Calculation Of Residual Stresses Research Articles

Calculation method and analysis of residual stress in the strip bending roller straightening process

Taking thin gauge strip as an example, the deformation process of metal strip in bending roll straightening was studied. Based on the theory of discrete, curvature integral and elastic–plastic mechanics, the strip travel trajectory of the bending roll straightening process is analyzed, and the numerical analytical calculation method of the continuous straightening process of the strip bending roll is established. The results are verified by establishing MARC finite element simulation and designing straightening experiment. The effects of yield strength, plastic rate and bending amount on residual stress after straightening were studied. In the straightening process, with the increase of the amount of bending roll, the residual strain converges to the region Γ, and with the increase of the yield strength, the region Γ decreases. With the increase of the yield strength, the amount of bending roll and the plastic rate, the wave height increases. The results of the calculation of residual stress, finite element simulation and experiment are close and the trend is consistent. The results show that the logic of the calculation method is reasonable, and the prediction error is within the scope of engineering application, which is helpful to the realization of process intelligence in the process of bending roller straightening.

Exploring the possibility of undesirable manufacturing heritage reduction in parts made of composites and their joints

The object of the research is the possibility of improving the quality of parts made of composites (CM) by means of pre-polymerization treatment of the wet package with intensive pulse loading. The existing technologies for forming parts from CM involve the compaction of the collected impregnated package of reinforcement layers and their subsequent polymerization under the influence of pressure and temperature. As a result of this technology, residual thermal and shrinkage stresses occur in the composite package, which lead to undesirable spatial deformations of profile parts, a violation of monolithicity in the areas of the connection of the composite and metal ends. Using the example of an angular composite profile with a profile with doubler on one of the caps, the residual stress calculation is given and the method of choosing rational angles for stacking the reinforcing material is demonstrated in order to reduce the amount of residual thermal stresses that arise in the composite during its polymerization. The dependence of the twisting parameter of a long-dimensional composite profile of constant cross-section along its axis on the modulus of elasticity and the coefficient of linear temperature expansion is plotted. The work explains the mechanism of the emergence of such harmful technological heredity. The value of the residual deformations was estimated. Based on the analysis of the impregnation process of dry reinforcing material with a binder, the task of increasing the maximum contact area of the binder with fibers is formulated and a possible method of its increase is analyzed. Thus, using the model of capillaries between the fibers of the composite, it is concluded that it is necessary to apply additional pressure to the binder for its deeper advancement between the fibers. Using a synergistic method of combining knowledge from various branches of industry and based on experimental data, a process of pre-polymerization loading of the impregnated package with intense impulse loading (shock waves) is proposed. This process greatly improves the quality of parts of the units produced.

Optimization of large cast Haynes 282 based on thermal induced cracks: formation and elimination

Haynes 282, a wrought material, attracts the attention from casting application due to its excellent mechanical properties. Fracture of large cast Haynes 282 were found before yielding during tensile test in previous researches, but the reasons have not been fully understood. In this study, various heat treatments were designed and applied for large cast Haynes 282 to reveal the fracture before yielding. Thermodynamic calculation, residual stress calculation combined with microstructural examination were utilized to analyze the reasons of fracture. It has been found that there are grain boundary cracking and grain boundary precipitate cracking in the tensile sample. The grain boundary cracking is mostly attributed to the melting of the low melting point phases such as some segregated matrix and μ phases. The grain boundary precipitate cracking is associated with the blocky Ti, Mo rich MC carbides, and it is more likely to be caused by the quenching after the second homogenization treatment. Optimized heat treatment has been proposed and proven to be workable for the large cast Haynes 282.

A structured approach to the determination of residual stresses in an epoxy-amine coating and the influence of thermal ageing on the thermomechanical properties, residual stresses and the corresponding failure modes of coating

The purpose of this research was to develop a structured approach for the calculation of residual stresses in organic coatings through the experimental determination of thermomechanical properties of the epoxy-amine coating. The feasibility of this proposed method was validated by the presence of cracks on epoxy amine coating subjected to isothermal ageing at 180 °C for a period of 8 weeks, followed by thermal shock by water quenching at 0 °C, when the tensile strength of coating (8.00 MPa) was surpassed by the accumulated residual stress in the coating (9.66 MPa). The influence of thermal ageing on the thermomechanical properties, residual stresses and the corresponding failure modes were also evident. Significant variation of thermomechanical properties such as the increase in Tg from 77.60 °C to 120.50 °C, reduction of thermal expansion coefficient from 51.74×10−6°C−1 to 40.27×10−6°C−1, reduction of elastic modulus from 1600 MPa to 1400 MPa, and reduction of ultimate tensile strength from 27.00 MPa to 8.00 MPa after thermal ageing were observed. These variations have ultimately led to the increase of residual stresses in coatings that has resulted in the formation of cracks.

