To improve the rock breaking ability, cavitating waterjet and abrasive waterjet are combined by using a coaxial low-speed waterjet generated around the periphery of a high-speed abrasive waterjet, and a new type of wa...To improve the rock breaking ability, cavitating waterjet and abrasive waterjet are combined by using a coaxial low-speed waterjet generated around the periphery of a high-speed abrasive waterjet, and a new type of waterjet called unsubmerged cavitating abrasive waterjet(UCAWJ) is thus produced. The rock breaking performance of UCAWJ was compared with submerged cavitating abrasive waterjet(SCAWJ)and unsubmerged abrasive waterjet(UAWJ) by impinging sandstone specimens. Moreover, the effects of jet pressure, standoff distance, abrasive flow rate and concentration were studied by evaluating the specific energy consumption, and the area, depth, and mass loss of the eroded specimen. The results show that the artificially generated submerged environment in UCAWJ is able to enhance the rock breaking performance under the same operating parameters. Furthermore, the rock breaking performance of UCAWJ is much better at higher jet pressures and smaller standoff distances when compared with UAWJ. The greatest rock breaking ability of UCAWJ appears at jet pressure of 50 MPa and standoff distance of 32 mm, with the mass loss of sandstone increased by 370.6% and the energy dissipation decreased by 75.8%. In addition, under the experimental conditions the optimal abrasive flow rate and concentration are 76.5 m L/min and 3%, respectively.展开更多
This paper deals with an assessment of the machined surface created by abrasive waterjet technology regarding its cutting performance versus profile, lagging and waterjet angle assessments. The results of the experime...This paper deals with an assessment of the machined surface created by abrasive waterjet technology regarding its cutting performance versus profile, lagging and waterjet angle assessments. The results of the experiments presented in this study are with regard to Carrara marble. The machined surfaces were measured in seven different locations across a 40 mm depth of cut by a high precision contact-type profilometer and thus assessed using the standardized amplitude parameters of the profile distribution. The lagging and waterjet angle were also evaluated by creating a digital photo of the machined surface together with a reference gauge. The existence of machining marks on the machined surface has been mostly noticeable in the bottom zone around ~20 mm depth of cut down to jet exit. This investigation leads to a conclusion that, stand-off distance and traverse rate play the roles of the utmost importance in considerations of the machined surface quality in contrast to abrasive mass flow rate. In addition, while the striation zone (rough surface) cannot be eliminated entirely, by selecting proper process parameters, a smooth cutting machined surface can be accomplished.展开更多
In dealing with abrasive waterjet machining(AWJM) simulation,most literatures apply finite element method(FEM) to build pure waterjet models or single abrasive particle erosion models.To overcome the mesh distorti...In dealing with abrasive waterjet machining(AWJM) simulation,most literatures apply finite element method(FEM) to build pure waterjet models or single abrasive particle erosion models.To overcome the mesh distortion caused by large deformation using FEM and to consider the effects of both water and abrasive,the smoothed particle hydrodynamics(SPH) coupled FEM modeling for AWJM simulation is presented,in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FEM.The two parts interact through contact algorithm.Utilizing this model,abrasive waterjet with high velocity penetrating the target materials is simulated and the mechanism of erosion is depicted.The relationships between the depth of penetration and jet parameters,including water pressure and traverse speed,etc,are analyzed based on the simulation.The simulation results agree well with the existed experimental data.The mixing multi-materials SPH particles,which contain abrasive and water,are adopted by means of the randomized algorithm and material model for the abrasive is presented.The study will not only provide a new powerful tool for the simulation of abrasive waterjet machining,but also be beneficial to understand its cutting mechanism and optimize the operating parameters.展开更多
A study is carried out which analyzes the machinability of polymer matrix composites under an abrasive waterjet (AWJ) and the associated erosive process or mechanism. It shows that AWJ cutting can produce good quality...A study is carried out which analyzes the machinability of polymer matrix composites under an abrasive waterjet (AWJ) and the associated erosive process or mechanism. It shows that AWJ cutting can produce good quality kerf at high production rate if the cutting parameters are properly selected. A scanning electron microscopy (SEM) analysis of the cut surfaces reveals that the erosive process for the matrix material (resin) involves shearing and ploughing as well as intergranular cracking, while shearing is a dominant process for cutting the fibres in the upper cutting region but the fibers are mostly pulled out in the lower region.展开更多
