Cause Of Residual Stresses Research Articles

Numerical simulation of welding residual stresses in 6082-T6 thin aluminum alloy

Thin plate aluminum alloys of the 6082 series are widely used in welded car bodies because of their excellent characteristics such as light weight and high strength. For welded joints, residual stresses significantly affect fatigue strength properties, especially in thin plate welding. In this study, the residual stresses arising from inert gas welding of thin sheet aluminum alloy metals were investigated using numerical simulation techniques. The thermo-elastic–plastic method was used to calculate simulated weld temperature and stress fields. Temperature and stress variations during the welding process were discussed to investigate the causes of residual stresses. The changes in stress during the experimental welding process were tracked, and the results were in agreement with the simulations. The impact of process parameters on welding stress was analyzed through simulation and experimentation. The results showed that residual stress decreases as speed increases and increases as power increases.

Numerical simulation of the residual stress of solid oxide fuel cells with a three-dimensional nonplanar cathode–electrolyte interface

The longevity of solid oxide fuel cells is influenced by internal residual stresses, which may induce deformation or fracturing of components. This study investigates the residual stress distribution at the nonplanar cathode–electrolyte interface by approximating the actual interface with trigonometric functions and developing a three-dimensional (3D) model. The model reveals that the stress patterns at nonplanar interfaces can elucidate the genesis of interfacial cracks. During fabrication, anode contraction results in compressive stress within the electrolyte and tensile stress within the anode, with thermal discrepancies between layers being the primary cause of residual stresses. The reduction process diminishes these stresses, thus enhancing the mechanical integrity of the cell. Mitigating interface nonplanarity is beneficial for minimizing residual stress. At each interface crest, the electrolyte exhibits a local minimum in compressive stress, and a local maximum in shear stress occurs between each crest and trough. Furthermore, decreasing the initial porosity and NiO volume fraction can slightly lessen interlayer thermal discrepancies, with little effect on residual stresses.

Hyperelastic constitutive relations for soft elastomers with thermally-induced residual stress

Residual stress widely exists in soft materials. Besides growth, inhomogeneous thermal expansion is also a primary cause of residual stress. However, establishing a proper hyperelastic constitutive relation is a great challenge since the existing theories cannot capture the change of underlying mechanical responses triggered by temperature variations. In this paper, a general hyperelastic constitutive relation for soft elastomers with thermally-induced residual stress is developed. We first reveal the initial temperature dependence of conventional thermoelastic models. This property attributes the alteration of the underlying thermoelastic response to free thermal expansions. Then, a compatibility-broken curvature compensation (CBCC) framework is established based on finite thermoelasticity. It generates a free thermal expansion to eliminate the Riemannian curvatures of the virtual stress-free configuration derived from the isothermal stress release. Such a mechanism indicates the non-local effect of the residual stress, which fundamentally modifies the traditional view that invariant formulations cover all the possible functional dependence of residual stress. Also, the obtained governing equations are similar to Einstein field equations of the general theory of relativity. This similarity may deeply imply a standard mechanism concerning the curvature compensation leading to residual stress genesis. We finally conduct comparative analyses of the spherically symmetric and axisymmetric problems between the current constitutive relation and the existing models. The influences of adopting distinct residual stresses, the performance of the non-local effect, and the availability of the new constitutive relation are investigated in detail. This framework can shed some light on the constitutive modeling of soft materials.

Literature Review on Thermomechanical Modelling and Analysis of Residual Stress Effects in Wire Arc Additive Manufacturing

The wire arc additive manufacturing (WAAM) process is a 3D metal-printing technique that builds components by depositing beads of molten metal wire pool in a layer-by-layer style. Even though manufactured parts commonly suffer from defects, the search to minimize defects in the product is a continuing process, for instance, using modeling techniques. In areas where thermal energy is involved, thermomechanical modeling is one of the methods used to determine the input thermal load and its effect on the products. In the WAAM fabrication process, the thermal load is the most significant cause of residual stress due to the extension and shrinkage of the molten pool. This review article explores the thermomechanical effect and stress existing in WAAM-fabricated parts due to the thermal cycles and other parameters in the process. It focuses on thermomechanical modeling and analysis of residual stress, which has interdependence with the thermal cycle, mechanical response, and residual stress in the process during printing. This review also explores some methods for measuring and minimizing the residual stress during and after the printing process. Residual stress and distortion associated with many input and process parameters that are in complement to thermal cycles in the process are discussed. This review study concludes that the thermal dependency of material characterization and process integration for WAAM to produce structurally sound and defect-free parts remain central issues for future research.

