Water Jet Impact Research Articles

Mechanisms of pop-up delamination in laminated composites pierced by the initial pure waterjet in abrasive waterjet machining

The entrainment abrasive waterjet machines start with a pure waterjet before abrasives are injected to avoid nozzle clogging. This pure waterjet impact is the primary cause for delamination in the form of edge pop-up of laminated composites. This paper presents an investigation into the pop-up delamination formation mechanisms. A coupled fluid–solid numerical model is developed by coupling smoothed particle hydrodynamics method and finite element method. It is found that pop-up delamination is initiated due to the material’s elastic response to a rapid release of shock pressure to stagnation pressure and the traverse shear stresses induced by the bending of the plies. A hydro wedging effect between the plies due to flow divergence propagates the delamination. There is a threshold value for the water pressure above which pop-up delamination does not increase significantly. Moreover, the smallest delamination area takes place on the [0]12 composite, followed by the [0/45/90/-45/0/45]s and [0/90]3s composites.

Flow Field Simulation and Parametric Design of High-pressure Water Jet Cutting Leather Based on Fluent

This paper studies the flow field simulation process of high-speed water jet cutting leather. Based on the water jet impact model, Fluent is used to analyze different jet pressures, spray distances and nozzles diameter. The effect of the outlet diameter on the jet impact velocity and the impact area is studied. Through the study of three factors, it is found that the jet pressure has the greatest and most direct influence on the jet velocity. Therefore, adjusting the jet pressure is an important means to successfully complete the water jet cutting. The above research has a good guiding for cutting leather.

INVESTIGATION OF WATERJET EFFLUX NOISE WITH NUMERICAL TECHNIQUES

The URN resulting from a waterjet propulsion (WJP) is to be accurately estimated for stealth considerations. Such WJP systems are designed to operate either with a submerged jet (wet transom) or with a free surface jet (dry transom). The URN due to the operation of WJP system can be broadly categorized as pump noise and nozzle efflux noise. Pump noise includes mainly the cavitation noise and the tonal mechanical/hydrodynamic noise, whereas the nozzle efflux noise is due to jet impact and bubble entrainment. The present study attempts to implement advanced numerical techniques to estimate URN due to the nozzle efflux of a WJP in both wet and dry transom modes. Large Eddy simulations (LES) are carried out to simulate the hydrodynamics of turbulent multiphase flow behind both submerged and free surface water jets. The impact of water jet on free surface and subsequent bubble generation rate is captured using multiphase volume of fluids (VOF) technique. The impact noise is estimated by directly recording the fluctuating acoustic pressure at certain field points during the simulation. A blob detection algorithm is implemented to compute the bubble generation rate. A mathematical model to compute the bubble pulsation noise from bubble generation rate is validated and implemented. The estimated URN levels in wet and dry mode are presented and compared. Key inferences are presented which could be useful in further investigation of URN from water jet of stealth vessels, as well as to investigate bubble noise from propeller cavitation, air lubrication etc.

Study on the influence of contact surface curvature on water jet impingement flow field and initial damage of coal seam

AbstractThe design of the contact surface has a big impact on how well water jets penetrate coal rock. The influence of water jets on contact surfaces with various curvatures is studied using numerical modeling to elucidate the flow field and coal seam damage characteristics. The water jet impingement flow field region can be separated into three areas: velocity concentration, divergent flow, and wall recirculation. As the jet water pressure rises, the flow field's distribution features become more apparent. Water jet impact morphology and flow field properties on contact surfaces of various curvatures are comparable. The peak velocity ratio of the wall and axis falls first, then increase as the curvature radius ratio (n) of the contact surface increases. Near n = 0.8, the peak velocity ratio of the wall and axis reaches a minimum, indicating that the kinetic energy loss in the process of water jet impact to the contact surface is the greatest. When water jets of various pressures impact the contact surface, the peak velocity drops by two‐thirds before and after impact, and nearly 89% of the kinetic energy is lost in the impact process. The range of the initial damage and failure area in the center of the contact surface and the initial damage and failure area on both sides of the wall caused by water jet impact decreases gradually as n increases. When n = 2, the initial damage and failure region on both sides of the wall has virtually vanished; when n = 0.2. The contact surface's center failure depth induced by water jet impact is the deepest. The initial injury is unaffected by changes in jet water pressure.