The current research on self-resonating cavitating waterjet(SRCW) mainly focuses on the generation mechanism and structure optimization.Researches relating to the influences of disturbances at nozzle inlet on the ch...The current research on self-resonating cavitating waterjet(SRCW) mainly focuses on the generation mechanism and structure optimization.Researches relating to the influences of disturbances at nozzle inlet on the characteristics of the jet are rarely available.In order to further improve the performance of SRCW,effects of area discontinuity(enlargement and contraction) are experimentally investigated using three organ-pipe nozzles.Axial pressure oscillation peak and amplitude as well as aggressive erosion intensity of the jet are used to evaluate the effects.The results reveal that area enlargement and contraction affect the peak differently,depending on the inlet pressure,nozzle geometry,and standoff distance;while area contraction always improves the amplitude regardless of these factors.At inlet pressures of 10 MPa and 20 MPa,area discontinuity improves the peak at almost all the testing standoff distances,while this only happens at smaller standoff distances with the inlet pressure increased to 30 MPa.The capability of area discontinuity for improving the amplitude is enhancing with increasing inlet pressure.Moreover,the cavitation erosion ability of the jet can be largely enhanced around the optimum standoff distance,depending on the type of area discontinuity and nozzle geometry.A preliminary analysis of the influence of area discontinuity on the disturbance waves in the flow is also performed.The proposed research provides a new method for effectively enhancing the performance of SRCW.展开更多
Abrasive waterjet(AWJ)fracturing has become an accepted horizontal multistage stimulation technique due to its flexibility and high efficiency of extensive fracture placement.The downhole tool failure of AWJ fracturin...Abrasive waterjet(AWJ)fracturing has become an accepted horizontal multistage stimulation technique due to its flexibility and high efficiency of extensive fracture placement.The downhole tool failure of AWJ fracturing becomes an issue in the massive hydraulic fracturing because of high velocity and proppant erosion.This paper proposed a 3D computational fluid dynamics(CFD)-based erosion model by considering high-velocity waterjet impact,proppant shear erosion,and specific inner structure of hydra-jet tool body.The discrete phase approach was used to track the proppant transport and its concentration distribution.Field observation provides strong evidence of erosion patterns and mechanisms obtained from CFD simulation.The results show that the erosion rate has a space dependence in the inner wall of the tool body.The severe erosion areas are primarily located at the entries of the nozzle.Evident erosion patterns are found including a‘Rabbit’s ear’erosion at the upper-layer nozzles and a half bottom loop erosion at the lower-layer nozzles.Erosion mechanisms attribute to high flow velocity at the entry of nozzles and the inertia force of proppant.Sensitivity analysis demonstrates that the pumping rate is a primary factor contributing to erosion intensity.展开更多
Comminution of coal to ultrafine sizes by high-pressure waterjet provides a novel method for preparation of coal-water fuels for next generation,near-zero emission electric power generation.The particle size distribut...Comminution of coal to ultrafine sizes by high-pressure waterjet provides a novel method for preparation of coal-water fuels for next generation,near-zero emission electric power generation.The particle size distribution(PSD)of ground coal is a key parameter in the preparation of slurries as it determines the settling behavior of the particles and viscosity of the coal-water mixture.There are several methods available for representation and evaluation of particle size analysis data.However,fractal theory provides a means by which the entire PSD of comminuted materials can be quantified by using of a specific and exact value.In this paper,a volume-based fractal model was deduced to characterize the PSD of the coal which is ground in a specially designed comminution cell.During the size reduction process,the inlet pressures up to 276 MPa were used.展开更多
The fabrication of miniature structures on components with high-integrity surface quality represents one of the cutting edge technologies in the 21st century.The materials used to construct such small structures are o...The fabrication of miniature structures on components with high-integrity surface quality represents one of the cutting edge technologies in the 21st century.The materials used to construct such small structures are often difficult-to-machine.Many other readily available technologies either cannot realise necessary precision or are costly.Abrasive waterjet(AWJ)is a favourable technology for the machining of difficult-to-machine materials.However,this technology is generally aimed at large stock removal.A reduction in the scale of this technology is an attractive avenue for meeting the pressing need of industry in the production of damage-free micro features.This paper reviews some of the work that has been undertaken at UNSW Sydney about the development of such an AWJ technology,focusing on the system design currently employed to generate a micro abrasive jet,the erosion mechanisms associated with processing some typical brittle materials of both single-and two-phased.Processing models based on the findings are also presented.The review concludes on the viability of the technology and the prevailing trend in its development.展开更多
