Elimination Of Residual Stress Research Articles

Deformation behavior and stress relaxation modeling of Cu–3Ti alloy prepared by a novel rolling process with the shortened passes

This study explores the effects of hot rolling with a shortened process on the microstructure and properties of Cu–3Ti alloy compared to the traditional multi-pass forming, and the finite element simulation was used to predict the experimental results. At the same time, the residual stress elimination model was used to provide prediction and reference for the relaxation of residual stress during the alloy annealing process. The residual stress of hot rolled samples through the shortened passes is reduced by an average of about 6.7 % after the appropriate annealing treatment, and accompanied by an obvious increase in the yield and tensile strengths compared to that of the traditional multi-pass forming. At the same time, this hot rolled sample by 90 % reduction with 9 passes contains a 45.7 % proportion of high-angle grain boundaries due to the occurrence of extensive dynamic recrystallization, which remains a good consistence with the higher strength under this condition.

Evolution mechanism of interfacial microstructure and regulation of mechanical properties of laser-arc hybrid weld-brazing aluminum/steel joints under different post-welding heat-treatment temperatures

Control of the interfacial microstructures and mechanical properties of aluminum/steel joints after welding is crucial to prolonging the service lives of such structures. In this study, the influence of post-welding heat treatment (PWHT) on aluminum/steel laser-arc weld-brazing joints was investigated, with particular focus on the evolution mechanisms of the interfacial microstructures and regulation of the mechanical properties. Transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) results confirmed the presence of the monoclinic Fe4Al13 and hexagonal Al8Fe2Si phases at the aluminum/steel interface. Upon increasing the heat-treatment temperature, micro-characteristics of the intermetallic compound (IMC) passed through three different stages (weak elemental diffusion–reaction–drastic change) depending on the temperature employed; these stages differed from the PWHT phenomenon observed for the aluminum/steel solid-state welded joints. EBSD analyses revealed decreases in the grain size and textural strength of the IMC layer following PWHT at 180 °C/1 h, while the Fe4Al13 phase gradually transformed into Al8Fe2Si phase during PWHT at 520 °C/1 h, ultimately leading to an increase in the grain size and a higher textural strength. Additionally, PWHT effectively eliminated the residual tensile stress in aluminum/steel joints and improved the softening of the heat-affected zone (HAZ). Upon PWHT at 180 °C/1 h, the synergistic effects of the elimination of residual stress, an enhanced softening in the HAZ, and changes in the IMC layer, led to improved joint properties. Furthermore, the maximum tensile strengths of the joints with and without reinforcement increased to 221.9 MPa (from 209.8 MPa) and 165.3 MPa (from 148.1 MPa), respectively.

Regulate the microstructure, tensile properties and fatigue crack growth behavior of an Al–Zn–Mg–Cu alloys fabricated by laser powder bed fusion via post-heat treatment

An Al–Zn–Mg–Cu–Si–Zr–Er alloy was fabricated by laser powder bed fusion technology. A unique cellular structure consisting of α-Al, Mg2Si, and Al2CuMg phases was observed in both as-printed (AP) and direct aging (DA) alloys. Direct aging treatment at 150 °C × 4 h can improve the yield strength and hardness of the alloy, and precipitation strengthening and fine grain strengthening are dominant mechanisms. The strength of the regression re-aging (RRA) heat treated alloy decreased, while the elongation was obviously improved, and the grain boundary was continuous without precipitates free zones. DA could not significantly hinder the fatigue crack growth rate of the as-printed alloy, but the improvement of plasticity, elimination of residual stress, and the effect of precipitates in RRA alloy extend the life of the fatigue crack growth stage, thereby improving the overall fatigue life of the alloy from 1.17 × 105 cycles to 3.93 × 106 cycles.

Effect of excitation vibration on mechanical property and stress corrosion resistance of cast steel

