Academic literature on the topic 'Vibratory Stress Relief; Fatigue; Welding'
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Journal articles on the topic "Vibratory Stress Relief; Fatigue; Welding"
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Jurčius, Aurimas, Algirdas Vaclovas Valiulis, and Olegas Černašejus. "Effects of Vibration Energy Input on Stress Concentration in Weld and Heat-Affected Zone of S355J2 Steel." Solid State Phenomena 165 (June 2010): 73–78. http://dx.doi.org/10.4028/www.scientific.net/ssp.165.73.
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The existence of residual stresses induced by the welding process is an important reason of cracking and distortion in welded metal structures that may affect the fatigue life and dimensional stability significantly [1]. Heat treatment is one of the traditional methods to relieve the residual stresses. But it is often limited by the manufacturing condition and the size of the structures. In this paper a procedure called vibratory stress relief (VSR) is discussed. VSR is the process to reduce and re-distribute the internal residual stresses of welded structures by means of weldment mechanical vibration during welding. Parameters of VSR procedure are described in the paper. Residual stresses on weld bead are measured in three different specimens by X-ray diffraction method. Mechanical tests of welded specimens were also performed with purpose to evaluate VSR effect in weld metal and heat affected zone (HAZ).
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Rao, De Lin, Zheng Qiang Zhu, Li Gong Chen, and Chunzhen Ni. "Reduce the Residual Stress of Welded Structures by Post-Weld Vibration." Materials Science Forum 490-491 (July 2005): 102–6. http://dx.doi.org/10.4028/www.scientific.net/msf.490-491.102.
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The existence of residual stresses caused by the welding process is an important reason of cracking and distortion in welded metal structures that may affect the fatigue life and dimensional stability significantly. Heat treatment is one of the traditional methods to relieve the residual stresses. But it is often limited by the manufacturing condition and the size of the structures. In this paper a procedure called vibratory stress relief (VSR) is discussed. VSR is a process to reduce and re-distribute the internal residual stresses of welded structures by means of post-weld mechanical vibration. The effectiveness of VSR on the residual stresses of welded structures, including the drums of hoist machine and thick stainless steel plate are investigated. Parameters of VSR procedure are described in the paper. Residual stresses on weld bead are measured before and after VSR treatment by hole-drilling method and about 30%~50% reduction of residual stresses are observed. The results show that VSR process can reduce the residual stress both middle carbon steel (Q345) and stainless steel (304L) welded structures effectively.
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Almeida, Luiz Fernando Cursino Briet de, Julio Cesar Lourenco, Maria Ismenia Sodero Toledo Faria, Decio Lima Vieira, Alain Laurent Marie Robin, and Carlos Angelo Nunes. "Vibratory Stress Relief and Vibratory Weld Conditioning of Flux cored arc welded CA6NM steel." Journal of Materials Science Research 9, no. 1 (December 31, 2019): 32. http://dx.doi.org/10.5539/jmsr.v9n1p32.
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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.
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Duan, Neng Quan, Xiao Li, Wen Hua Du, and Xue Dou. "Simulation Research on Relieving Welding Residual Stress by Vibratory Stress Relief Technology." Advanced Materials Research 652-654 (January 2013): 2343–46. http://dx.doi.org/10.4028/www.scientific.net/amr.652-654.2343.
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Analysis of the causes of welding residual stress and the mechanism of VSR, also give the sufficient condition of the exciting force. Firstly, use the thermal - structural coupling and cell life and death of the welding process simulation, get the welding residual stress. Consistent with the theory. Secondly, build the VSR simulation process based on the use of the harmonic response analysis and welding simulation. select the appropriate VSR process parameters through the simulation results. Finally, VSR process simulation, analysis showed that the peak of residual stress after VSR treatment decreased by about 33%, and achieved good results. The numerical simulation analysis provides a strong basis for rational selection of the parameters of the VSR.
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Fu, Jian Ke, Xiao Hui Huang, and Liang Xu. "Numerical Simulation for Technological Parameters of Vibratory Stress Relief in Large Welding Structures." Applied Mechanics and Materials 217-219 (November 2012): 2046–50. http://dx.doi.org/10.4028/www.scientific.net/amm.217-219.2046.
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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.
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Dong, Xue Wu, Jian Hui Han, Dai Ren, Kai Mu, Dong Peng Liu, and Yao Li Du. "Vibratory Stress Relief of Central Air-Conditioning Evaporator." Applied Mechanics and Materials 397-400 (September 2013): 393–96. http://dx.doi.org/10.4028/www.scientific.net/amm.397-400.393.
