Vibratory Stress Relief Research Articles

Effects of TVSR process on the dimensional stability and residual stress of 7075 aluminum alloy parts

Abstract Residual stress generated during the blank forming and machining process significantly influences the dimensional stability of the mechanical parts. The equivalent bending stiffness and thermal vibration stress relief (TVSR) are two factors that affect the deformation of thin-walled workpiece. To increase the machining accuracy, on the one hand, increase the equivalent bending stiffness in manufacturing, and on the other hand, usually conduct the stress relief process to reduce the residual stress in manufacturing. In the present study, morphology optimization and TVSR process are conducted on a thin-walled part Specimen B of 7075 aluminum alloy to control the residual stress and machining deformation before finish machining. As a contrast, Specimen A is machined in one step. The deformations vary with time of Specimen A and B are measured. The corresponding finite element model is built to further study the stress and distortion during the machining process. Results showed that (1) deformation decreased with the increase of equivalent bending stiffness, compared with Specimen A, the maximum deformation of Specimen B decreased by 58.28%. (2) The final maximum deformation of Specimen B can be reduced by 38.33% by topology reinforcement to improve the equivalent stiffness and TVSR to reduce the residual stress.

Effects of segmented thermal-vibration stress relief process on residual stresses, mechanical properties and microstructures of large 2219 Al alloy rings

Large 2219 Al-Cu alloy transition rings are extensively employed in propellant tanks of heavy launch vehicles. These rings have a diameter exceeding 5 m or even reaching 10 m, with a less than 2% thickness-to-radius ratio, and low stiffness which can cause machining deformation due to the residual stress. Thus, residual stress relief of these rings is necessary in their extreme manufacture. A novel effective method is thermal-vibration stress relief (TVSR), which integrates the conventional thermal stress relief (TSR) and vibratory stress relief (VSR); however, the existing TVSR equipment cannot meet the requirements of large rings, and the underlying mechanisms of TVSR remain unclear and a quantitative interpretation is still lacking. Therefore, a segmented TVSR (STVSR) process suitable for large rings was proposed and the corresponding experiment was carried out with a self-made STVSR experiment platform. Then this study investigated the evolution and distribution laws of the residual stresses, tensile properties, Vickers hardness, dislocations, precipitated phases and metallography during STVSR. Based on the experimental results, multi-scale mechanics theory and strengthening mechanisms were applied to quantitatively reveal the underlying mechanisms of residual stress relief by STVSR. The results showed that the circumferential and axial residual stress relief rates can reach 44.43% and 45.14% after STVSR, respectively. The residual stress relief after STVSR is attributed to the dynamic evolution of dislocations and precipitated phases in the material. The improvement of mechanical properties mainly depends on the precipitated phases and is also affected by the residual stress. The findings confirm the significant effects of STVSR on metal plasticity and provide valuable insight into the underlying mechanisms of TVSR.

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%.

Application of vibration stress relief in CFETR vacuum vessel welding

Several welding methods are used in the manufacturing of the CFETR vacuum vessel. These welding methods will inevitably lead to the problems of welding residual stress and welding distortion. Relieving welding residual stress is one of the important works in CFETR vacuum vessel welding and vibration stress relief (VSR) is one of the methods to relief the residual stress in the welding of the CFETR vacuum vessel. In this paper, the vacuum vessel PS3 segment is selected as the research object, and the VSR technology such as excitation point and support regions, excitation force and excitation frequency can be obtained through software simulation combined with the actual situation, which provides technical guidance for improving the effect of residual stress relieving.