Application of a water jet for cleaning grease and improving the surface adhesion properties of galvanized steel wire ropes

Traditional cleaning processes may be banned in the near future because of the hazards they pose to the environment. In this study, a water jet was used to clean grease residues from steel wires for the first time. The EDS and SEM results of the steel wire rope surfaces and supplementary water jet impact experiments on galvanized steel plates revealed that when the pressure was lower than 50 MPa and the traverse speed was higher than 600 mm/min, the water jet caused minimal damage to the coating. When the pressure was 5 MPa, the cleaning ratio was between 45 and 60%, and the level of cleaning increased with increasing pressure. Two proposed concepts of exposure ratio and nonexposed area were applied to quantitatively analyze the theoretical upper and lower limits for grease that could be cleaned from two typical structures. The results showed that the lower and upper cleaning limits for structure 7 × 3 were 38.1% and 83.3%, while the lower and upper limits for structure 1 × 3 + 5 × 7 were 35.5% and 59.2%, respectively. This result explains why the grease content of structure 7 × 3 was lower than that of structure 1 × 3 + 5 × 7 after cleaning. In addition, the adhesion test results showed that adhesion to the two kinds of steel wire ropes after cleaning was increased by 126% and 145.71%, respectively, which means that additional processes for improving adhesion could be omitted after using a water jet for cleaning. This is an advantage that traditional cleaning processes do not offer.

Fabrication of Robust, Anti-reflective, Transparent Superhydrophobic Coatings with a Micropatterned Multilayer Structure.

Transparent superhydrophobic coatings with mechanical stability, self-cleaning function, and anti-reflective property have drawn much attention due to the great potential in a variety of real-world applications. In this work, we develop an ingenious approach to construct micropatterned transparent superhydrophobic coatings with a multilayer structure (water contact angle ∼153.6°, sliding angle ∼3.2°). A micropatterned ultraviolet-cured resist frame facilitates durability, while the modified silica nanoparticles, which are housed within the micro-cavities and bonded by an epoxy-based adhesive, impart superhydrophobicity. The micropatterned multilayer surface could endure sandpaper abrasion while maintaining satisfactory hydrophobicity. The prepared surfaces also retain the excellent water repellency after water jet impact, acid submerging, and mechanical bending, suggesting that they are sustainable in the case of adverse conditions and can be integrated with objects with non-flat geometries. Further, the superhydrophobic coatings exhibit an anti-reflection property while preserving high transparency. Taken together, we envision that the design strategies here can offer a practicable route to produce transparent superhydrophobic coatings for diverse outdoor applications.

Impact damage of composite laminates with high-speed waterjet

Rain erosion may cause substantial damage to aircrafts during supersonic flight. Such event is investigated here via high-speed waterjet impact on composite laminates. An experimental setup is developed to produce waterjets with the speed up to 700m/s and a finite element model of the waterjet-composite impact event is established. The consistency of experiment and simulation results validates the adopted numerical methods. The distribution of the water-hammer pressure is non-uniform and the maximum pressure occurs near the contact periphery when the water is about to eject laterally. After a high-speed (300∼560m/s) waterjet impacts a composite laminate, the impacted surface depression is observed, and the typical surface damage presents a central region with no visible surface damage surrounded by a faded “failure ring” with resin removal, matrix cracking and minor fiber fracture. Delamination occurs at the interfaces of adjacent layers with unequal dimensions and longitudinal matrix cracking appears on the back surface. Both the velocity and the diameter of waterjets are crucial factors on CFRP damage extents. Water-hammer pressure, the stagnation pressure and propagation of stress waves are failure mechanisms for most matrix damage in CFRP impacted by waterjets.

