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Submerged jets have a variety of practical applications due to their versatility in providing efficient and environmentally friendly options for treatment in various industries. The physical background is based on the continuous water jet (CWJ) application powered via stagnation pressure. However, it is known that impact pressure is much more effective than static pressure. When the impact pressure is repeated with a high frequency per time unit, the erosive effects of water can be used even at pressures below 100 MPa, which is attractive from the point of view of the low demands of the hydraulic system. Surface modification utilising impact pressure can be achieved by employing the pulsed water jet (PWJ) method. The combination of parameters such as the traverse speed and trajectory pattern can control the number of water clusters impacting the material surface. So far, the field of application of PWJ for surface treatment has mostly been investigated water atmospheric conditions. This article focuses on the possibility of the surface modification of AISI 304L stainless steel using the PWJ method under submerged conditions. The results are compared to those obtained under atmospheric conditions. The reference samples were treated by the same technological conditions using a continuous water jet (CWJ). The affected surfaces were characterised using areal surface roughness parameters Sa, Sz, Sp, and Sv, and the surface topography and mechanism of erosion wear were evaluated by scanning electron microscopy. A significant increase in all roughness parameters was confirmed using the PWJ compared to the CWJ method (both in atmospheric and submerged conditions), which confirms the importance of using impact pressure. The surface treatment by PWJ under submerged conditions resulted in a decrease of the surface roughness parameter Sa by approximately 97% compared to atmospheric conditions at a traverse speed of 2 mm/s for perpendicular interleaved trajectory, nevertheless, the homogeneity of treatment over a larger area was improved. [ABSTRACT FROM AUTHOR]

The study of bone cement disintegration is important for advancing orthopedic and trauma surgery outcomes. Bone cement, commonly used in joint replacement procedures, plays a vital role in fixation implants. However, the long-term stability and integrity of bone cement are critical for the success of these procedures. This study focuses on the use of ultrasonic pulsating water jet technology for the selective removal of bone cement, aiming to provide a precise and efficient method for revision surgeries. The disintegration efficiency is measured in terms of depth, width and volume of the disintegrated bone cement as a result of variations in the nozzle geometry, supply pressure and traverse speed. Two different nozzle types, the standard nozzle insert and nozzle with an extension tube of 100 mm having a diameter of 0.3 mm, are used. Two supply pressure levels were taken as 10 and 20 MPa with five levels of traverse speeds as 0.5, 1, 1.5, 2 and 2.5 mm/s. The results showed an increased disintegration efficiency for all experimental conditions using an extension tube nozzle as compared to a standard nozzle (20 - 25% in terms of disintegration volume). Also, the disintegration efficiency increased with higher pressure level values (8.2 mm3 and 4.85 mm3 for p = 20 and 10 MPa, respectively) and lower traverse speed values. The results showed a promising direction in terms of the utilization of an ultrasonic pulsating jet with a modified nozzle type for higher bone cement disintegration efficiency. [ABSTRACT FROM AUTHOR]

The article focuses on easily adjustable technological parameters controlling the effectiveness of pulsating water jet (PWJ). The first technological parameter is standoff distance; this parameter controls water cluster development and should be set optimal according to process hydraulic parameters. The second parameter is feedrate, this parameter, when considering linear trajectory, controls the impact distribution on the treated area. Four hydraulic pressure levels (30, 40, 50, and 60 MPa) were selected for the experiment. The standoff distance was during the experimental runs ranging from 26 to 68 mm with the goal of finding optimal value. The optimal standoff distance was selected based on Rz and Rv parameters. Rz and Rv values show increasing tendency with increment of standoff distance followed by culmination and then decreasing tendency. The impact distribution ranged from 8 000 to 40 000 impacts per millimeter. The decrease in water impact shows strictly decreasing tendencies in all evaluated parameters. However, the increase in pressure level shows better percentual retainment of erosion effectivity during the lowering of water impact distribution. [ABSTRACT FROM AUTHOR]

Erosion of solids by liquid droplets is a phenomenon which is a compromise between mechanical properties of the material and droplet hydrodynamic parameters. While a number of studies deal with the deformation of drops, the deformation evolution inside the material has not yet been revealed, mainly from the point of view of the time action of the impinging drops The mechanical response of AISI 316L was investigated under gradually increasing numbers of impingements of liquid droplets, with a droplet volume of Vd ≅ 0.9 mm3, generated by an ultrasonic pulsating water jet with the frequency f = 40 kHz from 1 to 20 s. The surface roughness and the wear rates were determined using a laser profilometer. The cross-section of the selected samples was subjected to microhardness measurement with a load of 0.150 N in a 2D grid, which included the entire perimeter of the deformed area. The minimal microhardness measurement grid under the groove had dimensions of 15 × 15 indents, equal to an area of approximately 450 × 600 µm. A maximum hardness increase was observed at the lowest measured depth of 30 µm. An increase in hardness was observed at 300 µm below the surface. The hardening in the deeper subsurface area was most likely caused by shear stress. This shows the high degree of similitude between the solid and liquid droplet impingements. The results indicate that the currently accepted theory on the development of erosion over time has shortcomings, as demonstrated in this work by the ratio between the utilised droplet diameter and the grain size of the material.

