Prediction of Residual Stress Improvement by Water Jet Peening Using Cavitating Jet Simulation With Bubble Flow Model

2010 ◽  
Author(s):  
Masashi Fukaya ◽  
Ren Morinaka ◽  
Noboru Saitou ◽  
Hisamitsu Hatou ◽  
Yoshiaki Tamura ◽  
...  
Keyword(s):  
Residual Stress ◽  
Flat Plate ◽  
Power Plants ◽  
Compressive Residual Stress ◽  
Flow Model ◽  
Water Jet ◽  
Bubble Collapse ◽  
Bubble Flow ◽  
Bubble Pressure ◽  
Cavitating Jet

We developed the new method for predicting a region of compressive residual stress on the weld surface after water jet peeing (WJP), which is a preventive maintenance technology for nuclear power plants. A cavitating jet is impinged on the weld surfaces of structures in a nuclear reactor. Bubble collapse impact causes plastic deformation of the weld surface, and changes the residual stress from tensile to compressive. Compressive residual stress prevents the occurrence of stress corrosion cracking (SCC) on the weld surface. A cavitating jet vertically injected into a submerged flat plate was investigated. Tensile stress was introduced onto the surface of the stainless steel plate by grinding before WJP in the experiment. We numerically simulated impulsive bubble pressure that varied by microseconds in the cavitating jet with the “bubble flow model”. The bubble flow model simulates the abrupt time-variations in the radius and inner pressure of bubbles based on the Rayleigh-Plesset equation in a cavitating flow. The cavitation collapse energy was estimated based on the bubble pressure. The cavitation collapse energy was compared with the measured compressive residual stress on the flat plate after WJP. The radial range of the compressive residual stress from the jet center axis is one of the most important measures of performance of WJP. The radial range of the cavitation collapse energy corresponded to that of compressive residual stress with a prediction error of +/− 20% under different conditions of jet velocity and the distance between the jet nozzle and plate surface. The results confirmed that the method we developed for predicting the region of compressive residual stress after WJP was valid.

Mitigation of Stress Corrosion Cracking Based on Residual Stress Improvement by Water Jet Peening (WJP)

2011 ◽  
Author(s):  
Masashi Fukaya ◽  
Fujio Yoshikubo ◽  
Hisamitsu Hatoh ◽  
Yuji Matsui ◽  
Yoshiaki Tamura ◽  
...  
Keyword(s):  
Residual Stress ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Nuclear Power ◽  
Water Jet ◽  
Corrosion Cracking ◽  
Bubble Collapse ◽  
Bubble Pressure ◽  
Stress Simulation ◽  
Cavitating Jet

We have developed a practical peening technology using cavitating water jet. Water jet peening (WJP) is a preventive maintenance technology for nuclear power plants. WJP changes the residual stress on weld surfaces of reactor internals from tensile to compressive to mitigate the stress corrosion cracking (SCC). The operating conditions of WJP are controlled on the basis of ‘JSME Codes for Nuclear Power Generation Facilities.’ WJP has several advantages of operation, especially no foreign material is left in the reactor vessel since only water is injected, and wide range of the residual stress improvement is obtained since the cavitating flow spreads along the weld surface. We have also developed a prediction method of the residual stress improvement by WJP using a combination of a cavitating jet simulation and a residual stress simulation. We numerically simulated impulsive bubble pressure that varied in microseconds in the cavitating jet with ‘bubble flow model’. The bubble collapse energy was estimated by the bubble pressure. The residual stress simulation was conducted under the input conditions obtained from the bubble collapse energy. The residual stress distributions on and under the weld surface were predicted. The distributions were compared with measured data, and the result confirmed that the developed method for predicting the compressive residual stress after WJP was valid.

Use of Cavitating Jet for Introducing Compressive Residual Stress

1999 ◽  
Vol 122 (1) ◽  
pp. 83-89 ◽  
Author(s):  
H. Soyama ◽  
J. D. Park ◽  
M. Saka
Keyword(s):  
Residual Stress ◽  
Exposure Time ◽  
High Speed ◽  
Compressive Residual Stress ◽  
Diffraction Method ◽  
Water Jet ◽  
Material Surface ◽  
Principal Stresses ◽  
Plane Normal ◽  
Cavitating Jet

