the welding procedure. On the first day, there was a fraction of 4% of the kernel average misorientation (KAM) values at 1° misorientation and on the fourth day, there was a fraction of 7% of the KAM values at 1° misorientation.

Redistribution of carbon and residual stress in low-temperature gaseous carburized austenitic stainless steel during thermal and mechanical loading

The effect of thermal annealing and mechanical loading on the redistribution of carbon- and residual stress-depth profiles in low-temperature carburized 316 L austenitic stainless steel was investigated. Gaseously carburized 316 L austenitic stainless steel was strained with a custom-built four-point bending device and isothermally annealed at temperatures in the range 300–500 °C for up to 200 h. Experimental results show that the carburized case is stable at 300 °C and that carbides precipitate only at the highest temperature investigated. At temperatures above 300 °C, the carbon atoms in the carburized case continue to diffuse inwardly, causing an increase of the case depth. Consequently, the surface concentration of carbon, the surface hardness and compressive residual stress change with time. Four-point bending during isothermal annealing accelerates the diffusion-controlled redistribution of carbon over the carburized case for both tensile and compressive side of the strained specimen. Since the carbon-induced volume expansion of austenite during carburizing is accommodated elasto-plastically, a substantial reduction of the carbon content in the surface-near region leads to a change from compressive to tensile residual stresses in the surface region.

Mathematical model and numerical analysis method for dynamic fracture in a residual stress field.

Residual stress field is a self-equilibrium state of stress in the bulk solid material with the inhomogeneous field of the inelastic deformations. The high level of tensile residual stress often leads to dynamic fracture resulting in the instantaneous and catastrophic destruction of the materials because the cracks are fed with the strain energy initially stored in the bulk materials due to the residual stress. The dissipation of the strain energy with crack growth results in the release and the redistribution of the residual stress. In this paper, we propose an effective mathematical model and a numerical analysis method for dynamic fracture in residual stress field. We formulate the dynamic behavior of solid continuum with residual stress field in the context of particle discretization scheme finite element method. This formulation enables the appropriate evaluation of (i) release and redistribution of residual stress due to dynamic propagation of the cracks and (ii) the effect of the elastic wave on crack propagation, which are the most substantial problems on dynamic fracture in residual stress field. We perform the experiments and the simulations of dynamic fracture process in chemically tempered glass sheets with residual stress field to validate the proposed numerical analysis method. The simulation results show remarkable agreement with the experiments of the catastrophic failure of the glass sheets with residual stress field in all aspects of crack behavior. These results indicate that the proposed model and method can rigorously evaluate the release and the autonomous redistribution of the residual stress in the dynamic fracture process.

Simulation of Catastrophic Failure in a Residual Stress Field.

Residual stress has been empirically utilized for industrial applications to control material strength and shape of fragments. The interaction between the dynamically growing cracks and the residual stress field is sufficiently complicated to prevent us from building effective models. To rigorously evaluate the release and redistribution of residual stress in the dynamic fracture process, we develop a mathematical model and a numerical analysis method for the dynamic fracture in a residual stress field. Our methodology is simple and rigorous and applicable regardless of materials and scales.

Effects of heat treatment on mechanical properties of 3D Si3N4f/BN/Si3N4 composites by PIP

The fabrication of three-dimensional silicon nitride (Si3N4) fiber-reinforced silicon nitride matrix (3D Si3N4f/BN/Si3N4) composites with a boron nitride (BN) interphase through precursor infiltration and pyrolysis (PIP) process was reported. Heat treatment at 1000–1200 °C was used to analyze the thermal stability of the Si3N4f/BN/Si3N4 composites. It was found after heat treatment the flexural strength and fracture toughness change with a pattern that decrease first and then increase, which are 191 ± 13 MPa and 5.8 ± 0.5 MPa·m1/2 respectively for as-fabricated composites, and reach the minimum values of 138 ± 6 MPa and 3.9 ± 0.4 MPa·m1/2 respectively for composites annealed at 1100 °C. The influence mechanisms of the heat treatment on the Si3N4f/BN/Si3N4 composites include: (Ⅰ) matrix shrinkage by further ceramization that causes defects such as pores and cracks in composites, and (Ⅱ) prestress relaxation, thermal residual stress (TRS) redistribution and a better wetting at the fiber/matrix (F/M) surface that increase the interfacial bonding strength (IBS). Thus, heat treatment affects the mechanical properties of composites by changing the properties of the matrix and IBS, where the load transfer efficiency onto the fibers is fluctuating by the microstructural evolution of matrix and gradually increasing IBS.

Evaluation of Cyclic Loading Effects on Residual Stress Relaxation in Offshore Wind Welded Structures

Monopile foundations contain welding residual stresses and are widely used in industry to support offshore wind turbines (OWTs). The monopiles are subjected to hammering loads during installation and cyclic loads during operation, therefore the influence of residual stress redistribution as a result of fatigue cycles must be evaluated in these structures. The existing empirical models to predict the residual stress redistribution in the presence of cyclic loading conditions are strongly dependent on the material, welding process and loading conditions. Hence, there is a need to predict the residual stress redistribution using finite element simulations. In this study numerical analyses have been conducted to predict the initial state of residual stress in a simplified weld geometry and examine the influence of subsequent cyclic loads on the relaxation behavior in residual stress profiles. The results have shown that fatigue cycles have a severe effect on residual stress relaxation with the greatest reduction in residual stress values observed in the first cycle. Moreover, the numerical prediction results have shown that the stress amplitude plays a key role in the extent of residual stress relaxation in welded structures.