Surfaces created by the erosive action of water droplets have not been sufficiently explored because of their stochastic structure, which depends on hydraulic parameters. This article details the complex analysis of surfaces created by the controlled distribution of water droplets on the surface of AISI 304L using an ultrasonically stimulated water jet. The traverse speed of the jet controlled the distribution of the water droplets. The surface topology was modified in an interleaved mode when the trajectories were parallel for all samples. Additionally, the second layer treated the other half of the preprepared samples with a perpendicular trajectory with respect to the parallel trajectory. The 3D surface reconstruction was performed using a noncontact MicroProf FRT measuring instrument. Several profile roughness parameters (Ra, Rz, Rv, Rp, Rsk, and Rku), areal surface roughness parameters (Sa, Sz, Sp, Sv, Ssk, Sku, Sdr, Sk, Spk, and Svk) and surface isotropy values were measured for the surfaces generated using variations in the traverse speed of the jet. The measurement results show a decreasing trend of surface roughness upon an increase in the traverse speed, and a better surface finish was also measured for the cross-hatch trajectory compared to the linear trajectory. The results also show that the generated surfaces have deeper valleys with truncated peaks, which are suitable for use in a wide range of technical and medical applications. This study shows the potential utilization of controlled liquid droplet impingement for surface preparation in various application domains.

There are many technological ways to activate biocompatible surfaces, but in some cases, there are not reliable for elderly patients. It has been found that surfaces created using pulsating water jets have a structure similar to trabecular bone structures. Such a similar shape to the endoprosthesis stems would enable faster fixation. The paper presents a novel way of utilizing the water hammer effect caused by forced multiple droplet impingement with a spatial frequency of 40,000 i/s on Ti6Al4V titanium alloy surface under different technological conditions. The objective was to create a structured surface with desired values of surface profile parameters Ra and Rz to increase the possible potential for implant osseointegration, fixation and stability. Pulsating water jet was generated at pressures from 20 to 100 MPa using a circular nozzle with a diameter of 1.32 mm. Two different strategies of the jet trajectory, namely linear and cross-hatch strategy, were investigated. Results were compared with grit blasted followed by plasma spray-coated femoral stem for cementless total hip arthroplasty. It has been found that variation in the input parameters results in significant changes in the surface generated. Samples whose surfaces were generated using energy intensity lower than 5 KJ/mm2 and have surface roughness in the range Ra = 4 – 8 μm were selected for surface topography and morphology analysis along with the commercial femoral stem. SEM analysis revealed the absence of foreign contamination and steeper surface heights on pulsating water jet treated samples compared to standard femoral prosthetic. The cross-section images showed the presence of sub-surface voids and craters of different sizes due to the jet's action. Surface topology is similar to trabecular shape. This indicates that roughening the surface increases the surface area and thus has potential bone tissue ingrowth during osseointegration. [ABSTRACT FROM AUTHOR]

The local residual stresses (tensile) generated on the surface of a component during its manufacturing (machining, welding) cause deterioration of its service life. To eliminate the negative effect of the stresses, the surface is treated using different methods (shot peening, laser shock peening, heat treatment, water jet peening). The application of ultrasonic technology to modify the continuous jet has been intensively researched for treating advanced stages of erosion. In this work, the modifications in the mechanical properties (tensile strength, micro-hardness and residual stress measurements) of AISI 304 Tungsten inert gas welded joints were investigated after ultrasonic pulsating water jet treatment in the incubation stage of erosion. This revealed that the initial tensile residual stress in the welded joints was converted to compressive stress after the treatment. The micro-hardness of the joints after the treatment increased about 40% in the heat affected zone in the near-surface region. Also, the tensile properties increased by about 37.8% and 34.6% in yield strength and ultimate strength, respectively. The microstructural examination of the near-surface region showed the grain reformation mechanism. [ABSTRACT FROM AUTHOR]