In an attempt to strengthen the surface of materials, the potential of using a cavitating jet to form compressive residual stress has been investigated. Introducing compressive residual stress to a material surface provides improvement of the fatigue strength and resistance to stress corrosion cracking. In general, cavitation causes damage to hydraulic machinery. However, cavitation impact can be used to form compressive residual stress in the same way as shot peening. In the initial stage, when cavitation erosion progresses, only plastic deformation, without mass loss, takes place on the material surface. Thus, it is possible to form compressive residual stress without any damage by considering the intensity and exposure time of the cavitation attack. Cavitation is also induced by ultrasonic, high-speed water tunnel and high-speed submerged water jet, i.e., a cavitating jet. The great advantage of a cavitating jet is that the jet causes the cavitation wherever the cavitation impact is required. To obtain the optimum condition for the formation of compressive residual stress by using a cavitating jet, the residual stresses on stainless steel (JIS SUS304 and SUS316) and also copper (JIS C1100) have been examined by changing the exposure time of the cavitating jet. The in-plane normal stresses were measured in three different directions on the surface plane using the X-ray diffraction method, allowing for the principal stresses to be calculated. Both of the principal stresses are found changing from tension to compression within a 10 s exposure to the cavitating jet. The compressive residual stress as a result of the cavitating jet was found to be saturated after a certain time, but it starts decreasing, and finally, it approaches zero asymptotically. It could be verified in the present study that it was possible to form compressive residual stress by using a cavitating jet, and the optimum processing time could also be realized. The great difference between the water jet in water and air has also been shown in this regard. [S1087-1357(00)00501-3]

Improvement of Fatigue Strength by Using Cavitating Jet in Air

2004 ◽  
Author(s):  
Hitoshi Soyama ◽  
Dan Macodiyo
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
High Speed ◽  
Diffraction Method ◽  
Water Jet ◽  
Bubble Collapse ◽  
Surface Residual Stress ◽  
Hydraulic Machinery ◽  
Rotating Bending Fatigue ◽  
Cavitating Jet

Cavitation normally causes severe damage in hydraulic machinery such as pumps and valves. However, the cavitation impacts at the bubble collapse can be used to enhance the surface of metallic materials just as the same way as shot peening. In case of peening using cavitation impact, the cavitation is produced by injecting a high-speed water jet in a water-filled chamber. The authors have already demonstrated the fatigue strength improvement of materials using a high-speed water jet in water. Recently the authors succeeded in producing a cavitating jet in air by injecting a high-speed water jet into a low-speed water jet using a concentric nozzle. Cavitating jet in air can be used to peen parts of plant which cannot peened by the water-filled chamber, thereby impeding the initiation and/or the development of cracks. In this study, in order to demonstrate the improvement of fatigue strength of materials using cavitating jet in air, stainless steel (JIS SUS316L) was peened and the residual stress measured using the X-ray diffraction method. The surface residual stress of non-peened and peened specimen was −68 MPa and −350 MPa, respectively. The fatigue strength of the specimen were then investigated using the rotating bending fatigue test, with a stress ratio of R = −1. The fatigue strength of peened specimen by cavitating jet in air improved by 20% compared with nonpeened specimen.

Introduction of Compressive Residual Stress Using a Cavitating Jet in Air

2004 ◽  
Vol 126 (1) ◽  
pp. 123-128 ◽  
Author(s):  
Hitoshi Soyama
Keyword(s):  
Residual Stress ◽  
Mass Loss ◽  
Shot Peening ◽  
High Speed ◽  
Compressive Residual Stress ◽  
Injection Pressure ◽  
Water Jet ◽  
Low Speed ◽  
Aluminum Specimen ◽  
Cavitating Jet

Cavitation impact from a cavitation jet, which is formed from bubbles induced by a high-speed water jet in water, can be used for surface modification in a similar manner to shot peening. A cavitating jet is normally produced by injecting a high-speed water jet into a water-filled chamber. It is possible to make a cavitating jet in air by injecting a high-speed water jet into a concentric low-speed water jet that surrounds the high-speed jet. In order to demonstrate this, a high-speed water jet with a concentric low-speed water jet was impacted onto an aluminum specimen to observe the pattern of erosion. The mass loss of the specimen was weighed to measure the capability of the jet, since a more powerful jet produces a larger mass loss. It was shown that the combination of high- and concentric low-speed water jets produced a typical erosion pattern such as that obtained using a cavitating jet in a water-filled chamber. When the injection pressure of the concentric low-speed water jet was optimized, the capability of the cavitating jet in air was much greater than that of a cavitating jet in a water-filled chamber. It was demonstrated that an optimized cavitating jet in air introduced more compressive residual stress in the surface of tool steel alloy than that from a cavitating jet in a water-filled chamber. In addition, this stress was larger than that induced by shot peening. The peened surface was also less rough compared with shot peening.