Regularities of changing the dimensions of the main bore of the cylinder of TMZ-450D diesel engine during the technological process

The article deals with the problems arising during the mechanical and thermal treatment of the TMZ-450D diesel engine cylinder, which is the base part of the engines of small-sized generators and compressors, which are widely used for mobile units in the oil and gas and mining industries. It was found that the metal in the casting has a non-uniform structure, the density of which ranges from 6.75 to 7.25 g/cm3. Redistribution of dislocations and residual stresses in the casting leads to significant changes in the size and shape of the main bore. In addition to the successive changes in size specified by the technology due to the removal of the designated allowance, the dimensions and shape change arbitrarily, uncontrollably in the course of the technological process. It is shown that artificial aging by a thermal method does not provide the desired dimensional stability; therefore, it is proposed to supplement it with natural aging after rough boring for six months. It was revealed that the use of morally and physically outdated equipment makes it necessary to increase the number of finishing operations of honing and, accordingly, to increase the labor intensity of cylinder manufacturing. The use of a two-position boring machine is substantiated, on which the transitions of semi-finishing and fine boring are combined. This completely eliminates the copying of errors that arose when changing the base on previous operations. The use of a two-position modular boring machine ARS-4/Ts of increased accuracy and rigidity significantly increases the accuracy of the bore hole, which makes it possible to reduce the number of honing operations. A variant of the technological process of mechanical and heat treatment is proposed, including natural aging, the use of double boring on a modular boring machine, which will reduce the number of honing operations to one, including rough and finish transitions.

Residual stress analysis of friction stir welded AA6063 pipe butt joint by neutron diffraction technique of ENGIN-X

Residual stress refers to stress that remains in a structure when all applied stresses have been removed. It is important because the combination with applied stress can cause failure at the level below at which the failure could occur. A study has been carried out using the non-destructive neutron diffraction (ND) technique of ENGIN-X to quantify the redistribution of residual stresses in a pipe. A three-dimensional residual stress-measurements test is fully performed on a 89 mm (3.5 in) diameter pipe in AA6063 grade aluminium (5 mm wall thickness) containing a girth friction stir weld. The results have shown an opposite residual stress effect due to tool rotational speed increment especially on the retreating side of the weld. This weld residual stress analysis is an important factor for Fitness-For-Purpose Assessments. This residual stress measurement data provides a basis for structural integrity assessment and inspection planning.

Kontrolisanje zaostalih napona - razvoj najnovijih inženjerskih metoda za merenje bez razaranja i povoljnu preraspodelu zaostalih napona

Welding is used widely in the automotive industry for joining a variety of structural components and parts. Of paramount importance in these structures are their engineering properties, such as fatigue life, distortions, dimensional stability and corrosion resistance that can be affected considerably by the presence of residual stresses (RS). The knowledge of RS and the ability to control their distribution in welded structures is critical when evaluating their fatigue life and preventing catastrophic failures. An engineering concept of residual stress management (RSM) has been developed that addresses all aspects of residual stresses in structural elements. RSM includes three major stages in stress management, i.e. RS determination, RS analysis and RS redistribution. Using this approach, stresses in structures and materials can be evaluated in each specific case either theoretically or experimentally and the performance and fatigue behavior of such structures optimized. This paper is built as an overview of the RSM concept and its application in the fields of non-destructive measurement of residual and applied stresses and in treatment of structures with residual stresses to achieve better performance and longer fatigue life. All three stages of the RSM concept will be discussed and for each of the stages practical engineering approach examples will be given. An example of a project in which the residual stress distribution in a filet welded joint was measured, analyzed and changed by post-weld treatment will be presented to demonstrate the effectiveness of the RSM approach. The advancements in the modern tools used in this project for non-destructive measurement of residual stresses using an ultrasonic computerized complex for residual stress measurement and the ultrasonic peening for redistribution of the residual stresses that allowed improving the quality of the welds and increasing their fatigue life will also be presented.

Cycle Deformation Enabled Controllable Mechanical Polarity of Bulk Metallic Glasses

Tuning anisotropy in bulk metallic glasses, ideally isotropic, is of practical interest in optimizing properties and of fundamental interest in understanding the amorphous structure and its instability. By employing the quasi-elastic asymmetric mechanical cycling method, we effectively induce the mechanical polarity of a model bulk metallic glass, without damaging the sample or introducing significant annealing or rejuvenation effects. Moreover, the polarized anelastic limit can be well controlled by regulating the amplitude of mechanical cycling. Through the atomic-level analysis of nonaffine displacement, we find that only plastic atomic rearranged events corresponding to the training direction can be exhausted by asymmetric cycling and the survived anelastic events dominate the directional anelastic limit. The polarized distribution of local yield stress reveals that the mechanical polarity is attributed to the plastic-event-healing induced asymmetry of local potential energy surface, rather than frozen-in anelastic strain. Furthermore, the healing of plastic events associated with the redistribution of local residual stress indicates the origin of polarity induced by asymmetric cycling. Our study is of fundamental importance, which furthers our understanding of the mechanical deformation of metallic glasses and shed some light on the prospects for improved properties through induced anisotropy.