Ultrasonic pulsating water jet for non-thermal and selective removal of acrylic bone cement is studied. Variation of acoustic chamber length is used for tuning of the ultrasonic system into the resonance regime to gain maximum power transmission. The study investigates the minimal technological conditions such as nozzle traverse speed and supply water pressure required to generate disintegration grooves in bone cement mantle. It also proposes the safe standoff distance range, which is essential for its potential application during the extraction of bone cement without compromising host bone. Palacos R+G bone cement was used for the experiments. Generated groove depths were measured using MicroProf FRT and analyzed using SPIP software. Depth values showed an increasing trend with an increase in acoustic chamber length, decrease in traverse speed, and increase in supply pressure values. From the entire experimental domain, a maximum depth of 615 μm was obtained at 22-mm chamber length, 0.5-mm/s traverse speed, 10-MPa pressure, and a standoff distance of 4 mm. Brittle fractured surface features like material chipping, micro-pits, cracks, and sheared material layers were observed in the SEM images. Disintegrated debris, diameter 21–37 μm, conceived from pit diameters can be used to design a suction unit. Real-time control of the disintegration process using accelerometer sensors was shown. The results support the idea of using pulsating water jet for bone cement removal in a single blind hole. Minimal technological parameters reduce reaction force of the hand tool, allowing bone cement removal without bone fracture or perforation. [ABSTRACT FROM AUTHOR]

Pulsating water jet technology for rock erosion application has been emphasized in this study. The erosion phenomena are explored as an eroded depth, eroded width and volume eroded of the sandstone at frequency f = 20,000–40,000 Hz by using pulsed water jet. The surface was eroded at pressure 20–40 MPa; standoff distance 20 mm; nozzle diameter 1.6 mm; and feed rate of the jet 125–200 mm/s. The eroded depth, eroded width, and volume of the eroded sections were evaluated through non-contact-type optical profilometer. The result shows the relationship between feed rate of the jet, pressure, and standoff distance, which affects the erosion depth and width and volume removal. At f = 40,000 Hz, the maximum value of erosion depth, width, and volume removal was obtained. The microstructural analysis Field Emission Scanning Electron Microscopy (FESEM) examined the erosion topography, plastic deformation, and failure analysis at a frequency f = 20,000–40,000 Hz. The results reveal that the frequency change affects the erosion, and failure was observed at 40,000 Hz. This is the result of the deeper and narrow eroded surface caused by the enhanced number of impacts (200–320 impact per mm) and concentrated stream of a jet at 40,000 Hz. [ABSTRACT FROM AUTHOR]

This article deals with the manifestations of erosion of statically acting concentrated multiple droplet impingements on materials over different lengths of time in order to assess the erosion evolution when the materials are submerged, as compared with the action of droplets on the materials under atmospheric conditions. The study aims to determine the extent of the erosive effects of droplets in underwater conditions. Experiments were conducted in a plastic pool in which the water level was varied from h = 80 to h = 120 mm to identify the effect of hydrostatic pressure at p 120 = 0.1025 MPa and p 80 = 0.1021 MPa. The results were compared with that of a control group of samples obtained under atmospheric air conditions. To observe the erosive damage evolution, 15 (n = 5) sites on the ductile materials EN AW-Al 99.5 and CW004A were exposed to high-intensity droplet impingement at defined exposure times. The exposure time varied from 0.125 s to 1.875 s, with increments of 0.125 s. As a droplet generator, an ultrasonic pulsating water jet with a frequency f = 20 kHz, a pressure p = 30 MPa and a nozzle diameter d = 0.4 mm was used to achieve the theoretical subsonic speed of the droplets. The results exceeded the assumptions regarding the possible attenuation of water pulses. It was found that under the theoretical speed of the jet v w = 225 m/s, the submerged condition causes attenuation in its erosive action. The incident area in the case of submerged treatment was more symmetrical. The erosion shift in term of prolonging incubation erosion stage was found to be a result of the increasing hydrostatic pressure. The results suggest that this method can also be used under submerged conditions for treatment or material drilling. • A low-pressure pulsating water jet under submerged conditions causes erosion. • Hydrostatic pressure influences the erosion shift. • The incident area is symmetrical under submerged conditions. [ABSTRACT FROM AUTHOR]

The article deals with the measurement of micro-hardness of the track by the action of ultrasonic excitation of pulsating water jet. The cumulative effect of liquid matter in the form of droplets concentrated in waveform measurements was provided in horizontal and vertical direction to material core (AISI 304). The material was subjected to pressures of p = 40, 50 and 60 MPa with the actuator working at a frequency of 20,14 kHz and traverse speed v = 1,1 mm/s, v = 0,80 mm/s and v = 0,30 mm/s respectively. The micro hardness measurement was carried out after machining it by pulsating water jet. The values were recorded in the zone located transversally under the trace to the depth of 1,5 mm with 0,1 mm distance between successive points. It was found that the deformation of material was ascertained from the boundary to the outer environment created by pulsating water jet to the inner core of the material. The results indicate that the pressure was the most influential parameter, which was responsible for the deformation strengthening of the material.