Residual stresses in the aluminium alloy 2014A subject to PAG quenching and vibratory stress relief

Generic hollow pump bodies made from aluminium alloy 2014A forgings have been solution heat treated and quenched into either cold water or polyalkylene glycol (PAG) solutions. An industry standard PAG type synthetic quenchant was evaluated, and the influence of two concentrations of the PAG solution on residual stress in the pump bodies was characterised, using neutron and X-ray diffraction. These residual stresses were then compared to those resulting after a pump in the as quenched condition was subject to a widely known but controversial commercial vibratory stress relieving procedure. The use of neutron diffraction allowed the through thickness residual stresses to be evaluated in the pumps. Results demonstrate that PAG quenching is highly effective at significantly reducing residual stress when compared to cold water quenching, but the impact is non uniform and cannot be simply quantified. In this investigation, we prove the effect of vibratory stress relief is negligible, and much less than that achieved by PAG quenching.

Influence of the Nonlinear Stiffness Parameter of the Vibratory Stress Relief Device on Strong Nonlinear Superharmonic Resonance

Nonlinear superharmonic vibratory stress relief (VSR) is an effective way to solve the resonance problem of a high stiffness workpiece. However, strong nonlinear factors are present, and superharmonic resonance is relatively complicated when the entire device is a strongly nonlinear system. Choosing the best nonlinear stiffness parameter of the spring to allow the superharmonic resonance to generate a sufficient amplitude and sufficient dynamic stress becomes difficult. To solve this problem, it is necessary to explore the effect of the stiffness parameter on the system resonance: First, the nonlinear vibration situation of the VSR device is analysed, and the effect of the stiffness parameter on the vibration characteristics is explored under the action of the strong nonlinear system. Then, a simulated vibration table is used to verify the rule that the stiffness parameters affect the superharmonic resonance. It was shown that strong nonlinear theory provides a theoretical basis for simulating vibration table experiments, and the relationship between the spring stiffness parameter and amplitude satisfies a certain relationship, which provides a useful reference for the application and research of the VSR device for nonlinear superharmonic resonance.

Experimental and simulation investigation on thermal-vibratory stress relief process for 7075 aluminium alloy

Residual stresses evidently affect the strength, fatigue property and machining deformation of the mechanical components. Therefore, stress relief processes are extensively applied in the manufacturing to enhance the mechanical properties of products. In this study, seven 7075 aluminium alloy specimens are treated by thermal- vibratory stress relief (TVSR), thermal stress relief (TSR), and vibratory stress relief (VSR). Finite element (FE) models considering the stress relaxation effects and transient periodic vibration loads are proposed to simulate the TVSR, TSR and VSR process. The residual stresses before and after the processes are measured and compared, and the effectiveness of the FE models is validated. Scanning electron microscope (SEM) and transmission electron microscope (TEM) are used to observe the microstructure and crystal dislocation, respectively. Results show that TVSR can evidently reduce the residual stress in aluminium alloy, and the stress relief rate of TVSR for the peak stress are 20.43% and 38.56% higher than that of TSR and VSR, respectively. It also found that TVSR has no obvious influence on the grain size, but evidently increase the dislocation density. Eventually, the stress relief mechanism of TVSR is analyzed and summarized.

Residual stress relief of welded aluminum alloy plate using ultrasonic vibration

Ultrasonic vibratory stress relief (UVSR) is a novel method for residual stress relieving of metal parts. In this paper, the UVSR method was applied to treat a random-sized plate, which is not designed to match with the resonant frequency of the ultrasonic transducer. The UVSR system includes an ultrasonic generator, a 20 kHz ultrasonic transducer and specially designed fixtures to exert ultrasonic vibration to the treated parts. Based on the experimental results, the average stress relief ratio reached 53% and the final residual stress distribution interval was reduced by 57. The vibratory stress introduced by the ultrasonic vibration was obtained accurately by matching the FE model with the measured vibration amplitude distribution. It is found that local yield stress, instead of macroscopic yield stress, should be used as the threshold of residual stress relieving. Moreover, if the local yield stress of a material is constant, the local yield stress of 6082 aluminum alloy is reduced by at least 27% during the UVSR. Finally, it is found that the residual stress relief rate in one direction is proportional to the vibratory stress introduced in that direction.