Metal-Cored Arc Welding of I-Profile Structure: Numerical Calculation and Experimental Measurement of Residual Stresses

In this study, numerical and experimental research of residual stresses was carried out on an I-profile structure model and welded by using the Metal-cored Arc Welding (MCAW) technique. The numerical research was carried out by sequential simulation, using the birth and death element in the thermal analysis, while the same was omitted in the mechanical analysis in order to speed up the calculation process. The measurement of residual stresses was conducted on the outer surfaces of the model at a depth of 0.015 mm below the surface. It was determined that the longitudinal stresses in the weld and its immediate surroundings are tensile, while towards the ends of the model, they change to compressive. Transversal residual stresses exist mainly around the weld itself, and the immediate surroundings and decrease towards the ends of the model. A high agreement between the numerical and experimental results was found.

Topology optimization of continuous fiber-reinforced composite (CFRC) structures considering the residual stress in additive manufacturing

This work proposes a topology optimization method for continuous fiber-reinforced composite (CFRC) structures with additive manufacturing (AM), which realizes the concurrent optimization of material layout and fiber orientation. The residual stress caused by AM process is constrained to avoid the failure of warpage and distortion. The inherent strain method (ISM) is applied to simplify the calculation of residual stress, the Tsai–Wu criterion and P-norm are incorporated to realize structural failure prediction and local constraint aggregation. Several typical instances are adopted to verify the effectiveness of proposed method, which provides a novel solution for the optimization of CFRC structures fabricated by AM.

The impact of residual technological stresses on the opening and stability of through cracks in pipeline elements

The impact of residual stresses in a DN850 pipe (steel 10GN2MFA) with austenitic cladding, welding stresses in the mounting annular seam of the pipeline, and residual stresses arising in a curvilinear branch DN350 (steel 08Kh18N10T) during manufacture by plastic deformation on the opening and stability of through cracks is considered. Calculations of residual stresses are performed using the finite element method (FEM). It is shown that residual stresses cause a change in the size and shape of the outflow channel, the coolant flow rate, and the value of the J-integral at the crack tip. In case of short cracks and relatively low operating stresses, the crack edges can close on the inside of the pipe wall due to the action of residual stresses thus leading to a decrease or cessation of the leak. A reversed effect of residual stresses on extended cracks is observed at rather high operating stresses: change in the shape of the outflow channel (an increase in the opening of the crack edges on the outer surface of the pipe) leads to a decrease in the friction of the coolant flow against the crack edges and, hence, to an increase in the leak volume. The results of testing full-scale models of elements of a straight section of the pipeline with a welded seam and a curvilinear branch DN350 with artificially created defects by internal pressure and bending moment are presented. It is shown that local through cracks develop from initial defects, which remain stable at maximum design loads (normal operating conditions plus maximum design earthquake) which matches the calculation results and meets the requirements of the applicability of the concept of «leak before break».

Analysis of Longitudinal Cracks of Casing in Heavy Oil Thermal Recovery Well

This paper investigates cracking failure of the casing tube. There were longitudinal cracks in the heavy oil thermal recovery well occurred in an oil field. The fracture cause of casing was analyzed by macrographic observation, chemical composition analysis, mechanical property test, metallographic analysis, scanning electron microscope (SEM) and residual stress calculation. The results showed that the crack of the failed casing originates from the external surface of the pipe and has the characteristic of intergranular propagation. The fracture characteristics are brittle fracture. The conclusion showed that stress corrosion cracking(SCC) is the main cause of longitudinal crack of casing in the heavy oil thermal recovery well. Under the combined action of external corrosive media and internal stress, SCC cracks are generated on the surface of casing, and the cracks propagate along grain boundaries and finally lead to cracking and failure of casing. Some recommendations were proposed to avoid similar failures.