TESTING AND DIAGNOSTIC COMPLEX FOR GREENHOUSE EQUIPMENT

Designing of technological processes of volume stamping at the modern level involves solving a number of complex problems. The main purpose of the article is to use the laws of the deformation process to model the kinematics of plastic flow using modern software systems based on the finite element method. The obtained data will allow to form an information field of a specific technology and, thus, to be able to control both the process and the properties of products. These tasks include: determining the degree of deformation in the volume of the body and predicting the technological heredity of products; optimization of stamping transitions and prevention of technological failures. As a result of plastic deformation, especially cold, the material inherits uneven hardening and heterogeneity of properties in the volume of stamped products, which are the cause of residual stresses. Residual stresses can increase or decrease the strength of the product if it is not subjected to heat treatment after cold plastic deformation. The heterogeneity of the properties is due primarily to the uneven distribution of the accumulated deformation, the calculation of which in conventional technological practice is complicated. After pressure treatment, parts or workpieces are often annealed to relieve internal stresses and improve the structure of the metal. When designing technological processes with the use of computer modeling programs for plastic deformation processes, it is possible to choose such modes of deformation, which excludes the area of deformation that causes technological failures. In the processes of cold three-dimensional stamping, the possibilities of plastic deformation of metals are limited. Very often the deformations required to obtain products of the desired shape exceed the plasticity of the material - the degree of deformation at which a crack is formed under the conditions of this mechanical scheme of deformation. Therefore, it is necessary at the design stage of technological processes to establish whether the material will withstand the projected operation, which will lead to intensification of metalworking processes by pressure, as well as significant savings associated with reducing production experiments to adjust the process. Modern theory of plasticity allows to formulate and solve all these problems, however, given their complexity and connectivity, the result can be achieved only by using direct numerical methods, which in combination with high-speed computer equipment have created the preconditions for mathematical models of metalworking pressure and led to the emergence of appropriate programs, based in most cases on the finite element method.

PECULIARITIES OF APPLICATION OF ONE AND TWO-DIMENSIONAL FINISHED ELEMENTS IN MODELLING KINEMATICS OF PLASTIC FLOW OF METAL

Designing of technological processes of volume stamping at the modern level involves solving a number of complex problems. The main purpose of the article is to use the laws of the deformation process to model the kinematics of plastic flow using modern software systems based on the finite element method. The obtained data will allow to form an information field of a specific technology and, thus, to be able to control both the process and the properties of products. These tasks include: determining the degree of deformation in the volume of the body and predicting the technological heredity of products; optimization of stamping transitions and prevention of technological failures. As a result of plastic deformation, especially cold, the material inherits uneven hardening and heterogeneity of properties in the volume of stamped products, which are the cause of residual stresses. Residual stresses can increase or decrease the strength of the product if it is not subjected to heat treatment after cold plastic deformation. The heterogeneity of the properties is due primarily to the uneven distribution of the accumulated deformation, the calculation of which in conventional technological practice is complicated. After pressure treatment, parts or workpieces are often annealed to relieve internal stresses and improve the structure of the metal. When designing technological processes with the use of computer modeling programs for plastic deformation processes, it is possible to choose such modes of deformation, which excludes the area of deformation that causes technological failures. In the processes of cold three-dimensional stamping, the possibilities of plastic deformation of metals are limited. Very often the deformations required to obtain products of the desired shape exceed the plasticity of the material - the degree of deformation at which a crack is formed under the conditions of this mechanical scheme of deformation. Therefore, it is necessary at the design stage of technological processes to establish whether the material will withstand the projected operation, which will lead to intensification of metalworking processes by pressure, as well as significant savings associated with reducing production experiments to adjust the process. Modern theory of plasticity allows to formulate and solve all these problems, however, given their complexity and connectivity, the result can be achieved only by using direct numerical methods, which in combination with high-speed computer equipment have created the preconditions for mathematical models of metalworking pressure and led to the emergence of appropriate programs, based in most cases on the finite element method.

Identifying the causes of residual stress in polycrystalline diamond compact (PDC) cutters by X-Ray diffraction technique

An attempt was made to identify the sources of residual stress in polycrystalline diamond compact (PDC) cutters by X-ray diffraction (XRD) technique. PDC retains residual stress after sintering and this residual stress plays an important role for cutter performance. X-ray diffraction method of residual stress measurement is very common because it is nondestructive. Residual stress was measured in a finished 16 mm PDC cutter and changes in residual stress were observed as the substrate was removed by grinding. Residual stress was also measured after full removal of cobalt from the diamond table by leaching. Comparison was made between the as-pressed PDC cutter, after removing the substrate, and after removing the cobalt to understand the relative contribution of geometry and cobalt binder to overall residual stress. An additional measurement was made under High Pressure High Temperature (HPHT) compacted diamond powder in the absence of cobalt to evaluate the contribution of high temperature deformation of diamond particle on residual stress.

