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Abstract

The major challenges facing engineers while fabricating high precision components from carbon fiber reinforced polymers (CFRP) especially when using an abrasive waterjet (AWJ) include the predominant interlaminar delamination and tapered kerfs. Therefore, in the present work, a comprehensive 3-D transient fluid-structure interaction (FSI) model is developed and numerically simulated to investigate mechanisms leading to delamination and hole-geometric defects while drilling autoclave cured aerospace grade multidirectional CFRP laminates. The FSI model comprised a two-way interaction between the computational fluid dynamics (CFD) flow model and structural finite element (FE) model. The CFD model explored the dynamic jet characteristics while impinging the anisotropic CFRP surface. The resulting forces from the CFD domain acted as loads in the transient FE model to predict the initiation of cracks and delamination. Subsequently, extensive experiments were conducted to validate the proposed numerical model. The results illustrated that during abrasive waterjet drilling of CFRP, delamination was initiated by the hydraulic impact as the abrasive waterjet penetrated the workpiece. Additionally, the study revealed that an increase in abrasive waterjet pressure and abrasive particle size resulted in a higher inter-ply debonding and crack propagation. Correspondingly, an increase in the standoff distance (SoD) resulted in reduced crack propagation and delamination. Further, the liquid-solid interface exhibited asymmetric cracks. The present findings not only provide requisite guidelines to achieving high-precision drilling of multidirectional CFRP but also provide technical guidelines to improving the performance characteristics of the abrasive waterjet machining (AWJM) process.

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... Based on the idea that utilizes solid particles erosion instead of eliminating it, one of the promising and innovative machining technologies called abrasive waterjet (AWJ) cutting is proposed by Hashish in early 1980s [1]. As the only cold highenergy beam processing technology in the world today, AWJ cutting has numerous benefits like no thermal distortion, high level of mobility, narrow kerf width, negligible heat effected zone, small cutting forces, etc. [2][3][4]. Almost all engineering materials can be cut by AWJ, especially the advanced difficult-to-cut materials such as ceramics [5]. Due to the specific characteristics of AWJ cutting, this processing technology has been used extensively in various industries in the past two decades. ...
... In this study, the target material is modeled as a rectangular block with the size of 400 * 400 * 200 3 . As mentioned above, the impacting area of the target material is modeled by SPH particles, and the rest is discretized by using the eight-node brick hexahedral elements with one integration point to reduce integration and hourglass control. ...
... According to the method proposed by Liu D et al. [29], the impact velocity of single abrasive particle can be estimated as = 0.75 ≈ 0.75 = 33.57√Ρ (3) where is the real impact velocity of single particle; is the theoretical impact velocity of single particle; ...
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In recent years, more and more researches have been carried out on the erosion mechanism of abrasive particles on target materials in the abrasive waterjet cutting process. However, the effect of material property factors on the target erosion damage is rarely studied systematically. In this work, a 3D smoothed particle hydrodynamics-finite elements model is established for the simulation. The controlled variable method is used to study how each material property factor affects the erosion process of single abrasive particle and to find out the key material property factors of Al6061-T6 and Ti-6Al-4V. The influence of the interaction of the key material property factors on the target erosion damage is further evaluated using the orthogonal test method.
... Based on the idea that utilizes solid particles erosion instead of eliminating it, one of the promising and innovative machining technologies called abrasive waterjet (AWJ) cutting is proposed by Hashish in early 1980s [1]. As the only cold high-energy beam processing technology in the world today, AWJ cutting has numerous benefits like no thermal distortion, high level of mobility, narrow kerf width, negligible heat effected zone, and small cutting forces [2][3][4]. Almost all engineering materials can be cut by AWJ, especially the advanced difficult-to-cut materials such as ceramics [5]. Due to the specific characteristics of AWJ cutting, this processing technology has been used extensively in various industries in the past two decades. ...
... The working pressure range of abrasive water jet cutting process is between 320MP a and 380MP a . And the incident velocity of abrasive particle is calculated according to formula (3). Finally, 630m/s is determined as the incident velocity of the impacting particle. ...
Article
Full-text available
In recent years, more and more researches have been carried out on the erosion mechanism of abrasive particles on target materials in the abrasive waterjet cutting process. However, the effect of material property factors on the target erosion damage is rarely studied systematically. In this work, a 3D smoothed particle hydrodynamics-finite elements model is established for the simulation. The controlled variable method is used to study how each material property factor affects the erosion process of single abrasive particle and to find out the key material property factors of Al6061-T6 and Ti-6Al-4V. The influence of the interaction of the key material property factors on the target erosion damage is further evaluated using the orthogonal test method.
... But their model is restricted to the prediction of damage initiation due to the primary jet impact on the anisotropic target. Based on the above results, Nyaboro et al. [80] established a comprehensive 3-D transient fluid-structure interaction (FSI) model to fill in the parts that were not involved in the former. Thongkaew et al. [81] utilized AWJ to conduct hole drilling and hole cutting for CFRPs, respectively, and compared the roundness errors and processing defects of those two methods. ...