Low-cost preparation of durable, transparent, superhydrophobic coatings with excellent environmental stability and self-cleaning function

Transparent nanoparticle-based superhydrophobic coatings can be utilized in a variety of real-word applications. However, one major challenge that limits the practical applications in large-scale manufacturing is their poor durability or complicated fabrication procedures. Herein, we develop a simple and low-cost technique based on spin-coating to prepare double-layer structured superhydrophobic surfaces, where modified nanoparticles are attached to a semi-cured rough nanoparticle-epoxy layer. The average optical transmittance of the prepared coatings was 97.6% with pristine glass or PET as the substrates. The resultant water-repellent surfaces yield a static water contact angle of 153.4°±1.7° and sliding angle of 5.1°±1.1°. The nanocomposite surfaces also retain water repellency after tape-peeling, water jet impact, mechanical bending, heat treatment, HCl immersing, and UV irradiation, which makes the prepared surfaces sustainable in the case of outdoor situations. Further, the outstanding superhydrophobicity and durability of the coatings enable their excellent self-cleaning function. We envisage a combination of these attractive properties may provide a practical route for potential transparent applications.

Effect of Nozzle Outlet Type on the Flow Field Velocity and Impact Pressure of High-Pressure Water Jet Peening

Abstract Water jet peening can effectively improve the fatigue strength of metal materials, and the outlet shape of nozzle greatly affects the effect of water jet peening. In this paper, the effects of nozzle outlet shape on water jet velocity and impact pressure are studied by numerical simulation, and the jet velocity and dynamic pressure for different standoff distances are also discussed. The results show that the water jets of square, circular, and triangular nozzles are highly concentrated, and the water jet of elliptical nozzles is the most divergent. The axial velocity attenuation of the square nozzle along the axis is slower than that of the other three nozzles. The water axial velocity of the elliptical nozzle attenuates fastest, and the length of the core segment of the water jet is the smallest. Within a certain axial distance, the dynamic pressure area in the central area of the elliptical water jet is obviously larger than that of the other three nozzles, and the effective treatment range is large, which is more suitable for the welding surface strengthening operation.

Improved Smoothed Particle Hydrodynamics (SPH) Model for Simulation of Abrasive Water-Jet (AWJ)

Simulation of surface erosion by impact of abrasive water-jet (AWJ) is challenging for traditional mesh-based numerical methods, because it involves complex phenomena related to fluid–solid interaction, material removal and free surface flows. In this study, the surface erosion mechanism of ductile target materials by AWJ is investigated based on the smoothed particle hydrodynamics method (SPH, a mesh-free method). The water-jet, abrasives and solid target are all discretized with a series of SPH particles. The water-jet is modeled as a continuous fluid flow, the target material is modeled as a elastic–plastic material, and the abrasives are modeled as rigid bodies. The SPH model is improved by combining several correction algorithms and techniques, which help us to increase the stability and the accuracy of the simulation. The density diffusion correction term is introduced for water-jet, which reduces the pressure noise and makes the pressure field more stable. The dynamic boundary algorithm is used for the abrasives, and the pressure distribution around the abrasive is improved. The interactions among the water-jet, abrasives and solid target are realized by different contact algorithms. The dynamic process of plastic deformation, material removal and crater generation of the target material under AWJ impact can be simulated by the improved SPH model. The proposed model could be useful in the applications of AWJ machining and metal surface erosion.

Experimental investigation of the damage characteristics and breaking process of shale by abrasive waterjet impact