Causes of residual stresses during machining of workpiece surfaces

The basic data about residual stresses are considered, and the classification of residual stresses that occur in the surface layer of parts is provided. At the moment, it is customary to divide residual stresses by the volume of balancing into macro-stresses, micro-stresses and submicron stresses, and by the sign — compressive and tensile. The main causes of residual stresses are analyzed, and the factors influencing their occurrence are identified. There are three main causes of residual stresses: uneven plastic deformations in the cutting zone, as a result of the force of the tool on the workpiece, high temperatures accompanying the cutting process, and structural and phase transformations occurring on the surface of the workpiece.

Analysis of residual stresses in rails during the straightening process

The straightening process is the main cause of residual stresses in the manufacture of rails. It is a non-trivial process with cyclic plastic loads, solid–solid contact and complex geometry, which computational simulation is often complex and time-consuming. In this work, a new methodology was developed by means of a quasi-static modeling instead explicit dynamic. This methodology was proved to be effective and fast. Sixteen cases were simulated, and a C-shaped pattern for longitudinal stress, as seen through the literature, was obtained in the most of them, even with large variations between the main parameters: the yield strength, the tangent modulus and the initial curvature of the rail. The longitudinal normal residual stresses were higher than the transversals ones, as expected. The results obtained by simulations were the basis for the use of a Gaussian process regressor to predict the residual stresses from any initial parameters. This tool confirmed that the parameters that more affect the final state of residual stresses are, in this order, yield strength, tangent modulus and curvature. This is relevant information, since the hardest data to obtain in practice are the initial curvature of rail. Both simulation methodology and the statistical Gaussian process tool could be useful to perform life fatigue analysis in rails, since this needs the initial state of residual stresses to be more reliable.

Multi-Scale Modeling of Curing Residual Stresses in Composite with Random Fiber Distribution into Consideration

During curing process of composites, residual stresses inevitably develop and play an important role in the final mechanical properties of composites. Therefore, the consideration of residual stresses when designing composite structure is necessary. The causes of residual stresses are well known on the part and fiber-matrix level. However, the influence of the part level factors on micro residual stresses is less known and rarely investigated. This work aims at a better understanding of the effects of macro-level factors, including temperature variation and mechanical strains on micro-scale stresses. To this end, a multi-scale method is developed, which consists of a macro-scale model to capture temperature variation and mechanical strains field under a given cycle condition, and a RVE (Representative Volume Element) to predict residual stresses in matrix. The results demonstrate that the maximum micro residual stress in matrix presents about almost 52% reduction in the model with part-level information into consideration as compared with the results without considering the multi-scale effect. It can be also seen that with multi-scale effect into account, the matrix in the RVE experienced tensile residual stresses in the matrix-poor locations and compressive residual stresses in the matrix-poor locations.

Research progress of residual stress determination in magnesium alloys

Abstract With the research development of the magnesium alloys, the deformation or stress corrosion induced by residual stress (RS) attracted extensive interests in industry and research efforts extensive. However, there are relatively few studies on the RS of magnesium alloys in the world. The generation cause of RS in magnesium alloys was analyzed at first. Several methods of determinate the RS, including destructive methods (drilling hole, crack compliance, layer exfoliation etc.) and non-destructive methods (X-ray Diffraction, Neutron Diffraction, Short Wavelength X-ray Diffraction) were summarized. The factors that influence the measuring accuracy of XRD method were emphasized. The research trends of RS in magnesium alloys were put forward.

Effect of Heat Treatment on Residual Stresses in the Zone of Fusion of Austenitic and Vessel Steels

The effect of heat treatment on the structure and physical and mechanical properties of flat specimens cut from a massive billet from steel 15Kh2MFA with an austenitic facing on one side is studied. The hardness and the microhardness of the specimens are determined. Acoustic and x-ray studies are performed. The causes of residual stresses giving rise to deformation and formation of cracks in the faced steel are established. Ways to solve the problem are suggested.