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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.
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Kim, B. J., Y. R. Son, J. O. Yun, and Jeong Soo Lee. "Residual Stress Relief and Redistribution of Welded Metals by Vibratory Stress Relaxation." Materials Science Forum 580-582 (June 2008): 419–23. http://dx.doi.org/10.4028/www.scientific.net/msf.580-582.419.
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In this study, research work on the effects of vibrational energy on the microstructure of welds and Charpy toughness is performed. The results show that vibration during welding exhibits positive effects on the microstructure constituent formation by reducing the amount and thickness of grain boundary ferrite and suppressing the formation of the Widmanstatten structure. And also due to the finer microstructure developed by the vibration, toughness value of the weld metal increases.
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Rao,, Delin, Jingguo Ge, and, and Ligong Chen. "Vibratory Stress Relief in Manufacturing the Rails of a Maglev System." Journal of Manufacturing Science and Engineering 126, no. 2 (May 1, 2004): 388–91. http://dx.doi.org/10.1115/1.1644544.
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To reduce the welding induced residual stress in the rails of a magnetic levitation (maglev) transport system, the procedure of vibratory stress relief (VSR) is applied and discussed in this paper. Suitable welding sequence for the rails is introduced to keep the residual stress low. Qualitative analysis with scanning curve shows that the peak of acceleration becomes higher after the procedure of VSR and the resonant frequency becomes lower. It means that the procedure of VSR is effective according to the JB/T5926-91 standard. The residual stress in the rail was measured before VSR and after VSR, using hole-drilling method, and the result shows that the average principal stresses was reduced by about 30% after VSR.
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Chen, Shu-Guang, Yi-Du Zhang, Qiong Wu, Han-Jun Gao, and Dong-Yang Yan. "Residual Stress Relief for 2219 Aluminum Alloy Weldments: A Comparative Study on Three Stress Relief Methods." Metals 9, no. 4 (April 8, 2019): 419. http://dx.doi.org/10.3390/met9040419.
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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.
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Dong, Xue Wu, Yan Ting Wang, Jun Hong Cheng, Xi Zhang, Jian Hui Han, Yan Yan Yang, and Bing Li. "Study of the Vibratory Stress Relief for Large-Scale Parallel Welded Steel Truss." Applied Mechanics and Materials 740 (March 2015): 136–41. http://dx.doi.org/10.4028/www.scientific.net/amm.740.136.
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Parallel welded steel truss component is widely used in construction, tower, bridges, aerospace and other fields. And the welding residual stress is distributed complicatedly in many areas and directions, which will definitely deform the welded steel truss or even crack it. So, it is necessary to do aging treatment to avoid such thing happened, as well as improve the accuracy and reliability. 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). But its technical effects vary with the vibration parameters. To the parallel steel truss structures, the excitation parameter of VSR is determined by welding residual stress distribution and the natural mode of vibration. The residual stress concentration areas can get enough vibration, if the parallel steel truss component vibrates with different kinds of natural mode of vibration, which will obtain good effect of eliminating stress. Firstly, the inherent vibration mode of parallel welded steel truss component is measured by the modal analysis technology. Secondly, multiple intrinsic modes are chosen according to principle of making all the welding residual stress concentration regions and directions get enough vibration and then main technical parameters are determined such as excitation frequency, excitation point and support point. In this paper, two examples are given out: the specimen 1is treated with the transverse bending vibration mode and torsion vibration mode respectively according to the above method. As for specimen 2, it is treated with 3 exciting frequencies which are located automatically by the vibration aging machine. The residual stresses of the two specimens are measured before and after their vibrations with blind holes method. Results show that after vibration aging, the welding residual stress peak figure of the Specimen 1 is reduced by an average of 48.65% and the mean value of that dropped by an average of 32.50%. Correspondingly, the residual stress peak value of the Specimen 2 shows a decline of 3.38%, its average fell by an average of 2.55%.
Dissertations / Theses on the topic "Vibratory Stress Relief; Fatigue; Welding"
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Munsi, A. S. M. Younus. "Investigation and validation of vibratory methods for stress relieving and weld conditioning." Thesis, University of Strathclyde, 1999. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21439.