Cast steel parts can realize rapid prototyping effectively, which is suitable for complex structural design. However, due to the large residual stress, the problem of mechanical property degradation is more obvious. In order to solve this problem, a high temperature excitation vibration treatment scheme is proposed in this paper. By applying different excitation frequencies and impact forces, the effects of mechanical properties and stress corrosion properties are studied and verified. Based on the finite element software ANSYS, the modal shape and resonant frequency of the cast steel parts are obtained, and verified by the sweep frequency module in the excitation vibration system. According to the characteristics of modal shape, five typical detection paths are set, and stress sensors are arranged every 200 mm. In order to obtain the specific effects of excitation frequency and impact force amplitude on mechanical properties, nine parts samples were prepared on the same production line according to the matching requirements of test parameters. In addition, the main external parameters that remain unchanged during vibration excitation are set as initial 750 ℃ and vibration excitation time of 60 s, which can fully affect the effect of austenite transformation. Keeping the synchronization of test parameters in different samples, the distribution rules of residual stress under different excitation frequencies and forces are obtained and analyzed. In the aspect of mechanical properties, the microstructure, hardness, yield strength and tensile strength of the specimens subjected to vibration were compared and analyzed. In the aspect of stress corrosion performance research, stress corrosion cracking test was carried out in weak acid environment to obtain the tensile stress curve and fracture morphology of the specimen. The results show that the excitation vibration at high temperature can effectively eliminate the residual stress of cast steel parts, but the increase of excitation frequency does not correspond to the effect of residual stress elimination. When the exciting force exceeds a certain value, the stress relief effect cannot be further improved. Excitation vibration can reduce the internal hardness of cast steel parts to a certain extent, and improve the yield strength and tensile strength. At the same time, it has a positive role in promoting the improvement of stress corrosion resistance.

Welding Residual Stress Elimination Technique in the Top Chord of Main Truss of Steel Truss Bridge

The large-amplitude fluctuations of ultrasound in high-energy ultrasonic stress relieving cause the crystal grains or lattices in the high residual stress zone to vibrate or creep alternately. This triggers secondary effects such as ultrasonic softening and dislocation movement. The sound field also produces periodic shock waves or intermittent shock waves, which form local pressure gradients at the wave front. These pressure gradients cause local heating of the grain boundary, accelerating material softening and promoting slip between grains, ultimately resulting in residual stress elimination. This technique was applied to detect the welding residual stress of the upper chord of the main truss of Sanguantang Bridge by using an ultrasonic stress meter. After the measurement, it was found that the welding residual stress in some areas was too large, and the welding residual stress needed to be eliminated. The welding seam was re-inspected after the residual stress relief operation was completed. The test results showed a maximum reduction rate of 63.91% and an average overall reduction rate ranging from 24.52% to 37.23%. The reduction effect is more significant in areas with higher welding residual stress.

Research on the Thermal Behavior of Surface Texture on Laser Cladding Layer of Mold Steel

To extend the service life of mold steel and reduce the residual stresses generated during laser cladding to reduce defects such as surface cracks, this paper conducts a simulation study in terms of optimizing the laser cladding process parameters and pre-setting the surface texture. Firstly, using residual stress as an indicator, a three-factor, three-level orthogonal experiment was conducted using ANSYS on three factors: laser power, scanning speed, and spot radius, and then the experimental results were subjected to signal-to-noise ratio and extreme difference analysis to obtain the optimum process parameters: laser power of 800 W, spot radius of 1 mm and scanning speed of 20 mm/s. Subsequently, the mould steel was pre-textured under the optimum process parameters and the temperature and stress fields of the clad layers were compared with those without pre-texturing. The results show that the average residual stress in the pre-textured clad layer is 149 MPa, which is 58.56% lower than the average residual stress in the unpre-textured clad layer, which is consistent with the experimental results and verifies the feasibility of pre-texturing in the elimination of residual stress.

Effect of freeze-thaw cycling on the mechanical properties of continuous carbon fiber-reinforced polyamide 6 composites

This paper deals with the effects of different freeze-thaw cycling environments on the mechanical properties, dimensional stability, and water absorption behaviors of continuous carbon fiber reinforced polyamide 6 composites (CF/PA6). In a nominally dry state, freeze-thaw (FT) exposure can slightly increase the mechanical properties due to the elimination of residual stress. However, FT exposure in a water immersion environment causes a linear decrease in transverse tensile properties and flexural properties and an exponential decrease exposure in water immersion environment. This difference in degradation rate can be attributed to the varying water content, and the relationship between retention rate of mechanical properties and FT cycles was further developed to predict its long-term aging performance. In addition, water absorption behaviors, dimensional measurement, and micro-characterization were also applied to analyze the mechanism of mechanical properties degradation.