Perforation is critical to create a flow pathway between a shale reservoir and the production casing for hydraulic fracturing. However, the damage characteristics of shales by abrasive waterjet (AWJ) remain unclear. To address this concern, AWJ experiment is conducted for three types of shale with different mineral compositions, including siliceous shale, calcareous shale, and carbonaceous shale. X-ray diffractometry measures the content of mineral components. A rock mechanics test system obtains the main physical and mechanical parameters of shale samples. Scanning electron microscope (SEM) and acoustic emission (AE) are used to analyze the damage characteristics. The results indicate that siliceous shale with more brittle minerals is beneficial for the AWJ to create a larger perforation effectively, while carbonaceous shale with more clay minerals significantly lowers AWJ performance. For the shale with more brittle minerals, abrasive erosion and matrix spallation govern shale failures. As the clay content increases, the primary rock damage is abrasive cutting leading to the transgranular fracture. AE signals induced by AWJ impact could reflect breaking mechanisms and identify the difference in shale lithology. The energy dissipation gradually reduces during the AWJ process. Also, the dissipation has a negative linear correlation with the content of brittle minerals. This study provides fundamental insight into understanding shale damage by AWJ impact to optimize the perforation scheme.

Ice breaking by a high-speed water jet impact

Ice breaking has become one of the main problems faced by ships and other equipment operating in an ice-covered water region. New methods are always being pursued and studied to improve ice-breaking capabilities and efficiencies. Based on the strong damage capability, a high-speed water jet impact is proposed to be used to break an ice plate in contact with water. A series of experiments of water jet impacting ice were performed in a transparent water tank, where the water jets at tens of metres per second were generated by a home-made device and circular ice plates of various thicknesses and scales were produced in a cold room. The entire evolution of the water jet and ice was recorded by two high-speed cameras from the top and front views simultaneously. The focus was the responses of the ice plate, such as crack development and breakup, under the high-speed water jet loads, which involved compressible pressure ${P_1}$ and incompressible pressure ${P_2}$ . According to the main cause and crack development sequence, it was found that the damage of the ice could be roughly divided into five patterns. On this basis, the effects of water jet strength, ice thickness, ice plate size and boundary conditions were also investigated. Experiments validated the ice-breaking capability of the high-speed water jet, which could be a new auxiliary ice-breaking method in the future.

Hierarchical Artificial Compound Eyes with Wide Field-of-View and Antireflection Properties Prepared by Nanotip-Focused Electrohydrodynamic Jet Printing.

Artificial compound eyes (ACEs) endowed with durable superhydrophobicity, wide field-of-view (FOV), and antireflection properties are extremely appealing in advanced micro-optical systems. However, the simple and high-efficiency fabrication of ACEs with these functions is still a major challenge. Herein, inspired by moth eyes, ACEs with hierarchical macro/micro/nano structures were fabricated using the combination of nanotip-focused electrohydrodynamic jet (NFEJ) printing and air-assisted deformation processes. The NFEJ printing enables the direct and maskless fabrication of hierarchical micro/nanolens arrays (M/NLAs) without intermediate steps. The introduction of M/NLAs on the eye surface significantly improves the water hydrophobic performance with a water contact angle of 161.1° and contact angle hysteresis (CAH) of 4.2° and generally decreases the reflectance by 51% in the wavelength range of 350-1600 nm in comparison to the macroeye without any structures. The contact angle remains almost unchanged, and the CAH slightly increases from 4.2° to 8.7° after water jet impact for 20 min, indicating a durable superhydrophobicity. Moreover, the results confirm that the durable superhydrophobic ACEs with antireflection properties exhibit excellent imaging quality and a large FOV of up to 160° without distortion.

Numerical research on the dynamic rock-breaking process of impact drilling with multi-nozzle water jets

Based on the arbitrary Lagrangian-Eulerian finite element method (ALE-FEM), a coupling model for simulating the rock mass destruction process under the impact of a high-pressure water jet was established. Through the analysis of multi-nozzle jets’ impact on rock surface stress changes, the process of rock breaking and pore formation, and the rock breaking dynamic damage evolution, the mechanism of rock breaking by multi-nozzle jets was revealed by analyzing the stress distribution and dynamic damage of the rock mass during the impact process. The results show that nozzle jets with different inclination angles exhibit different rock breaking methods, which are mainly tensile failure and radial shear fracturing caused by the impact of the water jets. Rock breaking using multi-nozzle jets can be divided into four stages: the elastic deformation stage, the plastic deformation stage, the micro-fracture stage, and the complete failure stage. Based on the spatial-temporal evolution of the damage, the damage depth and scope of rock mass caused by multi-nozzle jets with different tilt angles are different. The results of this study provide a theoretical basis for the effect and optimization of the impact of multi-nozzle jets on rock breaking.