변형지그를 이용한 폴리카보네이트 시편의 케미컬 크랙킹 및 응력측정에 관한 연구

사출성형품의 잔류응력 형성의 원인은 사출성형공정 중 재료가 받는 높은 온도변화와 전단응력이다. 케미컬 크랙킹 테스트는 잔류응력을 측정하는 방법 중의 하나이며 크랙은 잔류응력의 크기에 따라 형성된다. 본 연구에서는 시편이 받고있는 응력과 케미컬 크랙킹과의 관계를 연구하였다. 변형지그를 설계하고 이를 이용하여 시편에 변형을 주어 응력을 가하였다. 시편은 폴리카보네이트를 이용하여 핫 프레스로 제작하였고 시편의 제작 중에 형성된 잔류응력을 제거하기 위해 어닐링을 하였다. 시편을 변형지그에 고정시키고 시편에 크랙을 유도하기 위해 이를 솔벤트에 담궜다. 솔벤트는 tetrahydrofuran과 methyl alcohol을 이용하여 제조하였다. 시편에서 변형에 따라 응력이 증가할수록 크랙의 빈도수와 밀도가 증가하였다. 본 연구의 결과는 케미컬 크랙킹 방법으로 폴리카보네이트 사출성형품의 잔류응력을 정량적으로 측정하는데 활용될 수 있다. The causes of residual stress in an injection molded part are high temperature variation and shear stress during molding process. Chemical cracking test is one of the methods of measuring residual stress and cracks are developed according to the degree of residual stress. In this study, the relationship between chemical cracking and exerted stress have been investigated. Deformation jig was designed and used to give a stress through deformation in a specimen. Specimens were molded by a hot press using polycarbonate (PC) and annealed to remove residual stresses in the specimens. Specimens were fixed in the deformation jig and immersed into the solvent to create cracks in the specimens. Solvents were prepared by using tetrahydrofuran and methyl alcohol. As stress accordance with the deformation in the specimen increased, the frequency and density of cracks in the specimen also increased. The results of this study can be used for the measurement of residual stress quantitatively in an injection molded PC product using a chemical cracking method.

Ремонт корпусов насосных агрегатов из стали 20ХГСФЛ с применением сварочных технологий

20CrMnSiVaL low-alloy cast steel is widely used for tanks, machines and devices (pumps, compressors, hydraulic boxes and other) in the oil and gas industry. A large amount of such equipment operates under conditions of high pressure, corrosive effect of the working environment, a large temperature difference, mechanical loading due to moving parts. During its operation the elements of oil and gas are eroded due to temperature and power loads, corrosion, and other factors. Most constructive elements of gas and oil equipment are repaired by welding. А highly concentrated heat source and deformation capacity are the cause of residual stresses. They affect the performance and accuracy of manufacturing elements. One of the main problems concerning the improvement of the quality of machines is the enhancement of housing repair technology. The housings are made of cast steel using electric arc welding. In this work we employed the finite element method in the program ANSYS. We performed an analysis of stress-strain state in the model of the welded joint simulating the machine body. We considered and implemented the technology of repair by welding and different types of treatment. We conducted a comparative study of mechanical properties. In this paper we also present the results of residual welding estimation in samples welded using various technologies. We compared traditional technologies of heat treatment and deformation processing – ultrasonic and vibration treatment.

Evaluation of residual stress near the weld overlay cladding by welding and post-weld heat treatment

Austenitic stainless steel is welded as a cladding on the inner surface of a reactor pressure vessel (RPV) made of low alloy steel. In order to assess the structural integrity of the RPV precisely, the residual stress distribution caused by weld-overlay cladding and post-weld heat treatment (PWHT) is evaluated. Since the cladding layer is very thin compared to the vessel wall, it is necessary to evaluate the residual stress distribution around the weld fusion line, which can be very steep. In this study, cladded specimens were fabricated using different welding methods. Residual stress measurements using both sectioning and deep hole drilling (DHD) methods were then performed to evaluate the residual stress distributions through the weld fusion line. Three-dimensional thermal-elastic-plastic-creep analyses based on the finite element method were also conducted to evaluate the residual stress caused by weld-overlay cladding and PWHT. It was shown that analytical results provided reasonable agreements on weld residual stress with experimental results. It was also clarified that the main cause of residual stress due to welding and PWHT was the difference of thermal expansion between weld and base metals.

Segmental Relaxations have Macroscopic Consequences in Glassy Polymer Films

We have investigated the consequences of physical aging in thin spin-coated glassy polystyrene films through detailed dewetting studies. A simultaneous and equally fast exponential decay of dewetting velocity, width, and height of the rim with aging time was observed, which is related to a reduction of residual stresses within such films. The temperature dependence of these decay times followed an Arrhenius behavior, yielding an activation energy of 70±6 kJ/mol, on the same order of magnitude as values for the β-relaxation of polystyrene and for relaxations of surface topographical features. Our results suggest that rearrangements at the level of chain segments are sufficient to partially relax frozen-in out-of-equilibrium local chain conformations, i.e., the cause of residual stresses, and they might also be responsible for macroscopic relaxations at polymer surfaces.