On Defect Minimization Caused by Oxide Phase Formation in Laser Powder Bed Fusion

The article is devoted to the compressive review of the defects observed in the products of the machinery usage made mainly of anti-corrosion steels of the martensite-austenite group, difficult to process materials such as pure titanium, nickel, and their alloys, super and high entropy alloys and triple fusions produced by laser additive manufacturing, particularly the laser powder bed fusion. Studies were conducted on the structural defects observed in such products to improve their quality in the context of residual stress elimination, porosity reduction, and surface roughness improvement. Electrophysical and electrochemical treatment methods of removing oxide phase formation during melting and remelting of deposed tracks in layers are considered (such as ultrasound, plasma, laser, spark treatment, induction cleaning, redox annealing, gas–flame, plasma–beam, plasma–spark treatment). Types of pollution (physical and chemical) and cleaning methods, particularly plasma-based methods for oxide phase removing, are classified. A compressive comparison of low- and high-pressure plasma sources is provided. Special attention is focused on the atmospheric plasma sources based on a dielectric barrier and other discharges as a part of a production setup that presents the critical value of the conducted review in the context of the novelty for transition to the sixth technology paradigm associated with the Kondratieff’s waves.

Effect of Heat Treatment on Residual Stress of Cold Sprayed Nickel-based Superalloys.

Residual stress formation during cold spraying process may result in deteriorative effects on the performance of coating materials. The objective of this investigation is to characterize residual stress built-up in two well-known nickel-based superalloys (Inconel 625 and Inconel 718) deposited using cold spraying technique. To this end, the residual stress was precisely measured using x-ray diffraction method. Here, residual stress in the subsurface regions was only studied because the surface properties may alter during sample preparation. The average residual stress was slightly higher in Inconel 625 compared to the Inconel 718 sample. Heat treatment at 800 °C helped in the reduction of porosities which exerted tensile stress in subsurface regions of both coatings. Stresses with opposite signs could cancel each other and result in reduction of residual stress after heat treatment. However, the recovery of residual stress was higher for Inconel 718 coating. In the next step as-sprayed and heat-treated coating samples were subjected to microindentation test to measure their hardness and study the crack formation in the samples. The as-sprayed Inconel 625 exhibited higher hardness than Inconel 718, but the hardness of Inconel 625 decreased more drastically after heat treatment. While the cracks were formed on both as-sprayed samples around indents, no cracks were found in the heat-treated samples. The results from this study will contribute to better understanding the performance of cold spray deposited superalloys under service conditions and the effect of stress relaxation heat treatment on elimination of residual stress.

Enhanced thermoelectric properties from pore design via adjustment and elimination of residual stresses for Yb0.2(CoSb2.875Te0.125)4

Enhanced thermoelectric properties from pore design via adjustment and elimination of residual stresses for Yb0.2(CoSb2.875Te0.125)4

Numerical simulation of the effect of ultrasonic impact treatment on welding residual stress

Ultrasonic impact treatment (UIT) is an effective method that has been widely applied in welding structure to improve the fatigue properties of materials. It combines mechanical impact and ultrasonic vibration to produce plastic deformation on the weld joints surface, which introduces beneficial compressive residual stress distribution. To evaluate the effect of UIT technology on alleviating the residual stress of welded joints, a novel numerical analysis method based on the inherent strain theory is proposed to simulate the stress superposition of welding and subsequent UIT process of 304 stainless steel. Meanwhile, the experiment according to the process was carried out to verify the simulation of residual stress values before and after UIT. By the results, optimization of UIT application could effectively reduce the residual stress concentration after welding process. Residual tensile stress of welded joints after UIT is transformed into residual compressive stress. UIT formed a residual compressive stress layer with a thickness of about 0.13 mm on the plate. The numerical simulation results are consistent with the experimental results. The work in this paper could provide theoretical basis and technical support for the reasonable evaluation of the ultrasonic impact on residual stress elimination and mechanical properties improvement of welded joints.

Finite Element Simulation Analysis on Residual Stress Relief of 7075 Aluminum Alloy Ring

Vibration stress relief (VSR) and thermal stress relief (TSR) are important method to eliminate the residual stress of structural parts. The thermal vibratory stress relief (TVSR) is a new method to decrease and homogenize the residual stress. Based on the stress relaxation tests and the equivalent vibration equation of modal analysis, the creep constitutive model and the bilinear isotropic hardening plasticity material model (BISO) are combined to establish the numerical simulation model of TVSR of 7075 aluminum alloy ring part. The simulation results show that four different initial blank residual stress levels are obtained after quenching process, and the residual stress elimination and homogenization effect of TSR and TVSR is better than that of VSR. TVSR has a better effect on both residual stress elimination and homogenization, and the residual stress relief rate can reach more than 20%.