• Pulsating water jet (PWJ) induces local deformation on AISI 304 surface. • PWJ at 20 kHz induces stresses ranging between 287 MPa – 540 MPa. • Inhomogeneous plastic deformation is responsible for enhancing the surface integrity. Enhancement of the life of the engineering components is essential from the perspective of its performance, therefore, it is necessary to eliminate the negative effects that attenuates the life of these components. Numerous surface treatment methods are used at present out of which water jet peening process have been stated to overcome the shortcoming reported in other surface treatment methods like surface defects caused by the embedment of particles during shot peening, thermal effects caused by laser shock peening. It has been reported in studies that the technological modification of water jet technology, ultrasonically generated pulsed water jet (PWJ) can be used for the peening application but still the detailed study of parametric variations for the peening process is not clearly explained. The present work aims at reporting the effect of variation of parameters: jet pressure (40 MPa to 100 MPa), traverse speed of the nozzle (5 mm/s to 25 mm/s) and standoff distance (15 mm to 31 mm) during the ultrasonically generated PWJ peening process. The peened surface was quantified in terms of surface residual stress measurements, micro hardness and surface roughness measurements. The results indicate that the variations in the parameters shows significant changes in the surface residual stress enhancement and strengthening process. The lower pressure (40 MPa), lower traverse speed (5 mm/s) and higher standoff distance (31 mm) showed the maximum improvement in the surface residual stress (up to 540 MPa) and micro-hardness (up to 570 HV). The impact of the repeated pulses causes plastic deformation on the surface and sub-surface layers which results into the change in the microstructures of the affected area. The microstructural examination through field emission scanning electron microscopy showed variations in these deformations under different parametric conditions. This study can give better understanding for the proper selection of the peening parameters for practical applications using ultrasonically generated pulsed water jet technology. [ABSTRACT FROM AUTHOR]

Presented article is focused on the comparison of erosion efficiency on the surface treatment of ultrasonically enhanced PWJ (pulsating water jet) on different metal materials surfaces. Surfaces of EN X5CrNi18-10 stainless steel and EN-AW 6060 aluminum alloy were evaluated. Pulsating water jet technological factors were set to the following values: pressure was 70 MPa, circular nozzle diameter was 1.19 mm, traverse speed of cutting head was 100 mm s−1 (which is 200 impact for millimeter) for stainless steel and 660 mm s−1 (which is 30 impact per millimeter) for aluminum alloy. The evaluation was made based on the surface topography evaluation, evaluation of microstructure, and microhardness in the transverse cut. The results of the stainless steel surface evaluation show slight erosion of material, with creating microscopic craters. Subsurface deformation was found to a depth of a maximum of 200 μm. Hardness measurement shows 11% higher value of hardness under the affected area compared with a measurement in the center of the sample. From the findings, subsurface deformation strengthening of stainless steel with minimal influence of material surface can be assumed. Surface deformation of aluminum alloy is characterized by the formation of more pronounced depressions and less pronounced protrusions. Depressions were created by a combination of compression and tearing off material parts. A decrease in hardness value of 18% compared with a measurement in the center of the sample. In places of the first indent just below the disintegrated area (up to 600 μm deep), it is possible to assume the material plastic deformation, but the value of aluminum alloy tensile strength Rm is not exceeded. The experimental results from an aluminum alloy evaluation do not confirm the subsurface mechanical strengthening of the material. [ABSTRACT FROM AUTHOR]