Mechanism of Compressive Residual Stress Introduction on Surfaces of Metal Materials by Water-Jet Peening

2010 ◽  
Author(s):  
Ryo Ishibashi ◽  
Hisamitsu Hato ◽  
Fujio Yoshikubo
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Shock Waves ◽  
Power Plants ◽  
Compressive Residual Stress ◽  
Water Jet ◽  
Pulse Load ◽  
Depth Profiles ◽  
Impact Processes ◽  
The Impact

Water-jet peening (WJP) has been applied to several Japanese nuclear power plants as a method of preventive maintenance against stress corrosion cracking. WJP introduces compressive residual stress reaching hundreds of micrometers in depth, comparable with shot peening (SP), and much smaller plastic deformation at the processed surfaces than SP does. The causes of these features are investigated from the perspective of the impact processes on the surfaces. Pulse-load propagation simulation through elasto-plastic calculations using a finite-element method program was applied to analyze the effects of various parameters of the impact processes on the depth profiles of the residual stress and the amount of plastic deformation on the surface of austenitic stainless steels processed with either WJP or the SP. The calculated depth profiles of residual stress and plastic deformation were similar in some degree to the experimental results of an XRD residual-stress analysis and a plastic-strain analysis using both cross-sectional hardness measurements and EBSD analysis. The analysis reveals that the depth of the compressive residual stress tends to increase as the size of the loaded spot during impact increases. The average and maximum observed load spots using WJP were 0.25 and 0.95 mm in diameter, respectively. These diameters were respectively 1.3 and 4.8 times as large as the calculated diameter of a load spot using SP. The reason that the depth of the compressive residual stress using WJP is comparable with that using SP is considered to be the fact that the sizes of the load spots during the impact with WJP are in the same range as those with SP. Shots impact the surface during the SP process, while shock waves generated by the extinction of cavitations impact the surface during the WJP process. The analysis reveals that the shots deform the surface locally with much higher surface pressure in the early stages of the impact, while shock waves deform the surface evenly throughout the wave passage across the surface. It is inferred from these analyzed results that the media impacting the surface make a difference in the hardness and microstructure of the processed surface.

Modification of Microstrucure and Residual Stress on Friction Welding Surface of Titanium Alloy by Water-Jet Cavitation Peening

2011 ◽  
Vol 317-319 ◽  
pp. 429-435 ◽  
Author(s):  
Dong Ying Ju ◽  
Xin Mao Fu ◽  
Shun Na ◽  
Bing Han ◽  
Xiao Hu Deng
Keyword(s):  
Electron Microscopy ◽  
Residual Stress ◽  
Welded Joints ◽  
Compressive Residual Stress ◽  
Welded Joint ◽  
Water Jet ◽  
X Ray Diffraction ◽  
X Ray ◽  
Welding Surface ◽  
Scanning Electron

Water jet cavitation peening is applied to improve the strength and mechanical properties of the friction-welded joints of titanium alloys. Scanning electron microscopy observations of the microstructure of the welded joints and welded area before/after water jet cavitation peening confirm slip dislocation at the microstructure near the surface of the specimens. The residual stress on the surface of the welded joint is measured by X-ray diffraction. The results indicate the effect of peening time on the strength of compressive residual stress.

Long Term Stability of Compressive Residual Stress Introduced in Alloy 600 by Water Jet Peening Under Elevated Temperature Environment

2011 ◽  
Author(s):  
Tadafumi Hashimoto ◽  
Yusuke Osawa ◽  
Masashi Kameyama ◽  
Shinro Hirano ◽  
Naoki Chigusa ◽  
...  
Keyword(s):  
Residual Stress ◽  
Elevated Temperature ◽  
Stress Relaxation ◽  
Compressive Residual Stress ◽  
Water Jet ◽  
Target Area ◽  
Pressurized Water ◽  
Plastic Deformations ◽  
Term Operation

Primary water stress corrosion cracking (PWSCC) in the weld metal of alloy600 is an issue of concern in a pressurized water reactor (PWR). As a countermeasure against PWSCC, water jet peening (WJP), which can change tensile residual stress into compressive residual stress, has been applied to welded joints. Microstructure in the target area of WJP has an influence of not only WJP but welding and machining. Especially machining introduces severe plastic deformations to the materials. So microstructure in the target area might lack thermal stability due to severe plastic deformation. Additionally the region that compressive residual stress by WJP is nearly up to 1mm from the surface of the target material. As PWRs are operated at about 596K for long term, the compressive residual stress by WJP may be relieved due to creep. In order to keep operating PWRs safety, the stability of the compressive residual stress by WJP at elevated temperature has been clarified. In this work, the results were obtained written below. As a result of thermal aging test, a relaxation of compressive residual stress at specimen surface layer occurred due to recovery of the plastic deformations by machining. This stress relaxation behavior followed Johnson-Mehl equation. However residual stress relaxation due to creep was very few. Therefore it has suggested that the compressive residual stress introduced in Alloy600 by WJP is confirmed to remain stable during long term operation under elevated temperature.

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