Effect of Pulsed Magnetic Field on the Residual Stress of Rolled Magnium Alloy AZ31 Sheet

A novel method of pulsed magnetic field (PMF) treatment was developed to eliminate the residual stress of rolled magnesium alloy AZ31 sheet in this study. The effect of PMF on residual stress of rolled AZ31 sheet was investigated and its mechanism was analyzed. The experimental results revealed that the pulse frequency had a significant impact on residual stress. After 10.0 Hz PMF treatment, the average and maximum reduction rates of residual stress along the rolled direction were 26.6% and 30.3%, respectively. It was found that the dislocation density and parallel dislocation in grains of the rolled sheet increased after it was treated by the pulsed magnetic field. The simulation results showed that the Lorentz force generated by the pulsed magnetic field can lead to basal slip, thereby resulting in local plastic deformation. Besides, the Joule heat produced during the PMF treatment was conducive to the elimination of residual stress.

Experimental study on the residual stress of the power spinning rod bushing with main technological parameters

Abstract In the course of plastic forming, the residual stress of the power spinning connecting rod bushing will be produced. The residual stress will influence the dimensional precision and leads to bushing fatigue failure. In view of the residual stress size and distribution and the elimination of residual stress. In this paper, a single factor test was carried out for the research object with the power spinning rod bushing of tin bronze (QSn7-0.2). This paper puts forward the X-ray diffraction method combine with electrolytic polishing method to measure different levels of residual stress and carry on the analysis to the experimental result. The influences of the main parameters (thinning ratio, the first wheel of reduction, feed rate, heat treatment temperature and holding time) on the residual stress were obtained. The results show that: after the power spinning, the surface of the connecting rod bushing is the residual compressive stress, the inner layer is the residual tensile stress, the residual stress at both ends of the bushing is greater than the residual stress in the middle part of the work. In a certain range, the surface residual stress of the connecting rod liner increases with the increase of the thinning ratio, and decreases with the increase of the feed ratio then increases, and decreases with the increase of the first wheel thinning. In a certain range of temperature, the connecting rod bushing after the strong spinning is treated by heat treatment, the surface residual stress will decrease with the increase of temperature, and the longer the holding time, the more obvious the effect of removing residual stress

Mechanical properties and microstructural evolution of TA15 Ti alloy processed by selective laser melting before and after annealing

Selective laser melting (SLM) is a promising additive manufacturing technique with growing acceptance in aerospace applications. In this work, a new aeronautical material of near-α Ti alloy (TA15) for SLM was firstly investigated and analyzed before and after annealing, mainly including mechanical properties, microstructural evolution. The distinctions between SLMed TA15 and wrought TA15 are also discussed in this study. Firstly, near full density TA15 samples (99.98%) were fabricated by SLM utilizing the optimized processing parameters. Then microstructures and textures are characterized and analyzed by optical microscope, X-ray diffractometer, scanning electron microscope and transmission electron microscope. Furthermore, mechanical properties of TA15 samples are measured via tensile and hardness test, considering the impacts of building direction. The results show that both the as-built and the annealed SLMed samples exhibit significantly weak textures and unconspicuous anisotropy of mechanical properties. It has been identified that αʹ martensite is dominant in the as-built microstructure thus contributing to ~1296 MPa in ultimate strength and ~398 HV in hardness which are 35% and 24% higher than those of wrought material. However, a low plasticity with ~7.6% of elongation at break was observed. After annealing, SLMed samples exhibited excellent comprehensive mechanical properties with 51% improvement at elongation through elimination of residual stress and precipitation of nanometer size β phase in the fine basket-weave structure.

Numerical simulation on residual stress eliminated by shot peening using SPH method

The residual stress in the vacuum vessel of future magnetic confinement nuclear fusion reactors should be eliminated either during the welding process or after the welding is completed. Shot peening is an effective method to eliminate welding residual stresses. In order to investigate the effect of shot peening on welding residual stress, a numerical simulation on eliminating the welding residual stress by shot peening using smoothed particle hydrodynamics (SPH) was performed. A model based on the SPH theory was established, the change of welding residual stress during the shot peening process was investigated. In addition, the change of welding residual stress before and after shot peening was studied. The effect of shot peening speed on residual stress was analyzed. The results demonstrated that the maximum residual stress changes continuously during shot peening. Moreover, shot peening can significantly improve the lateral and longitudinal residual stresses, but no obvious changes were found in the residual stresses along thickness direction. The shot peening speed affected the residual stress elimination effect, which provides guidance for the actual production process.