This study addresses the erosion transition of an aluminium surface arising from the periodic impact of a tangentially acting pulsating water jet (PWJ) with a spatial frequency of f = 20 kHz. The erosion effect was observed as a function of the standoff distance z (mm) along an incline (from 5 mm to 90 mm) and constant trajectory (at standoff distances of z = 25 mm, 75 mm and 125 mm) at a jet pressure of 100 MPa and traverse speed v = 10 mm/s. The aim of this study is to assess the manner in which the erosion along the PWJ pathway changes the measured dynamic signal (by means of acoustic emission measurements). The effects of hydrodynamic erosion, such as elastic and plastic deformation, were observed with the aid of a scanning electron microscope and compared with time records in terms of acoustic emission (AE) recorded during impact. Moving the PWJ head and gradually changing the standoff distance along the inclined trajectory resulted in different erosion regimes. With a gradual increase in the standoff distance (from 5 mm–90 mm), the observed erosion regimes were observed in terms of micro-pitting action, crack and crater formation and material folding/upheaving. The erosion effects of a PWJ compared with those of a continuous water jet were investigated at constant standoff distances of z = 25 mm, z = 75 mm and z = 125 mm. The differences in the erosion phenomenon under different conditions were observed in terms of the material damage, crater dimensions and surface and sub-surface features. The AE recorded during the impact of the PWJ demonstrates a correlation between the ongoing erosion phenomenon and the AE signals. This relation for the encoded complex waveform (PWJ) confirms the significant information about the ongoing process in terms of material deformation and dislocation movement. • Standoff distance generates different erosion regions. • Isolated sub-surface voids were observed. • The time records clearly exhibit an increase in amplitudes whenever material disintegration-separation-tearing occurs (load above the strength limit). • The correlation between the depth profile and AW reveals the effective interaction between the dynamic signal. [ABSTRACT FROM AUTHOR]

The paper deals with the topic of the determination of erosion effects of a pulsating water jet impinging the surface of aluminium alloy samples treated by various techniques (rough and fine milling, planing and rolling). The influence of the initial surface topography on the final topography of the sample exposed to the pulsating water jet was investigated. Erosion of surface layers was analysed and discussed in relation to the traversing velocity of the jet. It was found that initial surface properties have a significant impact on the final topography. Degree of the surface erosion was determined by the measurement of the surface parameter Ra.

The residual stress and subsurface hardness of welded joints treated by peening using an ultrasonic pulsed water jet at pressures of 20–60 MPa with various traverse speeds and standoff distances were measured. The effect of the treatment was quantified by measuring the residual stress using X-ray diffraction in three regions (the welded zone, heat-affected zone, and base metal). To analyse the depth of the plastic deformation induced by the pulsating water jet, microstructural analyses and micro-hardness measurements were conducted. The surface topography of the treated samples was examined by measuring the surface roughness using a contact surface roughness profilometer. After pulsating water jet treatment, the samples showed both increased residual stress and surface roughness at pressures of 20–60 MPa. Increased subsurface hardness of the treated region was observed up to a depth of 200–250 µm at pressures of 40 and 60 MPa, deeper than that of the sample prepared at 20 MPa. The microstructural analysis identified the involved plastic deformation phenomenon occurred during the treatment process. This method of surface treatment, where the efficiency of the jet is enhanced by the generation of pulses using an acoustic generator, showed promising results for its practical application as a post-weld treatment method. [ABSTRACT FROM AUTHOR]

The present study is focused on the disintegration effect of ultrasound-enhanced pulsating water jet (PWJ) technology on brass CW614N. The first part of the study discusses the effect of a combination of factors based on the full factorial design of experiments (DoE) 33. Traverse speed v (mm s−1), circular nozzle orifice diameter d (mm), and hydraulic power Ph (kW) are selected as the disintegration variable factors. Mass material removal Δm (mg s−1) is evaluated based on the change in these variable factors. In the next part, a verification experiment is performed with by varying the traverse speed between 0.2 and 1.4 mm s−1. The mathematical model calculated in DoE is confirmed. Moreover, the significant effect of hydraulic power Ph (kW) on the efficiency of the PWJ disintegration is demonstrated. The last part of the study discusses the surface and subsurface effects on a PWJ after brass CW614A erosion. A sample disintegration with hydraulic power Ph = 13 kW and circular nozzle diameter d = 1.321 mm is observed. Optical profilometry and scanning electron microscopy are performed to visualise the surface erosion of a selected groove. A significant mass material removal is observed from the groove surface, and the disintegrated surface is characterised by erosion and crater formation. A slight cold deformation with a maximum depth of 200 μm is detected in the subsurface layer. The experiment and results present a part of an extensive research focused on describing the PWJ disintegration efficiency for metallic materials. [ABSTRACT FROM AUTHOR]

Acoustically excited pulsating water jet cutting (PWJ) is technological modification of material disintegration. From the reason of not detail described area of area of acoustically excited pulsating water jet with using circular nozzle is article focused on further research of mentioned technology. Presented article is focused on evaluation of surface integrity of copper CW004A and brass CW614N, changes in surface layer and strengthening in subsurface layer after impact of acoustically excited pulsating water jet. Surface topography was evaluated by using optical profilometry. Changes in surface layer were evaluated based on mass material removal Δ m [mg/s] and maximal depth of penetration PWJ h max [mm]. Strengthening in subsurface layer was monitored by nanoindentation measurement with Berkovich indenter. Evaluation of subsurface layers discover slight strengthening under disintegrated surface with lower elasticity. [ABSTRACT FROM AUTHOR]