A computational fluid dynamics(CFD)study of the impact characteristics and stagnation formation on a solid target surface by an abrasive waterjet at supersonic velocities is presented to understand the impact process....A computational fluid dynamics(CFD)study of the impact characteristics and stagnation formation on a solid target surface by an abrasive waterjet at supersonic velocities is presented to understand the impact process.A CFD model is developed and verified by experimental water and particle velocities and then used to simulate the jet impact process.The trends of the stagnation formation and its effect on the jet flow with respect to the jetting and impacting parameters are amply discussed.It is found that stagnation formation at the impact site increases with an increase in the impact time,nozzle standoff distance and nozzle diameter,while the initial peak velocity at the nozzle exit has little effect on the size of the stagnation zone.It is shown that stagnation markedly changes the water and particle flow direction,so that the particle impact angle is varied and the jet impact area is enlarged.The jet structure may be classified to have a free jet flow region,a jet deflection region with a stagnation zone and a wall jet region.Furthermore,the stagnation affects significantly the waterjet and particle energy transferred to the target surface.The average particle velocity across the jet is reduced by approximately one third due to the damping effect of the stagnation under the conditions considered in this study.展开更多
The abrasive waterjet (AWJ) is now widely used in the advanced cutting processes of polymers,metals,glass,ceramics and composite materials like thin multiple-layered material (TMM).Various research and development eff...The abrasive waterjet (AWJ) is now widely used in the advanced cutting processes of polymers,metals,glass,ceramics and composite materials like thin multiple-layered material (TMM).Various research and development efforts have recently been made to understand the science of AWJ.However,the interaction mechanism between a workpiece and high-velocity abrasive particles still remains a complicated problem.In this work,the material removal mechanisms of AWJ such as micro penetration and micro dent were experimentally investigated.In addition,a new computer simulation model considering high strain rate effect was proposed to understand the micro impact behavior of high-velocity micro-sized abrasives in AWJ cutting.展开更多
Cavity flow oscillations in the axisymmetric cavity are critical to the operating efficiency of self-excited pulsed waterjets,which are widely employed in many practical applications.In this study,the behaviors of a t...Cavity flow oscillations in the axisymmetric cavity are critical to the operating efficiency of self-excited pulsed waterjets,which are widely employed in many practical applications.In this study,the behaviors of a turbulent flow in axisymmetric cavities causing cavity flow oscillations are investigated based on wall pressure characteristics.Experiments are performed using four Helmholtz nozzles with varying length-to-radius ratios at flow velocities of 20–80 m/s.Three orders of hydrodynamic modes in axisymmetric cavity are obtained through the spectral analysis of wall pressure.Based on the experimental results,the empirical coefficient of Rossiter’s formula is modified,and the values of the parameter phase lag and the ratio of convection velocity to free stream velocity are obtained as 0.061 and 0.511,respectively.In addition,the spectral peak with a relatively constant frequency shows that the flow-acoustic resonance is excited significantly.A modified model is introduced based on the fluidic networks to predict the lockon frequency.The results obtained can provide a basis for the structural optimization of the nozzle to improve the performance of self-excited pulsed waterjets.展开更多
Abrasive waterjet (AWJ) cutting technology has been used extensively for the cutting and processing of almost all engineering materials because of its precise cutting technique and the lack of damage caused. Currently...Abrasive waterjet (AWJ) cutting technology has been used extensively for the cutting and processing of almost all engineering materials because of its precise cutting technique and the lack of damage caused. Currently, the use of abrasive waterjet cutting in the natural stone industry is increasing. However, the effectiveness of abrasive waterjet cutting of natural stones is dependent on the rock properties and machine operating parameters. Consequently, this paper presents the influence of abrasive waterjet machining parameters on the surface texture quality of Carrara marble. The results have shown that the abrasive waterjet cutting process offers better cut surface texture quality of Carrara marble under certain parameter conditions as well as being more environmentally-friendly. The stand-off distance shows the opposite effect on both surface roughness and waviness. With a view to reducing the machining costs, every user tries to select the traverse rate of the cutting head to be as high as possible, but results show that increasing the traverse rate always causes a corresponding increase in terms of inaccuracy, surface roughness, Ra ≈ 93.7 μm, and waviness, Wa ≈ 92.6 μm. The abrasive mass flow rate is not a significant parameter during the cutting process. In all investigations, it was found that the machined surface of the marble is smoother near the jet entrance, Ra ≈ 4 μm, and waviness, Wa ≈ 5 μm, and increasingly becomes rougher towards the jet exit. The result also shows that the micro-hardness value of the Carrara marble was in the range of 122 HV to 124 HV.展开更多