Evolution of internal friction in low-carbon steel during vibratory stress relief

Vibratory stress relief has been reported to induce crystal lattice movements, which are forms of the internal friction of a material. In this study, low-carbon steel specimens were vibrated to analyze the evolutions of their internal frictions and stress-relieving effects. Specific vibration frequencies were found to produce relatively higher internal frictions and stress-relief ratios. For a fixed vibration frequency, higher vibrational amplitudes were found to induce higher internal frictions. When vibrated for the same amount of time but at varying amplitudes, the internal frictions of the specimens either decreased with time (which indicates the effects of stress relief) or increased with time and fracturing the specimen owing to fatigue. These results indicate that the increasing of internal friction could serve as an index for fatigue crack nucleation in low-carbon steel.

Effect of laser shock processing on mechanical properties of Ti-45.5Al-2Cr-2Nb-0.15B alloy

In order to study the effect of laser shock processing (LSP) on mechanical properties of Ti-45.5Al-2Cr-2Nb-0.15B alloy. The Ti-45.5Al-2Cr-2Nb-0.15B alloy samples, after the treatment of vibration stress relief, were LSP treated by a high energy nanosecond Nd:YAG laser. The surface micro-hardness, surface residual stress and surface roughness of samples prior & after the LSP treatment were tested by the micro-hardness tester, hole-drilling strain method and the roughness tester, respectively. The experiment results show that after the treatment of LSP, resulting in a certain residual compressive stress on the surface of the sample. When the laser energy is increased to 7 J, the surface residual stress is increased from 0 MPa to −311 MPa, the surface micro-hardness is increased from 311 HV to 366 HV, and the surface roughness is increased from 43 μm to 72 μm. With the treatment of LSP, the mechanical properties of Ti-45.5Al-2Cr-2Nb-0.15B alloy is improved greatly.

Welding residual stress reduction assessment in steel rings via the spectral harmonic vibration aging test

The generation of welding residual stress easily causes fatigue cracks in the interior of the structure where the welding residual stress is high. It finally causes the fatigue fracture under the combined action of external load and internal stress, resulting in failure of welded structural parts. It has the fatigue crack and fracture failure during the use of the radial engineering steel ring. In view of this phenomenon, this paper proposes a spectrum aging test analysis of steel rings using spectral harmonic vibration stress relief system. Through the statistical analysis of the test data, the results show that after the vibration aging treatment, the transverse and longitudinal welding residual stresses in the steel ring’s weld seam have a large downward trend as a whole, and the residual stress reduction rate of each test point is about 25%. This study provides a reference for the application of vibration aging technology to steel ring weldments.

Quantification of CTOD fracture toughness in welded joints to evaluate the efficacy of vibration stress relief compared to thermal stress relief

Resonant vibration residual stress relief (R-VSR) is an alternative method to post-weld heat treatments (PWHT) which is said to lead to less distortion and lower costs. The method of superposition of cyclic stresses and residual stresses, which can lead to localized yielding of the material, dislocation movement and subsequent stress relief. This article aims at investigating the efficiency of resonant vibration in the relief of residual stresses in welded joints of HSLA Domex700 steel sheets. Mechanical stress relief was compared to a common PWHT, and stress levels were then quantified through X-ray diffraction. Samples were also characterized by CTOD fracture toughness tests, fractographic analysis and tensile tests. Results indicate that the mechanical method was significantly less effective in relieving stresses in comparison with the PWHT, but led to apparent improvements in fracture toughness and in tensile tests. FWHM values indicated significant distortion for PWHT and less distortion for R-VSR.