Erosion effects of a pulsating water jet impinging the surface of aluminium alloy samples pre-treated by various techniques (rough and fine milling, planing and rolling) were studied. The influence of the initial surface topography on the final topography of the sample exposed to the pulsating water jet was investigated. Based on roughness parameter Ra erosion of surface layers was analysed and discussed in relation to the traversing speed of the jet. It was found that initial surface pre-treatment have a significant impact on the final topography of the surface affected subsequently by pulsating water jet. Surfaces, whose properties are significantly affected by the action of some machining processes (i.e. milling) show much greater resistance to pulsating water jet than unpaved surfaces (i.e. rolling) and surfaces have smaller roughness. While milled (rough or fine) or planed surface roughness has approximately the same increase of Ra parameter, only rolled surfaces are up to 150 times rougher after pulsating water jet treatment. This is due to the small hardening of the surface layers and reduced durability against pulsating water jet in comparison with others investigated techniques. The highest roughness was achieved on all pre-treated surfaces at the lowest speeds, because the pulsating water jet affects the surface for a longer time. [ABSTRACT FROM AUTHOR]

The erosion of 25CrMo4 (EA4T) steel was studied to determine the surface and subsurface damage due to the high-frequency impingement of water droplets using an ultrasonic droplet generator. The material under investigation is railway axle steel, where the pulsating water jet can be used as a surface treatment method to increase the fatigue resistance. The surface processing is related mainly to standoff-distance which was changed to explore the effect of pulsating water jet while the other parameters were kept constant. Surface and subsurface conditions of the material were analyzed by means of light microscopy, scanning electron microscopy and transmission electron microscopy. By altering the standoff distance, it is possible to investigate droplet impingement from the point of view of the pulsating water jet process for different purposes, such as for maximal erosion or for an increase of fatigue resistance by introduction of severe plastic deformation to the surface. The maximum erosion state was reached for a standoff distance of 35 mm when a crater depth of 750 μm and a width of 1500 μm was observed. The mild conditions, when only plastic deformation is reached occurred at a standoff distance of 21 mm. The occurrence of subsurface cavities in materials with higher hardness indicates a significant penetration ability of the periodic high-density action of water droplets at subsonic speeds. • Surface and subsurface erosion manifestations on EA4T steel were analyzed. • Microchannels due to penetration ability under the visible groove were observed. • The subsurface hardening on the sides of the groove is stochastic. [ABSTRACT FROM AUTHOR]

Presented article is focused on surface integrity evaluation of brass CW614N form the sight of surface topography, structural changes in surface layers and strengthening character in subsurface layers after impact of acoustically excited pulsating water jet (PWJ). Surface topography was evaluated using optical profilometry. Structural changes in subsurface layer were observed based on mass material removal Δm [mg/s] and maximal depth of penetrance of PWJ h max [mm]. Nano indentation measurement according to Berkovich were used to examination of strengthening character in subsurface layer. Disintegration of experimental samples was performed under constant technological conditions: hydraulic power of plunger pump P h = 19 kW; round nozzle diameter d = 1.6 mm; feed speed rate v = 0.75 mm/s; pressure of plunger pump p = 38 MPa, stand-off distance of nozzle from target material z = 45 mm; ultrasound frequency f = 20.29 kHz and as variable factor was set power of ultrasound P on values 340, 360 and 380 W. In terms of surface topography experimental investigation proved that PWJ under selected conditions is not suitable for precision machining. Evaluation of the surface characteristics indicates that the chemical composition has a significant effect on material weight loss Δm [mg/s] and a maximum depth of penetration of PWJ h max [mm]. Evaluation of characteristics of subsurface layer was observed strengthened area with lower elasticity. [ABSTRACT FROM AUTHOR]

Advanced technological aspects of cement based composites have been recently focused on developing new materials, which are high performance and exhibit high compressive strength. Using of carbon nanotubes improve microstructure and properties of cement matrix and make them promising fillers into many engineering materials. In this paper, experiments oriented at the study of dispersion of CNTs in water with respect to their use in cement compositions are described and a novel method of CNTs dispersion in water using pulsating water jets is proposed. [ABSTRACT FROM AUTHOR]

This paper deals with on the investigation of surface topography, morphology and anisotropy of copper alloys – brass and bronze, created by pulsating water jet with frequency 20.38 kHz. The material was disintegrated using more passes of a pulsating water jet using flat nozzle, at pressure 40 MPa and stand off distance z = 55 mm. The average values of Ra , Rq , Rz roughness were analyzed at changing traverse speed and number of transitions. The effect of tensile strength and material hardness as mechanical properties of material affecting the average value of the roughness has been evaluated. It is assumed that this new way of metal eroding can be used in the automotive and engineering industries in the future e.g. for surface treatment. [ABSTRACT FROM AUTHOR]