DETERMINATION OF RESIDUAL STRESSES IN PIPES

During production, operation, transportation, and aging of finished products, stresses occur in the pipe metal. As a rule, these residual stresses affect the quality of pipes. The presence of residual stresses in products can cause brittle fracture, cracking due to corrosion, reduced elasticity, warping, etc. The development of methods for managing residual stresses in metals and products is the realization of a powerful reserve for improving the quality of metal products, which means increasing the reliability of machinery. The question arises as to which method, convenient in production conditions, should be used to assess residual stresses. A simple and affordable method for estimating residual stresses is needed in production conditions. This paper presents a simplified method for estimating residual stresses in pipes. The purpose of the work is to improve and present a methodology for estimating tangential and axial residual stresses in cold-formed pipes and tubes after heat treatment according to the method of M.M. Davydenko. Research methods: M.M. Davydenko's method for cutting rings and cutting strips from pipes. Calculation of residual stresses. Results. The method for estimation of tangential and axial residual stresses in pipes after cold deformation and after heat treatment is improved and presented. The formulas for calculating residual stresses are given. Practical value. Pipe plants need to estimate residual stresses to develop technological processes for the manufacture of new types of pipes and to meet pipe standards. The improved and presented methodology will help manufacturers in assessing residual stresses. Conclusions. Modern methods for assessing residual stresses have been considered. A methodology for calculating tangential and axial residual stresses according to M.M. Davydenko by cutting rings and cutting strips from the metal of the studied pipes is presented. The methodology is officially registered, which allows it to be used for official assessment of pipe quality.

Methods to reduce residual welding stresses in mining excavator metal structures

Residual stresses in metal structures of mining machinery caused by welding occur due to simultaneous uneven heating and cooling of local sections of structures, variable cooling rates in the different areas of the weld and deformations caused by metallurgical phase transformations. Residual stress in the welded joint can significantly increase the external load that can lead to structural failure. Research on the calculation, measurement and relief of residual stresses under welding is an important issue when predicting the service life of metal structure units of mining machinery and equipment. An accurate quantitative estimation of residual stresses in welded products, repair welds included, as well as the search for the fundamental principles of the elimination methods of residual deformations are of considerable practical interest, which is relevant for the authors of this paper. The study involved a general review of the latest researches in the field of estimation and measurement of residual stresses caused by electrogas welding. It has been proposed to use various techniques and analytical methods for quantitative estimation of welded joint residual stresses on the basis of fracture mechanics, which enabled to take preventative measures at early stages to reduce the cost of repair and maintenance of welded metal structures of mining excavators. The conducted study resulted in formulating the proposals on relief of residual welding stresses in the metal structures of mining excavators.

Numerical Simulation of the Welding Process during the Main Circulation Pump Impeller Repair

Paper presents a numerical simulation of the main circulation pump impeller damaged parts repair/replacement welding process, for the prediction of welding-induced residual stresses. 3D numerical model creation of the impeller flange and central hub welded joints. Thermal and stress-strain analysis of assessed parts using the finite element method. Calculation of equivalent residual stresses in the area of examined welded joints. Applicability of results in further impeller integrity analyzes. The results confirmed the suitability of the chosen welding procedure and technology.

Experimental research and numerical analysis of welding residual stress of butt welded joint of thick steel plate

The thickness of steel plates used in the member has gradually increased to meet the load-bearing capacity requirements of long-span steel bridges. As the primary connection method of thick steel plate, welding will result in considerable welding residual stress with complex distribution. Large welding residual stress will significantly impact the performance of steel bridges. In this paper, the distribution of residual stress in welded thick steel plate is systematically studied, a specimen with a thickness of 80 mm was designed and fabricated, and the welding residual stress was measured by X-ray diffraction. The finite element model was established and verified by test results. Subsequently, the finite element calculation of the welding residual stress of steel plates with thicknesses of 20, 40, 60, 80, and 100 mm was carried out, and the distribution of surface residual stress and the influence of plate thickness on residual surface stress were studied; then the spatial evolution mechanism of welding residual stress was studied, and the distribution of residual stress inside steel plate and the influence of plate thickness on the distribution of residual stress were revealed. The results show that the surface and internal residual stresses of 20–100 mm thick plates have good symmetry on the paths perpendicular to the weld seam, and asymmetry only occurs in the weld seam and heat-affected zone where the stress fluctuates. On the paths perpendicular to the weld seam, the stress in the X direction transitions from the “M” shape distribution on the surface to the “Π” shape distribution inside for 20–40 mm thick plates, and the residual stress near the weld seam gradually changes from compressive to tensile; The distribution of stress in the X direction in the 80–100 mm thick plate has experienced the transition from “M” shape to “Π” shape to “M” shape, and the stress near the weld seam has experienced the transition from compressive to tensile to compressive. The stress change in the X direction of the 60 mm thick plate is between the above two cases. On the path of internal stress along the thickness, the maximum stress in the X direction is 310–400 MPa for 20–40 mm thick plates, which appears at about 1/2 plate thickness. The maximum stress in the X direction for 60–100 mm thick plates is 400–480 MPa, which appears at 0.2–0.3 times the thickness of the plate from the upper surface. The results could serve as a reference for welding residual stress analysis and guide optimization design of steel bridges made of thick steel plate.