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Manufacturing processes inevitably induce a state of residual stress into materials and products. These residual stresses pose a large potential problem, in terms of dimensional stability and reduced fatigue life. Ideally, residual stresses should be reducible to low levels. There are three methods in general usage for the relaxation of these stresses, - Annealing, Shakedown and Vibratory Stress Relief (VSR). A previous study had suggested that vibration during and/or after welding may usefully modify residual stresses due to welding. This has been termed Vibratory Weld Conditioning (VWC). A comparative study of the methods is presented in section 1.4. The use of VSR, though widespread, has been adopted on a case-by-case basis, due to the lack of understanding of the processes at work. The purpose of this work was to investigate and validate the VSR/VWC method as a proposed alternative to the processes mentioned above. In order to do this a series of tests were devised in which the specimens were welded as a mechanism of stress induction. The residual stresses were measured before and after welding and vibration by means of a scanning X-ray diffractometer. In Chapter 1, the study of Residual Stress (source, formation etc), Welding Metallurgy and a comparison of VSR/VWC with other treatment methods are presented. In Chapter 2, a detailed review of literature is presented, where the accessible literature on VSR/VWC to date are included. In Chapter 3, the theoretical background of Modal Analysis, the Measurement of Dynamic Induced Stress and Measurement of Residual Stressesis discussed. In Chapter 4, the FE analysis of different structures is presented. In the FE analysis, different properties of the structures were determined using the FE model to aid the VSR/VWC study. The experimental investigations are presented in Chapter 5, which is divided into the following parts: Modal Analysis (experimental), Calibration of the X-ray measurements, VSR/VWC treatments, Cryogenic treatment, Fatigue Test and Metallurgical Investigation of VSR/VWC treated specimens. At the outset of the experimental work, the calibration of the X-ray diffractometer was carried out. After calibration of the X-ray and the X-ray Elastic Constant the error band of the diffractometer was significantly reduced. The practical modal analysis of the "8" frame was carried out to determine the modal characteristics of the frame to aid the VSR investigation of the frame. The VSR/VWC treatments are divided into "during welding" and "post weld" treatments and are presented in 10 different experiments. First, the "during welding" treatments were carried out. Investigation was started with application of tensile and compressive static stress to the specimens during welding and cooling. It was observed that the tensile induced stress decreased, and compressive induced stress increased the residual stresses. Rigid body motion (RBM) vibration showed no effect on the residual stresses. The cantilever beam test of the flexural vibration test showed some important characteristics, where the longitudinal residual stresses were found to decrease with application of small-induced stress. An increase in applied stress or time of vibration did not cause any more reduction. The transverse residual stresses increased with application of small-induced stresses. With increase in the applied stress the residual stresses decreased. High frequency vibration in both RBM and flexural vibration was found to be ineffective in reducing the residual stresses. The flexural vibration of the Four-Roller Supported beam showed a very confusing result, where no particular trend of the residual stresses was found. The combined mode of vibration (longitudinal and flexural) treatment showed no effect on residual stresses. The "post weld" treatment of the specimens showed a significant reduction in the residual stresses, where the reduction in the residual stresses were found to be a function of applied stress, while the vibration time effect was found to be negligible. A complex shape of reduction in the residual stresses were found along the width of the specimens, which made it impossible to develop any plastic flow model for the reduction in the residual stresses. Torsional test revealed a very important property of the residual stresses, where the residual stresses were found to decrease by a significant amount with application of very small induced stress. High induced stress only redistributed the residual stresses. Cryogenic treatment caused no reduction in the residual stresses. Contrarily the same specimen showed a significant reduction after VSR treatment. The fatigue test showed an increased fatigue life of the VSR treated specimens, while the thermally treated specimens showed a decreased fatigue life. The vibrated specimens showed highly oriented ferrite crystals in directions with Miller [111] to the stress axis. The hardness of the VSR treated specimens was found to increase significantly in comparison to the unvibrated specimens.
Book chapters on the topic "Vibratory Stress Relief; Fatigue; Welding"
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Jing, Song, Zhang Yidu, and Sun Ke. "The Numerical Simulation for Effect of Vibratory Stress Relief on Titanium Alloy Ti-6Al-4V Fatigue Life." In Theory, Methodology, Tools and Applications for Modeling and Simulation of Complex Systems, 530–39. Singapore: Springer Singapore, 2016. http://dx.doi.org/10.1007/978-981-10-2669-0_57.
Full textConference papers on the topic "Vibratory Stress Relief; Fatigue; Welding"
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MajidiRad, AmirHossein, and Yimesker Yihun. "Review of Welding Residual Stress Stiffening Effect on Vibrational Characteristics of Structures Using Damage Approach and Vibratory Stress Relief Implementation." In ASME 2017 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/detc2017-67993.
