Papers by Keyword: Vibratory Stress Relief

Abstract: There are number of different methods and procedures in vibration analysis, where the natural frequencies of the specimen or the system are one of the key parameters. It is known that these frequencies can change under load, for example in response to pre-stressing, but the effect of residual stresses is less known. By developing a suitable method, natural frequencies can be used to predetermine residual stress, therefore this method can be used for example predicting whether it will cause deformation during machining of a part, whether it requires increased attention or how to set the parameters well for vibratory stress relief. The results can be significant cost and time savings, as well as the improvements of the quality. Natural frequency is the frequency of free vibration of an undamped linear vibration system, or in other words at which a system left alone will vibrate after excited by an external force [1]. Metal castings or welded structures may have several natural frequencies which appear as frequency bands or ranges on the measurement images. Based on these, to determine the natural frequency of a component or system, we need to excite a frequency as close as possible to the natural frequency for the resonance to occur. When the resonance is reached, the amplitude of the system is at its maximum, and the natural frequencies of the workpiece can be measured. Traditionally, sensors, usually accelerometers are used to measure the natural frequency. The continuous development of information technology has made it possible to replace these sensors with an acoustic diagnostic system. During this research, we have developed an acoustic diagnostic system and procedure, which can generate the acoustic measurement images. We have evaluated the measurement images in many ways, and many different types of components and materials (mostly iron alloys) were analyzed. In addition, the changes of natural frequencies show a similar pattern in the case of parts before treating with vibratory stress relief as for load tests.

Abstract: The assembling process of the flex lead of an accelerometer can bring in internal stress, which causes drift error and affects the precision of the accelerometer. The paper introduces a method using ultrasonic vibration to reduce the internal stress, discusses the theory of ultrasonic stress relief on fine wires, shows ultrasonic stress relief experimental apparatus which uses an optimized ultrasonic tool head to inflict ultrasonic vibration to fine wires. By introducing the displacements of the fine wire ends into ANSYS, changes of the internal stress of the fine wire can be obtained. The experiment studies the performance of ultrasonic vibration to fine wire internal stress and deals with the relationship between infliction time and results. The experiment results confirmed that by selecting the suitable experiment parameters, ultrasonic vibration is an effective way to internal stress relief, the internal stress decline as infliction time increase then stays.

Abstract: In this paper we investigated the influence of vibratory stress relieving technique, which is widely used for stress relaxation of weld and casting components/structure, on machining residual stresses in a ring-component of 12%Cr-steel. It was shown that the employed vibratory treatment, without significantly altering the microstructure, turned the surface layer from tension into compression but retained the compressive residual stresses in the subsurface. In comparison, a stress relieving heat treatment, included as a reference in the study, removed completely the surface tensile residual stresses and reduced the subsurface compressive residual stresses to a low level. Significant microstructural changes in the form of recrystallization also occurred in a thin surface layer of the machining affected zone after the heat treatment.

Abstract: In order to determining technological parameters and effective range of vibratory stress relief (VSR) treating for the radial steel gate structure, kinetic analysis was carried out according to the industrial standard. The natural frequency, vibration mode and the curves of amplitude-frequency were obtained by using Finite Element Analysis (FEA),which gave some suggestions for reference on how to determine the technological parameters for large-sized welding structures.

Abstract: Tubular evaporator is one of the key components of central air-conditioning. It is necessary to do aging treatment to relief residual stress and prevent leak phenomenon from structural deformation. Vibratory stress relief (VSR) can relieve residual stress in metal component. It has high efficiency with energy-saving, no exhausting and low cost. However vibration parameter impacts effect considerably. The author determines vibration parameter based on vibration mode and stress distribution. The relative parameters cover excitation frequency and point, support point etc. We measured residual stress both for after welding and VSR treatment lasting 30 minutes of the component. Result shows that residual stress is reduced by 61%. Residual stress between different points is decreased by 85.56% after VSR. Therefore, VSR should be carried out by vibration parameter based on vibration mode and stress distribution. At last we can say that our innovation is adapt to determine the VSR technical parameter for all metal components.

Abstract: In order to obtain the natural frequency, vibration mode and the curves of amplitude-frequency under two supporting ways, dynamic analysis was carried out on the large plane steel gate structures of a hydraulic projects. According to the Chinese machinery industry standard of vibration stress relief, technological parameters and effective range of vibratory stress relief were determined under two supporting ways. Some valuable references of determining technological parameters of vibratory stress relief for the plane steel gate structures and other momentous welding structures were provided through the research results and the conclusions.

Abstract: Cylindrical welded component is one of the typical components. It is necessary to do aging treatment for keeping stable dimension. Vibratory stress relief (VSR) is a new kind of technology which may eliminate the residual stress in metal component with high efficiency, energy-saving, environment protection and low cost compared with thermal stress relief (TSR). And the effect is greatly impacted by vibration parameter. Vibration modes are tested by modal analysis. Excitation frequency and point, support point and other parameter are determined by stress distribution and the fourth vibration mode of cylindrical welded component. Blind hole method is adopted to measure respectively component residual stress after welding and with 20 minutes of VSR treatment. Result shows that residual stress is reduced by 50% or so after VSR for cylindrical welded component. Therefore, vibratory parameters are determined by component residual stress distribution and its vibration mode. The best effect can be obtained for the technology of VSR.

Abstract: Considering that most of the research on vibratory stress relief (VSR) is excited by low-frequency vibration at present, high-frequency-exciting VSR on small Cr12MoV quenched specimens was studied. A high-frequency vibration table system was adopted as the exciter of the VSR. To increase the vibration level, a novel vibration level amplifying device was put forward. High-frequency VSR on the same group of small Cr12MoV quenched specimens was carried out under various vibration levels. The residual stress before and after vibration was comparatively analyzed. The results showed that the high-frequency vibration had the better effect on eliminating and homogenizing the residual stress and that increasing the vibration level of high-frequency-exciting could improve the effect of high-frequency VSR.

Abstract: The application of mechanical vibration has been known for many years, but some controversy still exists. According to some ideas the mechanical vibration reduces the technological stresses by summation of technological stress and stress from external loads (vibration). But on the other hand, the mechanical vibration causes more complicated phenomena (micro-relaxation) resulting in dimensional stability close to natural seasoning effects. In the present study authors present results of research into mechanical vibration from the experimental and practical point of view, proving that this process can be used to obtain dimensional stability. The results has also indicated that the reduction of the technological stresses is highly questionable.

Abstract: This paper proposes the method of multi-point VSR control system based on virtual instrument for the single-point aging cannot meet the problem of eliminating large and middle-sized the residual stress of workpieces. The system could achieve the setting of parameters on stress relief and the automatic controlling of the work process on PC by using LabVIEW as the development platform. By using data acquisition card USB-6229 BNC, it can realize the output voltage and the frequency pulse and the collection on the acceleration by the way of real-time and frequency variation sampling. At the same time, it has provided the theoretical basis for the effect of vibratory stress relief, and the system has realized the design and test in the laboratory, compared with the development method of single-point vibratory stress relief, this system has many advantages, such as the shorter aging cycle, the effect of eliminating residual stress and so on.