NDT of Residual Stress in Thick Aluminum Alloy Plates under Different Aging Conditions Using Multiple Techniques.

In this paper, a portable residual stress tester and synchrotron radiation diffraction technique were used to measure the residual stress distribution of thick 2A14 aluminum alloy plates under different aging conditions after solution treatment. The stress changes after solution and aging were analyzed using metallographic structure observation, electron backscattered diffraction (EBSD), X-ray diffraction (XRD), and other characterization methods. The results show that after solution treatment at 500 °C and aging at 170 °C, the second phase precipitates, lattice distortion is released, and the stress level gradually decreases with aging time. The residual stress of the plate comprises compressive stress; there is stress concentration in the central area. The stress distribution obtained by the two residual stress calculation methods, cosα and sin2ψ, under different process conditions was consistent.

Rapid calculation of part scale residual stress – Powder bed fusion of stainless steel, and aluminum, titanium, nickel alloys

A novel analytical model is developed to compute the part scale through-thickness longitudinal residual stress distributions and applied for laser powder bed fusion of four commonly used powder alloys. An important input for the analytical modeling calculations is the peak residual stress for a deposited layer, which is estimated using a unique functional relationship and presented as a function of important process conditions for laser powder bed fusion of different powder alloys. The analytically calculated results of longitudinal residual stress distributions through the part and baseplate thickness are tested rigorously with the corresponding numerically computed and experimentally measured results in the literature for laser powder bed fusion of small and large parts involving the deposition of several thousands of layers. It is shown further that the analytical model can serve as a fast and practical design tool to estimate the through-thickness longitudinal residual stress distribution, which is along the length of the part, for part scale laser powder bed fusion using inexpensive computational resources and with appreciable accuracy. The raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations. • An analytical model for residual stresses in 3D printed parts is extensively tested. • The model is validated with experimental data and numerically computed results. • Residual stresses in large 3D printed parts of 5 alloy compositions were examined. • Powder-specific process maps of peak tensile residual stresses are presented.

In-situ Primary Stress Detection Based on Seismic Tomography Measurements and Numerical Back-analysis for an Underground Radwaste Repository

In order to understand how the in-situ primary stress state has evolved with subsidence and uplift in a granitic rock mass for anticipated of a radioactive waste repository in Hungary, the authors investigated the applicability of seismic tomography as an interpretive tool. Very high P wave velocity (Vp) values were obtained during the tomographic scanning of the study area of the repository, and these were compared with existing findings of in-situ and laboratory seismic measurements.Apart from seismic tomographic survey, dynamic FEM numerical modelling, empirical calculations of residual stresses, laboratory measurements of compression wave (ultrasonic) velocities on intact rock cores, in-situ primary stress measurements as well as site geological model were integrated to evaluate the use of seismic tomography for identifying possible in-situ stress increases around the excavation.A detailed calibration modelling was carried out based on the site seismic tomography measurements and during the large-scale modelling. It was observed that the increasing Vp is directly related to simulated increasing directional loadings on the rock mass. Using a measured wave raypath it was possible to check the different in-situ stress parametrizations which resulted in the best approximation to the measured Vp values.It was concluded that the rock mass under investigation to extend the repository must have higher in-situ stress values than the area of the constructed deposition chambers nearby. The results of this research indicated that seismic tomography is a useful tool for determining relative stress around and within the vicinity of underground excavation.

A theoretical approach to the residual stress assessment based on thermal field evaluation in laser beam welding

Residual stresses are one of the major issues in welded parts, since they could be detrimental to the integrity of components and structure. Their determination is rather complex and could be an arduous task, both when it is based on experimental methods and on numerical simulations. The proposed work presents a theoretical approach to the prediction of the longitudinal residual stress distribution, based on a parameterized multi-source model for thermal field simulation in laser welding previously introduced. Reference is made to the case of “keyhole” full penetration welding mode obtained by CO2 laser beam single pass on butt-positioned AISI 304L plates. The resolution of the thermal field allows the analytical calculation of the distribution of the longitudinal residual stresses in two ways: one makes use of a simplified formulation of the distribution well-known in the literature; a second modality makes use of a procedure for residual stress generation, which is based on a combined processing of thermal profiles and the corresponding heating–cooling cycles calculated in single points as their distance from the welding axis varies, and provides a complete characterization of the distribution of longitudinal residual tensile stresses. After the introduction of thermal field modeling, both the proposed residual stress calculation procedures are detailed, applied to the analyzed case, and validated, highlighting the differences in the approaches and results.