Vibratory Stress Relief and Vibratory Weld Conditioning of Flux cored arc welded CA6NM steel

ASTM A743 CA6NM steel is used in the manufacturing of hydraulic turbines components. Multipass welding is commonly used for their fabrication or repairing. In this work, two different vibratory welding procedures were studied: vibration applied during welding (VWC) and vibration applied after welding (VSR). Results have shown that in both conditions, CA6NM steel presented a martensitic microstructure, in which the VSR welded joint presented column-shaped packets and fine martensite delineating the individual beads, while VWC joint presented grain refinement. Heat affected zones (HAZ) presented δ-phase in small amounts for both conditions in the regions which reached higher temperatures. VSR and VWC conditions presented similar behavior in terms of hardness, HAZ hardness values being close to those of the weld metal, except for the root regions, where higher values were obtained. Charpy-V results showed that HAZs presented higher impact values than those of the weld metal. The low impact values of the weld metal were attributed to presence of inclusions from the welding electrode.

Investigation of residual stress relaxation on Cr12MoV steel under high-frequency cyclic loading

High frequency vibratory stress relief (VSR) is a procedure to reduce the residual stresses by means of high frequency cyclic dynamic stress. Cyclic loading, or cyclic dynamic stress, imposed on the workpieces during the high frequency VSR affects the reduction of the residual stresses. In this study, the high frequency VSR was carried out on the Cr12MoV steel quenched specimens. And the residual stresses on the Cr12MoV steel surface before and after the high frequency VSR were studied by the hole-drilling method. The results show that the residual stresses can be effectively reduced by the high frequency VSR. Moreover, increasing the high frequency vibration frequency and the high frequency vibration amplitude can improve the effect of the high frequency VSR.

Experimental Investigation of Vibration Stress Relief of A106 Steel Pipe T-Welded Fittings

This research examines the use of vibratory treatments to reduce residual stresses in small welded parts. In this experimental investigation, a post weld vibration treatment was applied to T- A106 steel pipe fitting specimens to study the effect of the treatment on the residual stress and the hardness of the material. The vibratory stress relief treatment was carried out at different vibration frequency. The results have demonstrated that post-weld vibratory stress relief of small size fittings is possible and residual stress may be relieved, and the treatment may be an alternative method for heat treatment especially when unchange in dimensions and material stability are required.

Definition of energy efficient law of mechanical impact in vibratory stress relief of metal parts

The study is based on the method of vibratory stress relief, which is used to reduce the residual stresses in cast and welded parts, and is an alternative to thermal deformation methods, because it is unpretentious to the mass, shape and dimensions of the part. Vibratory stress relief is usually carried out using unbalance electromechanical systems, which are simple in design of the power section and control system. In such systems, processing occurs simultaneously at only one resonant frequency. The workpiece, as a rule, is characterized by several resonant frequencies that have a tendency to shift to the low-frequency region during the implementation of the vibration effect. The technological process of sequential processing at each variable resonant frequency is rather time-consuming and not efficient in terms of the cost of electrical energy. In order to reduce the cost of time and energy, this study proposes the use of the most advanced processing methods at several resonant frequencies. Based on the algorithms of sequential vibratory stress relief at several resonant frequencies of the part and their changes towards low ones, it was proposed to carry out processing by a polyharmonic perturbing force in a limited frequency band. This effect has a bandwidth that contains all the possible frequencies of the part where vibratory stress relief occurs. Such an effect can be realized with the help of an electrodynamic linear motor as an executive body. The advantage of an electrodynamic linear motor is the proportionality of the generated force to the current supplied to the moving conductor and its repetition in form. By means of mathematical modeling for the selected example, it was found that narrowing the frequency range in the low-frequency region by 5 times reduces energy costs by more than 4,000 times as compared with the broadband law of mechanical action on a part. A theoretically determined energy-efficient law can be software-implemented in control systems for electrodynamic linear motors that implement vibratory stress relief

Residual Stress Relief for 2219 Aluminum Alloy Weldments: A Comparative Study on Three Stress Relief Methods