In order to improve the efficiency of gas drainage before and during longwall extraction,a waterjet rotary cutting system has been developed for in-seam cross panel methane drainage.The purpose of the water rotary cut...In order to improve the efficiency of gas drainage before and during longwall extraction,a waterjet rotary cutting system has been developed for in-seam cross panel methane drainage.The purpose of the water rotary cutting system developed was to create artificial fractures along the gas drainage boreholes.During the design of the system,it was perceived that the nozzle geometry is one of the key factors,affecting cutting capacity.Therefore,we studied the structural and geometric parameters of the nozzle and optimized its performance during laboratory tests and numerical simulation.Underground trials conducted in a coal mine,indicate that production of gas drainage before and after cutting significantly increased by up to three times.The advantages of waterjet assisted gas drainage method has been identified as:1) increasing gas drainage efficiency,2) a possible development of a gas drainage fractured network within coal seams associated with panel extraction,and 3) reducing the risk of exceeding gas limits during longwalling.展开更多
This paper presented a method to create artificial fractures along the existing gas drainage borehole and increase the permeability of the coalbed using a high pressure waterjet cutting system.The field work conducted...This paper presented a method to create artificial fractures along the existing gas drainage borehole and increase the permeability of the coalbed using a high pressure waterjet cutting system.The field work conducted in Rujigou Colliery, Shenhua Ningxia Coal Group demonstrate that the coalbed permeability is increased, and accordingly, gas drainage efficiency is improved up to 3 to 6 times over the traditional methods using high pressure waterjet technique.Also, based on the monitoring data, the conceptual model for gas drainage process associated with different mining activities has been proposed, and few major advantages using waterjet assistance method have been identified.展开更多
The cleaning parameters affecting cleaning rate using pure waterjets to clean road surface was researched. A mathematical model for predicting cleaning rate was established using fuzzy mathematical method. A fuzzy rul...The cleaning parameters affecting cleaning rate using pure waterjets to clean road surface was researched. A mathematical model for predicting cleaning rate was established using fuzzy mathematical method. A fuzzy rule base character-izing the relationship between input and output parameters was built through experiments. The prediction of cleaning rate was achieved under the condition of given input parameters by rule-based fuzzy reasoning. The prediction results were analyzed through experimental verification.展开更多
Submerged abrasive waterjet peening(SAWJP)is an effective anti-fatigue manufacturing technology that is widely used to strengthen aeroengine components.This study investigated the correlation of SAWJP process paramete...Submerged abrasive waterjet peening(SAWJP)is an effective anti-fatigue manufacturing technology that is widely used to strengthen aeroengine components.This study investigated the correlation of SAWJP process parameters on surface integrity and fatigue life of titanium alloy TA19.SAWJP with different water pressures and standoff distances(SoDs)was conducted on the TA19 specimens.The surface integrity of the specimens before and after SAWJP with different process parameters was experimentally studied,including microstructure,surface roughness,microhardness,and compressive residual stress(CRS).Finally,fatigue tests of the specimens before and after SAWJP treatment with different process parameters were carried out at room temperature.The results highlighted that the fatigue life of the TA19 specimen can be increased by 5.46,5.98,and 6.28 times under relatively optimal process parameters,which is mainly due to the improved surface integrity of the specimen after SAWJP treatment.However,the fatigue life of specimens treated with improper process parameters is decreased by 0.55 to 0.69 times owing to the terrible surface roughness caused by the material erosion.This work verifies that SAWJP can effectively improve the surface integrity and fatigue life of workpieces,and reveals the relationship between process parameters,surface integrity,and fatigue life,which provides support for the promotion of SAWJP in the manufacturing fields.展开更多