The results of an experiment focused on the visualisation of pulsating and continuous water jets are presented in this paper. Water jet technology is widely used for surface cleaning, removal of damaged material layers, preparation of surfaces, and in many other applications. The aim of the experiment was to test the applicability of the shadowgraph technique combined with PIV processing algorithms to visualise water jet structure and analyse flow velocity field. Knowledge of the geometry and velocity fields of pulsating water jets generated by a high-pressure system is necessary for the optimal tuning of the system in respect of the maximum disintegration effect on treated material. Visualisation methods also significantly contribute to the development of new pulsating systems at the design stage. The presented procedures and experimental results demonstrate the above mentioned method as an effective analytical tool for the study of water jet geometry and velocity fields. Problems related to the application of this method are also described in the paper, together with a concept of how the problems could be solved. [ABSTRACT FROM AUTHOR]

Characteristic of an ultrasonically generated pulsating water jet (PWJ) is a liquid column, the structure of which can be divided - in terms of the standoff distance of the nozzle z [mm] - into imaginary efficiency zones (initial, transition/main, final). This fact is caused by the flow gradually developing into individual pulses. The structure of the PWJ and, consequently, the nature of its interaction with the material depends on the values of technological parameters (standoff distance of the nozzle, fluid pressure, frequency of ultrasonic generation, length of the acoustic chamber, nozzle diameter, feed rate). A geometric parameter - the impact angle α [°], plays an important role, too. To date, no research has been conducted to investigate the effect of a changed impact angle of the ultrasonically generated PWJ on material erosion. Therefore, the subject matter of this study is to investigate the effect of modified impact angle of the PWJ (α = 90°, ±85°, ±75°, ±65°, ±55°, ±45°) on disintegration (groove depth h d [μm], mass loss Δm [g]) of the aluminum alloy EN AW 6060 with upward (+) and downward (−) stair motion of the nozzle over the material with the standoff distance of the nozzle ranging between z = 10–115 mm at the frequency of f s = 40 kHz, the pressure p = 40 MPa and the feed rate v = 2 mm/s. The experiment showed a semicircular pattern of grooves created in this way. The erosion rate under the perpendicular impact (α = 90°) was not the greatest due to development of a thicker protective layer of fluid. The PWJ downward motion showed greater disintegration capacity under all impact angles, probably due to the plowing effect. • Effect of the impact angle, standoff distance and direction of nozzle motion over the material on erosion was investigated. • The PWJ erosive effect mostly depends on the degree of asymmetry of the impinging fluid pulses. • Erosion under the perpendicular impact (90°) was attenuated by the formation of a thicker fluid layer. • Downward motion of the PWJ showed greater disintegration capacity, probably due to the plowing effect. • Material disintegration was observed in the form of initial and advanced stages of erosion. [ABSTRACT FROM AUTHOR]

Abstract: It is well known that the collision of a high-velocity liquid mass with a solid generates short high-pressure transients which can cause serious damage to the surface and interior of the target material. To take advantage of this fact in the high-speed water jet technology, a special method of the generation of the high-speed pulsating water jet was developed recently and tested extensively under laboratory conditions. The method is based on the generation of acoustic waves by the action of the acoustic transducer on the pressure liquid and their transmission via pressure system to the nozzle. In this paper, results of investigation of the process of interaction of the pulsating jet and the aluminium sample are presented. Aluminium samples were exposed to pulsating jets generated under various operating conditions (such as operating pressure, stand-off distance and excitation amplitude of the acoustic generator). The effects of pulsating water jet impact on the aluminium surface were studied using methods of optical microscopy and image analysis. Topography of the surface created by the action of pulsating jet and characteristics of the surface were measured by the optical surface measuring system. Based on the analysis of obtained results, likely mechanism of the aluminium surface erosion and disintegration by the action of the pulsating water jet is discussed in the paper. [Copyright &y& Elsevier]