Analysis of the Surface Residual Stress in Grinding Aermet100

Grinding induces residual stresses, which can play an important role on the fatigue of the component. In general, residual stresses in a ground surface are primarily generated due to three effects: thermal expansion and contraction during grinding, plastic deformation caused by the abrasive grains of the wheel and phase transformations due to high grinding temperature. It was found that thermal expansion and plastic deformation in the grinding process were the major causes of residual stresses. In this paper, an analysis model for the calculation of residual stresses induced by a surface grinding process on an ultrahigh-strength steel (Aermet100) workpiece is presented. Firstly, the stress distribution induces by thermal expansion was obtained base on the transient heat conduction equation and the thermal properties of Aermet100. All the calculations were based on the moving heat source solution which was modeled as a uniformly distributed, 2D heat source moving across the surface of a half-space, found in Carslaw and Jaeger. The results show that the near surface residual stress is predominantly tensile and that the magnitude of this stress increases with increasing heat flux values. Secondly, the plastic deformation caused by the abrasive grains of the wheel was simulated base on the grain-workpiece interaction. The chip formation process and the material removal mechanisms can be examined using the micro-scale approach. The results show that the residual stress induced by the grinding force itself is generally compressive which is smaller than the residual tensile stress induced by thermal stress. Therefore, the residual stress brought about by grinding operation is generally a tensile stress. This paper offers an insight into the mechanism understanding of thermal and mechanical residual stresses induced by surface grinding. Key words: grinding, residual stress, grain

The Study of Residual Stress in Welded Specimens of Aluminium Alloy by Using Acoustic Emission Method

Welding is one of the most significant causes of residual stresses and typically produces large tensile stresses whose maximum value can be approximately equal to the yield strength of the materials being joined. These large tensile stresses are often responsible for premature component failure. Metallurgical welding joints are extensively used in the fabrication industry, including ships, offshore structures, steel bridge, and pressure vessels. In this study, residual stresses in welded specimens of AL–6061 were evaluated by using ACOUSTIC EMISSION method which is one of the nondestructive tests. In this work, AE signals formed during the tensile test of welded specimens were investigated. The results show that AE signals in specimens which have large amount of residual stress were detected in less load.

Analysis of Residual Stress Development during Thermal Processing of AL-SI Alloys

Residuals stresses can be present in almost every industrial component. Manufacturing processes such as casting, welding, and heat treatment are the most common causes of residual stresses. Thermal residual stresses could be developed in a component during heat treatment process as a result of non-uniform heating or cooling operations. In this study, experiments were carried out to develop insights into and understanding of the residual stresses that can arise during thermal treatments of Al-Si components. Due to the complexity of residual stresses analysis in real components, a common mixed-section casting was employed. In order to fulfill the requirements of performing different thermal treatments, a special cooling apparatus was designed and built. A number of the casting components of an Al-Si alloy were annealed for stress relief, and then removed from the furnace and cooled with different water flow rates. Then, the amount of accumulated residual stresses in the components was measured relaxation of stress using cutting. Thermal analysis and residual stress measurement for different thermal treatment regimes showed that by choosing a specific holding temperature before direct cooling, the value of residual stress increases linearly with flow rate of cooling. On the other hand, for a constant value of cooling water flow, ∆Tmaxand residual stress level decreases when the value of base temperature of furnace decreases. Moreover, the cutting method can be a suitable method for measuring thermal residual stresses in Al-Si components and thermal analysis is a powerful technique to predict residual stresses.

原子炉圧力容器肉盛溶接部における溶接及び溶接後熱処理による残留応力分布評価

Austenitic stainless steel is welded as a cladding on the inner surface of a reactor pressure vessel (RPV) made of low alloy steel. In order to assess the structural integrity of the RPV precisely, the residual stress distribution caused by weld-overlay cladding and post-weld heat treatment (PWHT) is evaluated. Since the cladding layer is very thin compared to vessel wall, it is necessary to evaluate the residual stress distribution around the weld fusion line can be very steep. In this study, cladded specimens were fabricated using different welding methods. Residual stress measurements using both sectioning and deep hole drilling (DHD) methods were then performed to evaluate the residual stress distributions through the weld fusion line. Three-dimensional thermal-elastic-plastic-creep analyses based on finite element method were also conducted to evaluate the residual stress caused by weld-overlay cladding and PWHT. It was shown that analytical results provided reasonable agreements on weld residual stress with experimental results. It was also clarified that the main cause of residual stress due to welding and PWHT was the difference of thermal expansion between weld and base metals.