Modelling of water jet impact on molten metal

Splashes of high-temperature melt spreading over a water pool bottom can be a reason for the formation of a zone where melt, water and steam are mixed, providing conditions for powerful steam explosions. The paper considers the formation of melt splashes arising from the impact of a water jet on the surface of the melt. Numerical simulations are performed in 3D formulation, using the VOF method and an improved phase change model. The evolution of melt surface following the water jet impact is demonstrated, including the formation of a cavern, a primary melt splash known as the crown, as well as a secondary splash following the collapse of the cavern, known as the cumulative jet. Parametric study for the melt splash height dependence on the water jet geometry and velocity is carried out. The results of numerical analysis are discussed from the point of view of the similarity with respect to the momentum and kinetic energy of water jet. The significance of the results for the steam explosion problem is discussed.

Study on abrasive particle impact modeling and cutting mechanism

AbstractAbrasive water jet impact is widely applied in processing, oil fracturing, coal mining, rock crushing, and other engineering fields. The influence of abrasive particles on cutting performance is one of the main characteristics of this technology, which is different from pure fluid cutting. Therefore, as for improving the cutting performance of abrasive water jet, studying the cutting mechanism of abrasive water jet, and clarifying the mapping relationship between particle parameters and cutting, it is of great theoretical and practical significance to clarify the impact failure mechanism and material removal mechanism of abrasive particles in the process of high‐speed impact. In order to study the effect of abrasive particles on cutting performance, irregular abrasive particles are simplified to angular particles and circular particles in this paper. The impact shooting process of particles in abrasive jet cutting is numerically simulated by using smoothed particle hydrodynamics (SPH) method, and the target impact experiments are carried out. The fracture processes of ductile materials and brittle targets impacted by different shapes of particles are studied. The results are showed as follows. Firstly, the SPH numerical model has high accuracy and successfully reproduces the collision process of particles in the process of abrasive jet cutting, including the deformation mechanisms such as plowing, cracking and crushing of the target, and the error of the dent curve formed by the collision is less than 0.5 mm. Secondly, the impact mechanism of angular and circular particles is different for targets with different material properties. For ductile materials, the process of material accumulating to failure value is slow, mainly by the way of accumulation removal. And for brittle materials, it mainly produces plastic deformation and failure, without obvious material accumulation and extrusion area. Thirdly, different impact angles of particles have great influence on material removal.

Experimental investigation on the penetration characteristics of low-frequency impact of pulsed water jet

In this paper, experiments were conducted to investigate the penetration characteristics of low-frequency impact of pulsed water jet. The pulsed jet was generated with pulse length of 217 mm at the frequency of 120 Hz, using a round nozzle with diameter of 1 mm within the standoff distance of 40 mm. The macro characteristics (entrance shape, cross-section features, penetration depth, entrance area, and penetration rate), inner wall roughness, and micro morphology of penetration cavity on different targets (sandstone and granite) were measured to investigate the penetration performance and mechanism of low-frequency liquid impact. Results showed that there were two different penetration patterns on different targets based on the macro characteristics and the analysis of flow field loading characteristics in penetration cavity. The penetration cavities were present as funnel-shaped pits with narrow entrance and large depth on sandstone samples, and shallow craters with wide entrance and small depth on the granite samples. The roughness on entrance zone and bottom zone of penetration cavity on sandstone decreased with impact time and impact velocity, and that of middle zone increased. The roughness of cavity wall for granite increased with the expansion of penetration cavity. It was found that the main destruction pattern of sandstone was in the form of intergranular fracture, and transgranular fracture for granite. Radial confined holes were observed on the cavity wall at different depths, and the holes mainly existed along the grains boundary of sandstone, present on the transgranular fracture surface of granite. Based on the study about the macro failure characteristics, roughness, and micro morphology of penetration cavity, it was expected to provide some useful information for the application of penetration technology by low-frequency liquid jet.