Rapid calculation of part scale residual stresses in powder bed additive manufacturing

Numerical modelling of thermo-mechanical residual stresses for laser powder bed fusion is complex and computationally intensive. A novel analytical model is presented here that can compute the residual stress distributions through a printed part and the baseplate quickly and reliably using phenomenological modelling. The peak residual stress for each deposited layer, needed in the model, is computed using scaling analysis. The computed residual stress distributions are tested with the corresponding independent experimentally measured and numerically computed results. The analytically calculated residual stress distributions are shown to be in good agreement with the corresponding independent results. The analytical model is shown to be 10,000 times faster than the numerical models.

Evaluation of Phase Transformation Strain and Its Influence on Residual Stress Generation in Laser Welded Ti–6Al–4V Alloy

Abstract The assessment of welding-induced residual stress is always of significant interest due to its adverse effect on the structural stability and mechanical performance of the welded structure. Incorporation of intricate phenomena, in particular, thermal gradient, phase development, volumetric dilation, and phase transformation strain during FE modelling, not only acts as a reliable method for residual stress calculation but also serves as a directive to reduce tensile residual stress in a weldment which is sensitive to the selection of materials. In order to investigate the same for continuous and pulse laser-welded Ti–6Al–4V alloy, the sequentially coupled thermal–metallurgical–mechanical models are established. The internal state-dependent variables (SDVs) are implemented to capture the growth of phase evolved during diffusionless β → α′ transformation using Koistinen–Marburger (K–M) theory in the cooling cycle. The role played by a phase transformation induced strain on the generation of residual stress is systematically investigated. The volumetric dilation and associated phase fraction form the basis for the estimation of phase transformation strain in the present study. The accomplishment of highest martensitic fraction (∼95%) produced a phase transformation strain of 7.95 × 10−3 in pulse mode of operation. As a result, reversal of residual stress from tensile to compressive is perceived for pulse laser-welded specimen. Similarly, a sign of enriched martensitic transformation is noticed that puts the weld surface into a compression state and mitigates the overall tensile residual stress. The assumption of diffusional phase transformation during heating cycle and non-diffusional transformation during cooling phase in laser welding is more appropriate to predict the residual stress using thermal–metallurgical–mechanical model.

Calculation of Residual Stress in Ships by the Method of the Fresnel Approximation

Predictive maintenance techniques are developed to help determine the condition of in-service equipment in order to predict when maintenance should be performed. There is a need for cost-performance effective approaches and methods for predictive maintenance that can make non-destructive on-site measurements to predict residual stress-induced critical faults in large metal structures, such as ships. In this study, an optical method based on the calculation of the non-destructive surface magnetic permeability coefficient is proposed for monitoring the residual stress distribution in AISI4040 and DUPLEX materials. In our proposed new method for determining theoretically the residual stress at the joint site of large plates in ships, the Lorentz-Drude model and the Fresnel approximation were used. Our results show that the new optical technique proposed in this study is sufficient and thriving for the determination of residual stresses in large metal structures.

The surface residual stress of monocrystalline silicon in ultrasonic vibration–assisted diamond wire sawing

Monocrystalline silicon wafer is the most important raw material in chip manufacturing; wire sawing is the most common processing method of monocrystalline silicon wafer. The residual stress generated by cutting affects the subsequent polishing costs directly, as well as the fracture strength and mechanical integrity of the monocrystalline silicon wafer, thus affecting the service performance. In this paper, the generation mechanism of residual stress was analyzed based on diamond wire sawing technology. Then, based on Drucker-Prager (D-P) plastic constitutive model, the magnitude and distribution of residual stress of monocrystalline silicon chip under different process parameters were simulated by ABAQUS simulation software. Finally, the experiment of ultrasonic vibration–assisted diamond wire saw cutting monocrystalline silicon was conducted, and the residual stress of monocrystalline silicon chips were detected by blind hole method. During the detection, the strain values before and after drilling in three directions of monocrystalline silicon chips were measured by strain gauge rosette, and then the residual stress values were determined according to the strain values and the residual stress calculation theory. The experimental results showed that residual compressive stress remains on the surface of silicon wafer in both conventional wire sawing and ultrasonic vibration–assisted wire sawing. The residual compressive stress increases with the increase of the axial speed of wire saw, decreases with the increase of the wire saw feed speed, and fluctuates with the increase of the workpiece rotation speed. The residual compressive stress on the surface of the silicon wafer by ultrasonic vibration–assisted wire sawing is larger than that by conventional wire sawing. The simulation and experimental results have the same trend, which verifies the validity of the finite element model in this paper and provides theoretical support for the subsequent processing of single crystal silicon.