Simulation of the coupling effect of bulk and induced residual stresses on machining distortion

During high performance machining of large thin walled aluminum aerospace parts, significant distortions become visible. These distortions are due to the effect of the residual stress redistribution, it is therefore critical to understand the influence of residual stresses on machining distortions. This paper presents the prediction of machining distortions on a demonstration part caused due to the combination of bulk and measured induced residual stresses using interpolation techniques into a FE software. The FE model was then compared with CMM data where the FE model predicted the trend and the magnitude with a small difference of around 3%.

FEM study of internal stresses evolution in prestressing strands

This paper describes the results of modeling when the processes of stranding, reduction, straightening and thermo-mechanical treatment (TMT) of prestressing strands were simulated with the help of finite-element method. The distribution of residual stresses used in the simulation models refers to the stresses created at the preliminary stage of wire drawing. The simulation study looked at the effect of thermo-mechanical treatment on the internal wire stresses: residual stresses resultant from the drawing process and further stranding stresses. All studied methods demonstrated a positive effect not only in terms of eliminating internal stresses, but also from the point of view of their redistribution. Reduction of a strand in a solid tool at the ratios of 1–3 % allows to create tensile stresses at the surface of the wire and retain compressive stresses in its core. Straightening in a 5-roller group helped reach a double relaxation in outer wires. TMT, a process combining different physical effects, enabled to control within a broad range the redistribution of residual stresses in steel that was subjected to prior drawing at high deformation ratios. Such residual stresses occur as a result of stranding stresses that accompany the stranding operation and can affect the geometry of the strand. The study showed that tension as a TMT parameter plays a greater role in the elimination of longitudinal residual stresses. That’s why, at the minimum tension, almost no redistribution of residual stresses occur either in the central or in the near-surface layers irrespective of the TMT temperature regime applied. However, when the tension exceeding 70 kN is applied at the temperatures of 380–400 °C, the central and surface residual stresses balance off in the wire or almost disappear. This research was carried out under the Decree No. 220 dated 9th April 2010 of the Government of the Russian Federation (Contract No. 075-15-2019-869 dated 12th May 2019) and was funded by the Russian Science Foundation (Project No. 20-69-46042 dated 20th May 2020) and by the Russian Ministry of Education and Science with the goal of developing high-tech production (contract nos. 02.G25.31.078, December 1, 2015; and MK204895, July 27, 2015).

Re-distribution of residual stress in polymer extrusion: An eccentric approach

The development of residual stresses in plastic pipes due to post-die cooling rate differences of the polymer melt was investigated using concentric and eccentric circular geometries in the shape of an annular tube. Heat transfer simulations were performed to understand the effect of non-uniform wall thickness on the temperature and residual stress profiles of melt solidified polymers. Residual stress measurements and thermal analysis of the end products and heat transfer simulation of the post die cooling process were evaluated to understand the change in stress state in the polymer products as a function of temperature. This was done through an example of extruded high-density polyethylene pipes using an industrial scale extrusion line. The outcome of this research helps better understanding of the melt solidification process and its effect on application related properties in a way that was never presented before.

Theoretical study of the prestressing strand's stress by computer modeling methods

The modern construction industry widely uses reinforced concrete structures, where high-strength prestressing strands are used. Key parameters determining strength and relaxation resistance are a steel microstructure and internal stresses. The aim of the work was a computer research of a stage-by-stage formation of internal stresses during production of prestressing strands of structure 1х7(1+6), 12.5 mm diameter, 1770 MPa strength grade, made of pearlitic steel, as well as study of various modes of mechanical and thermal treatment (MTT) influence on their distribution. To study the effect of every strand manufacturing operation on internal stresses of its wires, the authors developed three models: stranding and reducing a 7-wire strand; straightening of a laid strand, stranding and MTT of a 7-wire strand. It was shown that absolute values of residual stresses and their distribution in a wire used for strands of a specified structure significantly influence performance properties of strands. The use of MTT makes it possible to control in a wide range a redistribution of residual stresses in steel resulting from drawing and strand laying processes. It was established that during drawing of up to 80% degree, compressive stresses of 1100-1200 MPa degree are generated in the central layers of wire. The residual stresses on the wire surface accounted for 450-500 MPa and were tension in nature. The tension within a range of 70 kN to 82 kN combined with a temperature range of 360-380°С contributes to a two-fold decrease in residual stresses both in the central and surface layers of wire. When increasing temperature up to 400°С and maintaining the tension, it is possible to achieve maximum balance of residual stresses. Stranding stresses, whose high values entail failure of lay length and geometry of the studied strand may be fully eliminated only at tension of 82 kN and temperature of 400°С. Otherwise, stranding stresses result in opening of strands.