AiStudy on the Behavior of an Underwater Explosion Bubble near a Rigid Wall

The dynamic approach to an underwater explosion (UNDEX) is a complex episode that involves shockwave propagation, bubble pulse with high pressure, and water jet impact. This paper proposes linkage of Finite Element Avenue (FEM) and Companion of Eulerian-Lagrangian (CEL) to supply promised data of large deformations and flow simulation of fluid and gas where the bubble interaction is near a stiff wall. To conduct the process, a 7.5 m x 9.0 m Eulerian domain and explosive charges of 10 g, 35 g, and 55 g TNT are built in a free field, respectively. Numerical analysis, as far as a comparison with research from E. Klaseboer, has been given in this study. The important results obtained from the CEL approach imply high expectations. In spite of the fact that this approach is not adequately consistent to totally supplant a live test, it can be utilized as an outline database to anticipate outcomes of managing an UNDEX with a high pressure bubble. The behavioral explosion from an UNDEX bubble near a rigid wall is a prospective contribution in this research. With these results, this technique can be used in further studies to examine UNDEX bubbles in the vicinity of deformable and complex structures.

Influence of Local Temperature Changes on the Material Microstructure in Abrasive Water Jet Machining (AWJM).

This article considers effects of local heat transfer taking place insteel cutting by abrasive water jet machining (AWJM). The influence of temperature changes during AWJM has not been investigated thoroughly. Most studies on AWJM suggest that thermal energy has little or no effect on the material cut. This study focused on the analysis of the material microstructure and indentation microhardness in the jet impact zone and the adjacent area. The structure features revealed through optical metallography and scanning microscopy suggest local temperature changes caused by the impact of the abrasive water jet against the workpiece surface. From the microscopic examinationand hardness tests, it is clear that, during the process, large amounts of energy were transferred locally. The mechanical stress produced by the water jet led to plastic deformation at and near the surface. This was accompanied by the generation and transfer of large amounts of heat resulting in a local rise in temperature to 450 °C or higher.

Damage and fracture characteristics of rocks with different structures under high-velocity water jet impact

This paper aims to investigate the damage and fracture characteristics of rocks with different structures under water jet impact. Three types rocks including heterogeneous coal, homogeneous sandstone, and transversely isotropic shale, were selected as the impact target rock. Water-jet impingement experiments with jet velocities varying from 447 m/s to 774 m/s were conducted. The rock macro-breakage characteristics were obtained by describing the breakage patterns, measuring the erosion depth and area, and counting the cracks number. A 3D reconstruction method based on the computed tomography and digital image processing technology was proposed to visualize the internal breakage characteristics and quantitatively analyze the damage field distribution. Combined with fracture morphology from scanning electron microscope, the failure mechanisms of rocks with three structures under water jet impact were revealed. The results indicate that coal, sandstone and shale will experience different breakage patterns with the increasing jet velocity: layered transverse cracks → “十”-type crack network → splitting crack, only one spindle-shape erosion pit, surface debris spalling → layered transverse cracks → “T”-type crack network. The effects of jet velocity and rock structure on the evaluation indexes (such as erosion depth and damage area, the number and angle of transverse cracks) were investigated thoroughly. In addition, the relationships between total damage degree based on breakage volume and jet velocity, and between damage variable based on breakage area and erosion depth, were compared and discussed. The failure mechanisms of three rocks impacted by water jets are as follows: (i) the reflection and interference of stress wave combined with the pressured water wedge effect cause the layered breakage and longitudinal splitting breakage of heterogeneous coal; (ii) the grinding effect of back flow mainly accounts for the formation of spindle-shape erosion pit in homogeneous sandstone; (iii) the shock stress wave effect and bedding structure lead to the spalling of large shale block and layered breakage, and the reflected wave tensile accompanied with pressured water wedge effect cause the tensile splitting breakage.