Thermal stress relief (TSR), vibration stress relief (VSR), and thermal and vibratory Stress relief (TVSR) have all been proven to be effective for residual stress relief. So far, no comparison has been made between the effects on residual stress relief of these three stress release methods. In this study, twelve 2219 aluminum alloy welding samples were divided into four groups. One of the groups is used as a reference without any stress relief treatment. The other three groups were processed by TSR, VSR, and TVSR, respectively. The residual stresses of depths of 0–1.2 mm are measured. Results show that small and uniform stresses are observed in the 2219 aluminum alloy welding samples after TSR, VSR, and TVSR treatment. TSR treatment decreased the peak residual stress much more than VSR and TVSR treatment. The maximum reduction of the peak residual stress is 50.8% (210 °C) in the transversal direction and 42.02% (185 °C) in the longitudinal direction after TSR treatment with the temperature range 140 °C to 210 °C. In terms of residual stress homogenization, although the TSR treatment has an advantage perpendicular to the weld direction, the effect parallel to the weld direction is not ideal. The TVSR has a good effect in both directions.

The online monitoring method research of laser shock processing based on plasma acoustic wave signal energy

Aiming at the phenomenon of plasma acoustic wave during laser shock processing, the online monitoring method of laser shock processing based on plasma acoustic wave signal energy is proposed. The TC4 titanium alloy samples, after the vibration stress relief treatment, were treated by a Nd:YAG laser system with a wavelength of 1064nm, a pulse width of 12–18 ns, and a single pulse energy of 0–7 J. The plasma acoustic wave in air is sampled, stored, digitally filtered, and analyzed by the laser shock processing online monitoring system during laser shock processing. Then the system gets the plasma acoustic wave signal energy. The surface residual stress of material after the treatment of laser shock processing were measured by a Photo-LXRD X-ray diffraction device. The experimental results show that the residual compressive stress is generated on the surface of material after laser shock processing. Both the surface residual stress of the material and the plasma acoustic wave signal energy are increased as the laser pulse energy increases from 3J to 7J, and their growth trend is consistent. Finally, the empirical formula between the surface residual compressive stress of the material and the plasma acoustic wave signal energy is obtained by polynomial fitting, which will provides a theoretical basis for the development of laser shock processing online monitoring technology.

The influences of the cyclic force magnitude and frequency on the effectiveness of the vibratory stress relief process on a butt welded connection

Welding residual stresses are considered as significant factors for the reduction of fatigue life and load bearing of welded structures. In this article, characterization of a low-temperature stress-relief method called vibratory stress relief process was investigated. In this regard, welding of a butt joint of two steel plates was simulated and induced welding residual stresses were calculated. An experimental residual stress measurement was conducted to verify the numerical results. It was established that the simulated residual stresses are in good agreement with the measured results obtained from the hole drilling strain gauge measurements. In the following, the vibratory stress relief process of the welded joint was simulated using finite element method (FEM). It was observed that by controlling the process parameters, a notable reduction in the residual stress is achievable. Effects of magnitude and frequency of the cyclic force on the effectiveness of the stress relief process were studied. The results indicated that by increasing the applied load frequency up to 95% of the natural frequency, the longitudinal residual stress decreased more than 80%. Also, it has been shown that by increasing the force magnitude, the welding residual stresses were reduced drastically.

Effect of Vibration Stress Relief on the Shape Stability of Aluminum Alloy 7075 Thin-Walled Parts

Aluminum alloy 7075 is one of the materials widely used in the manufacture of structural components used by aviation industries. High precision is required in producing the shapes of such components due to shape stability and dimensional accuracy being difficult to maintain throughout the different stages of manufacturing. In this work, an experimental study of the effect of VSR (Vibratory Stress Relief) on the deformation and residual stresses of aluminum alloy 7075 thin-walled components is presented. It was concluded that VSR improved the shape and size stability of the material to a significant level by relieving induced residual stresses in the thin-walled parts. Finally, more uniform residual stress distribution was obtained after the VSR treatment, compared to before the VSR treatment. This proved that VSR has a significant influence on improving the shape stability of the thin-walled aluminum alloy 7075 components.