Abrasive waterjet(AWJ)is widely applied in 2D machining as it offers high machining efficiency and low machining cost.However,machining a 3D surface,especially for a small curvature radius freeform surface(SCRFS),resu...Abrasive waterjet(AWJ)is widely applied in 2D machining as it offers high machining efficiency and low machining cost.However,machining a 3D surface,especially for a small curvature radius freeform surface(SCRFS),results in over-erosion of the corner,and has been one of the greatest issues of AWJ.To solve this problem,a local smoothing algorithm for SCRFS is developed by the junction of two linear segments at the corner by inserting cubic second-order B-spline to smooth the nozzle path and posture under the setting tolerance error,which is aimed to avoid over-erosion due to the change in dwell time.Analytical solutions of the smooth corner position and orientation of the nozzle path are obtained by evaluating a synchronization algorithm.According to the set tolerance error of the nozzle position and orientation,the interpolation of the smooth path of the corner meets the constraint conditions of the linear feed drive.Path simulation and experimental results show that the proposed method is validated by the experimental results and has been applied to the integral blisk machining of an aero-engine.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. 52175245 and 52274093)the Natural Science Foundation of Hubei Province (No. 2021CFB462)。
文摘To improve the rock breaking ability, cavitating waterjet and abrasive waterjet are combined by using a coaxial low-speed waterjet generated around the periphery of a high-speed abrasive waterjet, and a new type of waterjet called unsubmerged cavitating abrasive waterjet(UCAWJ) is thus produced. The rock breaking performance of UCAWJ was compared with submerged cavitating abrasive waterjet(SCAWJ)and unsubmerged abrasive waterjet(UAWJ) by impinging sandstone specimens. Moreover, the effects of jet pressure, standoff distance, abrasive flow rate and concentration were studied by evaluating the specific energy consumption, and the area, depth, and mass loss of the eroded specimen. The results show that the artificially generated submerged environment in UCAWJ is able to enhance the rock breaking performance under the same operating parameters. Furthermore, the rock breaking performance of UCAWJ is much better at higher jet pressures and smaller standoff distances when compared with UAWJ. The greatest rock breaking ability of UCAWJ appears at jet pressure of 50 MPa and standoff distance of 32 mm, with the mass loss of sandstone increased by 370.6% and the energy dissipation decreased by 75.8%. In addition, under the experimental conditions the optimal abrasive flow rate and concentration are 76.5 m L/min and 3%, respectively.
文摘This paper deals with an assessment of the machined surface created by abrasive waterjet technology regarding its cutting performance versus profile, lagging and waterjet angle assessments. The results of the experiments presented in this study are with regard to Carrara marble. The machined surfaces were measured in seven different locations across a 40 mm depth of cut by a high precision contact-type profilometer and thus assessed using the standardized amplitude parameters of the profile distribution. The lagging and waterjet angle were also evaluated by creating a digital photo of the machined surface together with a reference gauge. The existence of machining marks on the machined surface has been mostly noticeable in the bottom zone around ~20 mm depth of cut down to jet exit. This investigation leads to a conclusion that, stand-off distance and traverse rate play the roles of the utmost importance in considerations of the machined surface quality in contrast to abrasive mass flow rate. In addition, while the striation zone (rough surface) cannot be eliminated entirely, by selecting proper process parameters, a smooth cutting machined surface can be accomplished.
基金supported by Shandong Provincial Natural Science Foundation of China (Grant No. Y2007A07)
文摘In dealing with abrasive waterjet machining(AWJM) simulation,most literatures apply finite element method(FEM) to build pure waterjet models or single abrasive particle erosion models.To overcome the mesh distortion caused by large deformation using FEM and to consider the effects of both water and abrasive,the smoothed particle hydrodynamics(SPH) coupled FEM modeling for AWJM simulation is presented,in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FEM.The two parts interact through contact algorithm.Utilizing this model,abrasive waterjet with high velocity penetrating the target materials is simulated and the mechanism of erosion is depicted.The relationships between the depth of penetration and jet parameters,including water pressure and traverse speed,etc,are analyzed based on the simulation.The simulation results agree well with the existed experimental data.The mixing multi-materials SPH particles,which contain abrasive and water,are adopted by means of the randomized algorithm and material model for the abrasive is presented.The study will not only provide a new powerful tool for the simulation of abrasive waterjet machining,but also be beneficial to understand its cutting mechanism and optimize the operating parameters.
文摘A study is carried out which analyzes the machinability of polymer matrix composites under an abrasive waterjet (AWJ) and the associated erosive process or mechanism. It shows that AWJ cutting can produce good quality kerf at high production rate if the cutting parameters are properly selected. A scanning electron microscopy (SEM) analysis of the cut surfaces reveals that the erosive process for the matrix material (resin) involves shearing and ploughing as well as intergranular cracking, while shearing is a dominant process for cutting the fibres in the upper cutting region but the fibers are mostly pulled out in the lower region.