Прогнозна оцінка ефективності підвищення втомного опору елементів зварних конструкцій термообробкою

An analysis of influence on the magnitude of the limiting residual stresses of the cycle of welded joints is performed. An equation for determining the maximum boundary stresses of a cycle subjected to the treatment of a welded joint is obtained. The methodology for calculating the effectiveness of the complete elimination of residual stresses by heat treatment is applicable not only for the case when the output residual stresses in the welded joint reach the value of the material yield strength, but also for the case when these stresses do not exceed the value but above the limit value of the initial residual stresses, in which the maximum stresses in the zones of the weld hubs during cyclic loading reaches the value of the material yield strength.Dependences were obtained for determining the boundary stresses for local heat treatment of metal structures by locally lumped heat fluxes. It has been established that reducing the output level of residual weld stresses increases the boundary of endurance of joints joints. On the basis of the developed method of estimating the impact of residual weld stresses and their redistribution as a result of local heat treatment, the dependence of the limiting value of residual stresses on the coefficient of asymmetry of the external load cycle was investigated.The analysis of the obtained correlations and experimental data indicates that the local heat treatment leads to a significant increase in the boundary stresses and cyclic durability of the welded joints. The effectiveness of such a type of strengthening of the elements of welded structures depends on the mechanical characteristics of materials, parameters of external load, type of connections, etc. The greatest influence of local heat treatment is on the resistance of fatigue welded joints of constructions in conditions of an alternating load cycle.

Influence of post-weld heat treatment on microstructure and adhesion of Ti/Cu composite

ABSTRACTIt is well known that brittle interfacial intermetallics are typically present in laminated composites and degrade their mechanical performance. To investigate the relationship between intermetallics and mechanical properties, Ti/Cu-laminated composite plates prepared by explosive welding were studied with different heat treatments. A transition layer containing four zones of intermetallic phases, Cu4Ti, Cu4Ti3, CuTi, and CuTi2, was found at the interface between Ti and Cu after explosive welding. The intermetallics became thicker as the temperature of the heat treatment increased, especially for the CuTi phase. The sample treated at 473 K exhibited the highest bonding strength of 199.7 MPa, which was attributed to the elimination of residual stress during the welding and the diffusion of copper to improve interfacial bonding.

In a 21-2n deformed stainless steel influence of recovery temperature

We present the influence high heat treatment temperature of a nitrogen austenitic stainless steel, deform by cold compression, in 10 different percentages. The steel contains high chromium (19.25 %), nickel (1.5 %) and nitrogen (0.2 %). The typical applications for this alloy are automobile parts and special valves for his excellent mechanical properties and corrosion resistance. Produced by hot rolling, they were subjected homogenized treatment at 975 °C for 45 minutes. Subsequently, deformed, by cold compression. We get ten different deformations, from 3 % to 22 %. These samples then to a heat treatment at 750 °C for one, 2 and 4 hours respectively. To observe the microstructure all samples were metallographic study and measured also their Rockwell C hardness. The initial sample has an austenitic matrix with a small amount of precipitates with a 42 RC average hardness. The homogenized sample had a 39 RC hardness. The deformed samples increased their hardness with a maximum of 49 RC. The samples with the treatment, showed a lower hardness with longer time with high dispersion. The decreased of hardness is due to the elimination of residual stresses and precipitates increasing size.

Comparison of residual stress in relaxed and non-relaxed weldments of steel plates

In this study, two methods, X-ray diffraction (nondestructive) and hole-drilling (destructive) are applied to measure the residual stress of gas metal arc welded steel plate. Both non-relaxed and relaxed (local heating, furnace annealing and bead blasting) weldments are examined to understand the residual stress distributions before and after elimination of residual stresses. Results show that the heat affected zone of gas metal arc welding method is about 10 mm from the weld centerline. The local heating method is very effective in reducing the residual stress caused by the cold work of the original steel plate. The furnace annealing method reduces the residual stress to compressive but not uniformly distributed. The detrimental fluctuation of residual stress is successfully reduced and uniformly relaxed to be beneficially compressive in the bead blasting. Most importantly, X-ray diffraction shows more precise and better handling than hole-drilling method in terms of data error.