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There is a huge amount of research and study on the quality, parameter manipulation, material selection etc. of welding to develop optimized results for specific applications. To have a profound understanding of the process, and to investigate and verify various parameters which affect the quality of the welding process, experts use analytical, numerical and experimental methods. The major concern regarding the welding procedure is welding defect, which can affect the integrity of the welded structure. Various nondestructive structural health monitoring methods and modal analysis techniques have been employed to study and improve the strength and quality of the welded structure. Modal analysis is one of the most accurate and commercial techniques to track down the damage within the structures. It uses natural frequency, damping factors and modal shapes to observe the structural and material defects in details. There have been noticeable developments in this area and lots of studies have been conducted applying this technique to put welding procedure under rigorous scrutiny to improve its efficiency. While modal analysis is a tool to identify structural integrity of the components, vibration can affect the nature of the metal and change the mechanical properties in some cases. Mechanical vibration and Ultrasonic as low and high frequency oscillations respectively, are able to change the microstructure of the structures so that dislocations move, hence the stress trapped within will redistribute. This redistribution can lead to residual stress reduction up to a level. In this review paper, all remarks above are considered, defined and accurately studied through various cases in order to address different application of vibratory stress relief and recent achievement in this field.
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Song, Jing, Yidu Zhang, and Ke Sun. "The numerical simulation of the influence of orientational vibratory stress relief to aluminium alloy 7075-T651 fatigue life." In 2015 2nd International Conference on Machinery, Materials Engineering, Chemical Engineering and Biotechnology. Paris, France: Atlantis Press, 2016. http://dx.doi.org/10.2991/mmeceb-15.2016.148.
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Manteghi, Siak, Dave Gibson, and Carol Johnston. "Fatigue Performance of Friction Welds Manufactured Both in Air and Underwater." In ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/omae2017-62495.
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Friction welding is being performed offshore in environments where arc welding may be difficult and where fatigue performance is critical. Friction welding underwater with Remotely Operated Vehicles (ROVs) can greatly reduce the cost of a project compared with using divers and arc welding because the support vessel, which is the major cost component in such an operation, is smaller. This paper describes two different programs of experimental work in which the fatigue endurance of friction welds were found to be better than that which could be expected from arc welded joints of similar geometry. The first program involved experimental work done with 25mm diameter steel bars. It found that, in the as-welded condition, friction welds have high fatigue strength. Residual stress measurements showed that this was due to a beneficial residual stress distribution in which compressive stresses are present at the surface adjacent to the failure site. Further evidence of this was obtained by subjecting some specimens to thermal stress relief. The fatigue strength of the stress relieved specimens was reduced compared with the as-welded joints but nevertheless the fatigue strength of these specimens was still high. The second program involved fatigue tests on friction stud welds in which the friction welding equipment was deployed offshore by divers or ROVs. The test specimens were made up of 19mm diameter studs friction welded onto structural steel plate. As with the first program, the specimens showed high fatigue endurance with results approximating to a DNV Class C1 curve. In some of the tests, the studs were preloaded in tension and results from specimens that were preloaded to the correct value specified for the joint were all stopped as run-outs, with specimens remaining unbroken.
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Gilles, Ph, S. Courtin, R. Vincent, M. Yescas, and F. Gommez. "Methodology for Numerical Welding Simulation Validation: The Dissimilar Metal Weld Case." In ASME 2013 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/pvp2013-97475.
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Welding processes induce residual stresses and distortion in the welded joint and the connected components. For manufacturing purpose distortion is the main issue and up to now the problem is handled by post weld corrective actions. Welding residual stress fields are not considered at the design stage in French codes and standards. However, it is well known that residual stresses are likely to increase the risks of fatigue or corrosion and may cause failure in brittle materials. Ferritic parts of large components are post-weld heat treated; allowing disregarding the influence of residuals stresses thanks to their relief. Preventive measures, including mitigation by fine polishing are undertaken in corrosion sensitive zones. The influence of residual stresses on fatigue is more complex to analyze: in low cycle fatigue, residual stresses should be relieved or redistributed after few cycles with plastic straining, and for high cycle fatigue, residual stress effects are accounted for through a mean stress offsett. When considered, residual stress fields are often represented in a very crude manner by a membrane distribution of the most influent stress component through the thickness of the structure. In a less rough way, several codes or fitness-for-purpose guidelines (API [1], British standards [2]) propose residual stress profiles relative to several weld configurations. Nevertheless for a given case, the given profiles may differ significantly for several reasons: the degree of conservatism, the number of covered cases, the embedded margins accounting for uncertainties. Some ill-posed benchmark problems have shown that numerical simulation of residual stresses may deliver very scattered results. AREVA has therefore developed a methodology to validate welding simulations. The scope is limited to fusion welding. The simulations are based on a Thermo-Metallurgical Mechanical model in which the welding energy is represented by an equivalent heat source. This paper presents the actual state of development of this methodology which will be illustrated through 4 examples of residual fields in Dissimilar Metal Welds. Residual stress measurements have been performed for each of the four mock-ups by different techniques. Based on this important experimental and numerical campaign some actions of improvement of the validation methodology are finally listed.