基金Supported by National Key Basic Research Program of China(973 Program,Grant No.2014CB239203)National Natural Science Foundation of China(Grant No.51474158)China Scholarship Council(Grant No.201406270047)
文摘The current research on self-resonating cavitating waterjet(SRCW) mainly focuses on the generation mechanism and structure optimization.Researches relating to the influences of disturbances at nozzle inlet on the characteristics of the jet are rarely available.In order to further improve the performance of SRCW,effects of area discontinuity(enlargement and contraction) are experimentally investigated using three organ-pipe nozzles.Axial pressure oscillation peak and amplitude as well as aggressive erosion intensity of the jet are used to evaluate the effects.The results reveal that area enlargement and contraction affect the peak differently,depending on the inlet pressure,nozzle geometry,and standoff distance;while area contraction always improves the amplitude regardless of these factors.At inlet pressures of 10 MPa and 20 MPa,area discontinuity improves the peak at almost all the testing standoff distances,while this only happens at smaller standoff distances with the inlet pressure increased to 30 MPa.The capability of area discontinuity for improving the amplitude is enhancing with increasing inlet pressure.Moreover,the cavitation erosion ability of the jet can be largely enhanced around the optimum standoff distance,depending on the type of area discontinuity and nozzle geometry.A preliminary analysis of the influence of area discontinuity on the disturbance waves in the flow is also performed.The proposed research provides a new method for effectively enhancing the performance of SRCW.
基金financially supported by the National Science and Technology Major Project(Nos.2017 ZX05009-003&2016 ZX05028)PetroChina Innovation Foundation(No.2018D-5007-0308)
文摘Abrasive waterjet(AWJ)fracturing has become an accepted horizontal multistage stimulation technique due to its flexibility and high efficiency of extensive fracture placement.The downhole tool failure of AWJ fracturing becomes an issue in the massive hydraulic fracturing because of high velocity and proppant erosion.This paper proposed a 3D computational fluid dynamics(CFD)-based erosion model by considering high-velocity waterjet impact,proppant shear erosion,and specific inner structure of hydra-jet tool body.The discrete phase approach was used to track the proppant transport and its concentration distribution.Field observation provides strong evidence of erosion patterns and mechanisms obtained from CFD simulation.The results show that the erosion rate has a space dependence in the inner wall of the tool body.The severe erosion areas are primarily located at the entries of the nozzle.Evident erosion patterns are found including a‘Rabbit’s ear’erosion at the upper-layer nozzles and a half bottom loop erosion at the lower-layer nozzles.Erosion mechanisms attribute to high flow velocity at the entry of nozzles and the inertia force of proppant.Sensitivity analysis demonstrates that the pumping rate is a primary factor contributing to erosion intensity.
基金supported by the Missouri University of Science and Technology/Waterjet Laboratory and funded by the China Postdoctoral Science Foundation(Grant No.2014M552555XB)Doctoral Program in Xi’an University of Science and Technology(Grant No.2013QDJ039).
文摘Comminution of coal to ultrafine sizes by high-pressure waterjet provides a novel method for preparation of coal-water fuels for next generation,near-zero emission electric power generation.The particle size distribution(PSD)of ground coal is a key parameter in the preparation of slurries as it determines the settling behavior of the particles and viscosity of the coal-water mixture.There are several methods available for representation and evaluation of particle size analysis data.However,fractal theory provides a means by which the entire PSD of comminuted materials can be quantified by using of a specific and exact value.In this paper,a volume-based fractal model was deduced to characterize the PSD of the coal which is ground in a specially designed comminution cell.During the size reduction process,the inlet pressures up to 276 MPa were used.
文摘The fabrication of miniature structures on components with high-integrity surface quality represents one of the cutting edge technologies in the 21st century.The materials used to construct such small structures are often difficult-to-machine.Many other readily available technologies either cannot realise necessary precision or are costly.Abrasive waterjet(AWJ)is a favourable technology for the machining of difficult-to-machine materials.However,this technology is generally aimed at large stock removal.A reduction in the scale of this technology is an attractive avenue for meeting the pressing need of industry in the production of damage-free micro features.This paper reviews some of the work that has been undertaken at UNSW Sydney about the development of such an AWJ technology,focusing on the system design currently employed to generate a micro abrasive jet,the erosion mechanisms associated with processing some typical brittle materials of both single-and two-phased.Processing models based on the findings are also presented.The review concludes on the viability of the technology and the prevailing trend in its development.