This article deals with the analysis of the subsurface deformation effects of materials due to the periodic action of liquid droplets, each with a constant volume of approximately 36 mm3 distributed with a spatial frequency of 20,000 i/mm. Sample grooves were analyzed within standoff distances where the prevailing mechanism is acceleration culmination depletion using the stair trajectory to avoid a possible Doppler effect. Using X-ray μ-CT, a network of cavities corresponding to a fractal shape was identified below the surface. It is apparent that the ability to erode does not end with the formation of a groove but continues into the core of the material in the form of microjetting, tunneling, or piercing. From that perspective, two types of these cavities have been identified, blind and transient, with diameters of a few micrometers. The topological changes in the subsurface region of the sample were analyzed using X-ray μ-CT progressive sectioning. The anticipated subsurface deformation was further explored and analyzed using SEM analysis. The integrity of the material around the cavities was assessed according to microhardness to explain the microjetting, tunneling, and piercing propagation. The results suggest that the effect of the lateral jetting after droplet collapsing causes extensive hydrodynamic tunneling in the material that is much higher during the intense periodic action of water droplets, even at subsonic speeds. [Display omitted] • The origin of subsurface voids is clarified. • Subsurface network microcavities are identified. • Blind and transient subsurface cavities are observed. • Relative and real erosion depths are identified. • Residual water microjetting is observed to be multidirectional. [ABSTRACT FROM AUTHOR]

This study focuses on the analysis of the surface material integrity of the polished, rigid, solid surface of an aluminium alloy after periodical impingement of liquid droplets with variable volume and impact frequency distributions normal to the solid surface. The volume of water droplets was determined for the pressures of 20 and 40 MPa. By increasing the traverse speed of the ultrasonic pulsating water jet head with respect to the stationary tested specimen, the number of water droplet impacts on one area was controlled in order to reach the early erosion stages. Also, for the comparative study, aluminum alloy was exposed to continuous water jet for both supply pressure 20 and 40 MPa with traverse speed of 1 mm/s over the material surface. Systematic testing focused on material integrity in the early erosion stages in the interval between the elastically deformed surface and material disintegration was conducted with the aid of microhardness measurements, X-ray analysis of stress state, and microstructural analysis by SEM. The motivation for carrying out this experiment was to verify the effects of periodic drops on the integrity of the material and to identify the parameters leading to surface strengthening without erosion as compared to continuous jet. Such surface treatments can improve fatigue life, similarly to shot peening. • Material integrity investigation of early erosion stages with variable numbers of impingements. • Compressive stress and residual stress built up during each erosion stage. • Relationship between impingement distribution vs. hardness and surface roughness. • High intensity impingement of rigid surfaces does not increase compressive stresses. [ABSTRACT FROM AUTHOR]

The water hammer effect is the basis of technologies which is artificially responsible for the decay of continuous jets. A recently developed technique enhances the pressure fluctuations using an acoustic chamber, leading to enhanced erosion effects for various water volume flow rates. The optimum standoff distance for an ultrasonic enhanced water jet is not appropriately estimated using an inclined trajectory. The objective of this study is to comprehend the true nature of the interaction of the standoff distance following the stair trajectory and traverse speed of the nozzle on the erosion depth. Additionally, it also critically compares the new method (staircase trajectory) that obeys the variation in frequency of the impingements for defined volume flow rates with the inclined trajectory. In this study, at constant pressure (p = 70 MPa), the role of impingement distribution with the variation of traverse speed (v = 5–35 mm/s) along the centerline of the footprint was investigated. The maximum erosion depth corresponding to each traverse speed is observed at approximately same standoff distance (65 ± 5 mm) and decreases with the increment in traverse speed (h = 1042 and 47 µm at v = 5 and 35 mm/s, respectively). The results are attributed to the variation in the number of impingements per unit length. The surface and morphology analysis of the cross-section using SEM manifested the presence of erosion characteristics (micro-cracks, cavities, voids, and upheaved surface). By varying the water cluster, different impingement densities can be achieved that are suitable for technological operations such as surface peening, material disintegration, or surface roughening. [ABSTRACT FROM AUTHOR]

This study compared the effect of the interaction time of periodic water clusters on the surface integrity of AISI 304 tungsten inert gas (TIG) welded joints at different excitation frequencies, as the effect of the technological parameters of pulsating water jet (PWJ) on the mechanical properties of TIG welded joints are under-researched. The TIG welded joints were subjected to different frequencies (20 and 40 kHz) and traverse speeds (1–4 mm/s) at a water pressure of 40 MPa and a standoff distance of 70 mm. The effect of the interaction of the pulsating jet on the material and the enhancement in its mechanical properties were compared through residual stress measurements, surface roughness, and sub-surface microhardness. A maximum enhancement in the residual stress values of up to 480 MPa was observed in the heat-affected zone, along with a maximum roughness of 6.03 µm and a maximum hardness of 551 HV using a frequency of 40 kHz. The improvement in the surface characteristics of the welded joints shows the potential of utilizing pulsed water jet technology with an appropriate selection of process parameters in the treatment of welded structures. [ABSTRACT FROM AUTHOR]