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Satyambabu, K., and N. Ramachandran. "Feasibility Studies on the Modeling and Evaluation of Residual Stresses in Arc Welded Butt Joints." In ASME 8th Biennial Conference on Engineering Systems Design and Analysis. ASMEDC, 2006. http://dx.doi.org/10.1115/esda2006-95176.
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Many important engineering applications such as nuclear reactors, ships, pipes and pressure vessels are shell-like structures made with weldments. For such a structure, a major problem is the development of residual stress and distortion due to welding. Residual stresses in weldments significantly affect stress corrosion cracking, hydrogen-induced cracking and fatigue strength in welded structures. As-welded components generally have certain amount of residual stresses caused by the application of intense heat or thermal loading at the weld joint, formed due to non-uniform cooling rates at different points in the weld metal and heat affected zones. Presence of residual stresses in a component is detrimental as they may lead to failure below the design stress value and also affect many important properties including the life of a welded component. Welding induced residual stresses can significantly increase the fracture driving force in a weldment and also contribute to brittle fracture. The thermal cycle imposed on any welded object causes thermal expansions and contractions which are not uniform. Quantitative measurement of residual stresses is essential to take remedial measures such as change in the welding technique, optimizing welding parameters (heat input, electrode diameter etc,), change in the weld groove design and post-weld heat treatment for minimizing the residual stresses. Residual stress measurements after post-weld treatment would also ensure the adequacy of stress relief treatment. To have an investigation into these aspects, residual stresses due to Manual Metal Arc Welding and Submerged Arc Welding were measured nondestructively with Ultrasonic technique. Residual stress distribution for Shielded Metal Arc Welding and Submerged Arc Welding were compared and the present studies emphasized, that Shielded Metal Arc Welding gave higher compressive stresses than Submerged Arc Welding. Further, to substantiate the studies, commercial finite element analysis software ANSYS 5.6 was used for modeling of manual metal arc welded joint. The results obtained by ANSYS were compared with those by Ultrasonic method.
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Mazur, Zdzislaw, and Alejandro Herna´ndez-Rossette. "Failure Evaluation of the Compressor Vanes of Combined Cycle Unit." In ASME 2010 Power Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/power2010-27071.
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A compressor blade failure was experienced on a 69 MW gas turbine of a combined cycle (C.C.) unit after four years operation since its last overhaul (January 2005). The unit accumulated 27,000 service hours and 97 start-ups since the last overhaul. This unit consists of four gas turbine stages and 19 compressor stages and operates at 3600 rpm. In 2006, the unit was equipped with a fogging system at the compressor air inlet duct to increase unit power output during high ambient temperature days (hot days). These fog water nozzles were installed upstream of the compressor inlet air filter without any water filter/catcher before the water spray nozzles. Three unit failure events occurred within a small time period, which caused a forced outage. The first failure occurred in December 2008, a second event in March 2009 and the third event in May 2009. Visual examination carried out after the first failure indicated that the compressor vanes (diaphragms) had cracks in their airfoil initiating at the blade tenons welded to the diaphragm outer shroud at stages 3, 8, 9, 10 and 11. Also, a number of stationary vanes and blades at each stage of the compressor showed foreign object damage (FOD) and fractures at the airfoil. Visual examination performed for the second failure event after 60 unit operating hours indicated that many compressor vanes (diaphragms) and blades had FOD at the airfoil. This was attributed to fractures caused by the fogging system. The water spray carried over in the compressor flow path at high velocity causing the FOD damage. Visual examination completed upon the third failure event after two unit startup attempts indicated damage of compressor stationary vanes and blades, principally at stages 12 to 16, and also stages 17 to 19. The damage consisted of airfoil fracture in the stationary vanes and blades, FOD, blade tip rubbing, and bending of the stationary vanes, blades and diaphragm shrouds. A laboratory evaluation of stationary vane tenon fracture indicated a high cycle fatigue (HCF) failure mechanism, and crack initiation was accelerated by corrosion pitting on blade surfaces due to high humidity air generated by the fogging system. Stationary vane damage was