基金The project was financially supported by the Australian Research Council(ARC)under the Discovery-Projects scheme.K T would like to thank the Royal Thai Government for providing a PhD scholarship for this study.
文摘A computational fluid dynamics(CFD)study of the impact characteristics and stagnation formation on a solid target surface by an abrasive waterjet at supersonic velocities is presented to understand the impact process.A CFD model is developed and verified by experimental water and particle velocities and then used to simulate the jet impact process.The trends of the stagnation formation and its effect on the jet flow with respect to the jetting and impacting parameters are amply discussed.It is found that stagnation formation at the impact site increases with an increase in the impact time,nozzle standoff distance and nozzle diameter,while the initial peak velocity at the nozzle exit has little effect on the size of the stagnation zone.It is shown that stagnation markedly changes the water and particle flow direction,so that the particle impact angle is varied and the jet impact area is enlarged.The jet structure may be classified to have a free jet flow region,a jet deflection region with a stagnation zone and a wall jet region.Furthermore,the stagnation affects significantly the waterjet and particle energy transferred to the target surface.The average particle velocity across the jet is reduced by approximately one third due to the damping effect of the stagnation under the conditions considered in this study.
文摘The abrasive waterjet (AWJ) is now widely used in the advanced cutting processes of polymers,metals,glass,ceramics and composite materials like thin multiple-layered material (TMM).Various research and development efforts have recently been made to understand the science of AWJ.However,the interaction mechanism between a workpiece and high-velocity abrasive particles still remains a complicated problem.In this work,the material removal mechanisms of AWJ such as micro penetration and micro dent were experimentally investigated.In addition,a new computer simulation model considering high strain rate effect was proposed to understand the micro impact behavior of high-velocity micro-sized abrasives in AWJ cutting.
基金National Natural Science Foundation of China(Grant Nos.52175245,51805188)Fundamental Research Funds for the Central Universities of China(Grant No.2042020kf0001)National Key Research and Development Program of China(Grant No.2018YFC0808401).
文摘Cavity flow oscillations in the axisymmetric cavity are critical to the operating efficiency of self-excited pulsed waterjets,which are widely employed in many practical applications.In this study,the behaviors of a turbulent flow in axisymmetric cavities causing cavity flow oscillations are investigated based on wall pressure characteristics.Experiments are performed using four Helmholtz nozzles with varying length-to-radius ratios at flow velocities of 20–80 m/s.Three orders of hydrodynamic modes in axisymmetric cavity are obtained through the spectral analysis of wall pressure.Based on the experimental results,the empirical coefficient of Rossiter’s formula is modified,and the values of the parameter phase lag and the ratio of convection velocity to free stream velocity are obtained as 0.061 and 0.511,respectively.In addition,the spectral peak with a relatively constant frequency shows that the flow-acoustic resonance is excited significantly.A modified model is introduced based on the fluidic networks to predict the lockon frequency.The results obtained can provide a basis for the structural optimization of the nozzle to improve the performance of self-excited pulsed waterjets.
文摘Abrasive waterjet (AWJ) cutting technology has been used extensively for the cutting and processing of almost all engineering materials because of its precise cutting technique and the lack of damage caused. Currently, the use of abrasive waterjet cutting in the natural stone industry is increasing. However, the effectiveness of abrasive waterjet cutting of natural stones is dependent on the rock properties and machine operating parameters. Consequently, this paper presents the influence of abrasive waterjet machining parameters on the surface texture quality of Carrara marble. The results have shown that the abrasive waterjet cutting process offers better cut surface texture quality of Carrara marble under certain parameter conditions as well as being more environmentally-friendly. The stand-off distance shows the opposite effect on both surface roughness and waviness. With a view to reducing the machining costs, every user tries to select the traverse rate of the cutting head to be as high as possible, but results show that increasing the traverse rate always causes a corresponding increase in terms of inaccuracy, surface roughness, Ra ≈ 93.7 μm, and waviness, Wa ≈ 92.6 μm. The abrasive mass flow rate is not a significant parameter during the cutting process. In all investigations, it was found that the machined surface of the marble is smoother near the jet entrance, Ra ≈ 4 μm, and waviness, Wa ≈ 5 μm, and increasingly becomes rougher towards the jet exit. The result also shows that the micro-hardness value of the Carrara marble was in the range of 122 HV to 124 HV.
基金support provided by the Shenhua Ningxia Coal Group Without this assistance,the project would have been difficult to carry out.
文摘In order to improve the efficiency of gas drainage before and during longwall extraction,a waterjet rotary cutting system has been developed for in-seam cross panel methane drainage.The purpose of the water rotary cutting system developed was to create artificial fractures along the gas drainage boreholes.During the design of the system,it was perceived that the nozzle geometry is one of the key factors,affecting cutting capacity.Therefore,we studied the structural and geometric parameters of the nozzle and optimized its performance during laboratory tests and numerical simulation.Underground trials conducted in a coal mine,indicate that production of gas drainage before and after cutting significantly increased by up to three times.The advantages of waterjet assisted gas drainage method has been identified as:1) increasing gas drainage efficiency,2) a possible development of a gas drainage fractured network within coal seams associated with panel extraction,and 3) reducing the risk of exceeding gas limits during longwalling.
文摘This paper presented a method to create artificial fractures along the existing gas drainage borehole and increase the permeability of the coalbed using a high pressure waterjet cutting system.The field work conducted in Rujigou Colliery, Shenhua Ningxia Coal Group demonstrate that the coalbed permeability is increased, and accordingly, gas drainage efficiency is improved up to 3 to 6 times over the traditional methods using high pressure waterjet technique.Also, based on the monitoring data, the conceptual model for gas drainage process associated with different mining activities has been proposed, and few major advantages using waterjet assistance method have been identified.
文摘The cleaning parameters affecting cleaning rate using pure waterjets to clean road surface was researched. A mathematical model for predicting cleaning rate was established using fuzzy mathematical method. A fuzzy rule base character-izing the relationship between input and output parameters was built through experiments. The prediction of cleaning rate was achieved under the condition of given input parameters by rule-based fuzzy reasoning. The prediction results were analyzed through experimental verification.
基金supported financially by the National Natural Science Foundation of China(Nos.52275148 and U21B2077)Natural Science Foundation of Shanghai(20ZR1415300)+1 种基金Innovation Program of Shanghai Municipal Education Commission(2019-01-07-00-02-E00068)Innovation Program Phase II of AECC Commercial Aircraft Engine Co.Ltd.(Grant No.HT-3RJC1053-2020)。
文摘Submerged abrasive waterjet peening(SAWJP)is an effective anti-fatigue manufacturing technology that is widely used to strengthen aeroengine components.This study investigated the correlation of SAWJP process parameters on surface integrity and fatigue life of titanium alloy TA19.SAWJP with different water pressures and standoff distances(SoDs)was conducted on the TA19 specimens.The surface integrity of the specimens before and after SAWJP with different process parameters was experimentally studied,including microstructure,surface roughness,microhardness,and compressive residual stress(CRS).Finally,fatigue tests of the specimens before and after SAWJP treatment with different process parameters were carried out at room temperature.The results highlighted that the fatigue life of the TA19 specimen can be increased by 5.46,5.98,and 6.28 times under relatively optimal process parameters,which is mainly due to the improved surface integrity of the specimen after SAWJP treatment.However,the fatigue life of specimens treated with improper process parameters is decreased by 0.55 to 0.69 times owing to the terrible surface roughness caused by the material erosion.This work verifies that SAWJP can effectively improve the surface integrity and fatigue life of workpieces,and reveals the relationship between process parameters,surface integrity,and fatigue life,which provides support for the promotion of SAWJP in the manufacturing fields.
基金supported by NSFC-Liaoning Joint Fund(Grant Nos.U1708256,U1908232)Fundamental Research Funds for the Central Universities(Grant No.DUT18GF104)Joint Fund of MOE and GAD(Grant No.6141A02022133).
文摘Abrasive waterjet(AWJ)is widely applied in 2D machining as it offers high machining efficiency and low machining cost.However,machining a 3D surface,especially for a small curvature radius freeform surface(SCRFS),results in over-erosion of the corner,and has been one of the greatest issues of AWJ.To solve this problem,a local smoothing algorithm for SCRFS is developed by the junction of two linear segments at the corner by inserting cubic second-order B-spline to smooth the nozzle path and posture under the setting tolerance error,which is aimed to avoid over-erosion due to the change in dwell time.Analytical solutions of the smooth corner position and orientation of the nozzle path are obtained by evaluating a synchronization algorithm.According to the set tolerance error of the nozzle position and orientation,the interpolation of the smooth path of the corner meets the constraint conditions of the linear feed drive.Path simulation and experimental results show that the proposed method is validated by the experimental results and has been applied to the integral blisk machining of an aero-engine.