caused by a rotating stall phenomenon, which generates vibratory stress in stationary vanes and blades during unit start-ups. During the third failure event, the stationary vane HCF damage was highly accelerated due to pre-existing partial fractures in the tenons generated during previous failure events which had not been detected by non-destructive tests. Stationary vane and moving blade failure was also influenced by high tenon brittleness in stationary vanes and blades generated during manufacture by welding the diaphragms, and repair welding the blades without adequate post-weld heat treatment (stress relieving). A compressor stationary vane and blade failure evaluation was completed. This investigation included cracked blade metallographic analysis, unit operation parameter analysis, history-of-events analysis, and crack initiation and propagation analysis. This paper provides an overview of the compressor failure investigation, which led to the identification of the HCF failure mechanism generated by rotating stall during unit start-ups, highly accelerated corrosion generated by the fogging system, and high brittleness in the stationary vanes and blades as the primary contribution to the observed failure.
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Mazur, Zdzislaw, Alejandro Herna´ndez-Rossette, and Jesu´s Porcayo-Caldero´n. "Failure Investigation of the 69 MW Gas Turbine of Combined Cycle Unit." In ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-22262.
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A compressor blade failure was experienced at the 69 MW gas turbine of a combined cycle (C.C.) unit after four years operation since the last overhaul (January 2005). The unit accumulated 27,000 service hours and 97 start-ups since the last overhaul. This unit consists of four gas turbine stages and 19 compressor stages and operates at 3600 rpm. In 2006, the unit was equipped with a fogging system at the compressor air inlet duct to increment unit power output during high ambient temperature days (hot days). These fog water nozzles were installed upstream of the compressor inlet air filter without any water filter/catcher before the water spray nozzles. Three unit failure events occurred at small periods, which caused forced outage. The first failure occurred in December 2008, a second event in March 2009 and the third event in May 2009. Visual examination carried out after the first failure event indicated that the compressor vanes (diaphragms) had cracks in their airfoils initiating at blade tenons welded to the diaphragm outer shroud at stages 3, 8, 9, 10 and 11. Also, many stationary vanes and moving blades at each stage of the compressor showed foreign object damage (FOD) and fractures at the airfoil. Visual examination performed for the second failure event after 60 unit operation hours indicated that many compressor vanes (diaphragms) and moving blades had FOD at the airfoil. This was attributed to fractures of the fogging system water spray nozzle, which were then induced to the compressor flow path channel at high velocity causing the above-mentioned damage. Visual examination completed upon the third failure event after two unit startup attempts indicated damage of compressor stationary vanes and moving blades principally at stages 12 to 16, and also stages 17 to 19. The damage consisted of airfoil fracture in stationary vanes and moving blades, FOD, moving blade tip rubbing, and bending of stationary vanes, moving blades and diaphragm shrouds. A laboratory evaluation of stationary vane tenon fracture indicated a high cycle fatigue (HCF) failure mechanism, and crack initiation was accelerated by corrosion picks on blade surfaces due to high humidity air generated by the fogging system. Stationary vane damage was caused by a rotating stall phenomenon, which generates vibratory stresses in stationary vanes and moving blades during unit start-ups. During the third failure event, stationary vane HCF damage was highly accelerated due to pre-existent partial fractures in tenons generated during previous failure events, which had not been detected by non-destructive tests. Stationary vane and moving blade failure was also influenced by high tenon brittleness in stationary vanes and moving blades generated during manufacture by welding (diaphragms) and repair welding (moving blades) without adequate post-weld heat treatment (stress relieving). A compressor stationary vane and moving blade failure evaluation was completed. This investigation included cracked blade metallographic analysis, unit operation parameter analysis, history-of-events analysis, and crack initiation and propagation analysis. This paper provides an overview of the compressor failure investigation, which led to identification of the HCF failure mechanism generated by rotating stall during unit start-ups, highly accelerated by corrosion generated by the fogging system and influenced by high stationary vane and moving blade brittleness as the primary contribution to the observed failure.