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Owing to their excellent properties such as lightweight and high strength, fiber-reinforced composite materials are widely used as ideal materials for key structural components in extreme service environments (e.g., aviation, aerospace, and nuclear power). However, due to their non-uniformity and anisotropy, they have become typical difficult-to-machine materials, which are prone to cause damage during machining, thereby reducing the service life of the entire component. This review primarily summarizes the damage (including delamination, thermal damage, tool wear, and other processing damages) and suppression strategies of scholars in the process of traditional and non-traditional machining of fiber-reinforced composite materials in the past few years. Besides reviewing the research progress, the limitations of the current research were presented. From this review, it can be seen that traditional and non-traditional (e.g., laser machining) machining methods are difficult to avoid damage. Abrasive waterjet (AWJ) machining is a green and environmentally friendly machining technology. Some key issues are expected to be furtherly solved during the AWJ drilling of fiber-reinforced composite materials with low damage.
... Li et al. [16] compared the hole quality and its impact on tensile behaviour of plain woven CFRP laminates subjected to pure water jet (PWJ) and AWJ cuttings experimentally. Recently, the study of Nyaboro et al. [17] demonstrated that the delamination was triggered by an increase in abrasive waterjet pressure and abrasive particle size, but was lessened by the rise in the standoff distance. The impact angle of the jet is one of the critical parameters affecting the process quality. ...
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The abrasive water jet (AWJ) cutting technique is one of the promising techniques used in machining of composite materials due to lack of thermal damage, lower tool wear and higher productivity. In this study, the AWJ cutting of a cross-ply CFRP laminate was investigated experimentally and numerically. The purpose is to understand the underlying physics of the AWJ cutting of a composite plate, which can be later used to control the process as well as optimizing its parameters. In the performed tests of the plate with a stacking sequence of [0°/90°/0°/90°] and having a total thickness value of 0.84 mm, where the pressure of particles and impact angle were varied, different failure characteristics such as fiber pull-out, fiber breakage, fiber debonding, matrix cracking and delamination were noticed. A three-dimensional FE model of the process was developed using ABAQUS finite element software to understand the underlying physics. In the model, the pure water jet particles following the linear Hugoniot form of the Mie-Grüneisen equation of state and highly rigid abrasive particles were modelled using smooth particle hydrodynamics. While the three dimensional Hashin damage model was used to simulate the intra ply damage, cohesive zone elements were used to predict the delamination. The damage characteristics in the composite plate was investigated for different process parameters. When the speed of the AWJ particles increased from 300 m/s to 600 m/s, the amount of delamination decreased from 6.44% to 5.69% at the top interface with no more delamination observed at the middle and bottom interfaces. The delamination performance of 0°/90°/0°/90° orientation was found to be better than those of 0°/90°/90°/0° and 0°/0°/90°/90° orientations. The impact angle of the particles affected the material removal rate in the process significantly. The failure behaviour of the laminate subjected to AWJ and pure water jet cuttings (PWJ) were also compared.
... They described the delamination induced at the top surface by hydraulic shock. Nyaboro et al studied the AWJ drilling of CFRPs by using a two-way FSI model to investigate the delamination mechanism and hole geometry [123]. A high jet velocity or jet power increased the debonding area caused by delamination. ...
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This paper reports a comprehensive overview of nonconventional machining (NCM) of fiber-reinforced polymers (FRPs), which are widely used in high-tech industries owing to their superior mechanical properties compared with conventional metallic materials. To achieve FRP applications, hole processing for bolting and milling is required to match the dimensional precision. However, the large cutting force induced in conventional machining (CM), such as drilling and milling, causes severe failures, such as delamination and thermal damage to FRPs. To replace CM, various NCM technologies with efficient and powerful processing have been introduced to reduce FRP damage during machining. However, the complex nature of FRPs makes it difficult to identify the material removal mechanism and predict the machining quality and degradation of material properties. Not only the quantification of the machining parameter and performance but also an analysis to determine their relation is necessary. However, unlike many previous CM reviews, there are only a few reviews on NCM for FRPs. This paper addresses three types of representative NCMs: Laser beam machining, rotary ultrasonic machining, and abrasive water jet machining. Each NCM is classified and systematically reviewed using a parametric study, mechanistic model, and numerical simulation. In addition, further studies on the NCM of FRPs are suggested.
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Multi-Functionality of Polymer Composites: Challenges and New Solutions brings together contributions from experts in the field of multifunctionality, presenting state-of-the-art discussion of this exciting and rapidly developing field, thus key enabling technologies for future applications. The text will enable engineers and materials scientists to achieve multifunctionality in their own products using different types of polymer matrices and various nano- and micro-sized fillers and reinforcements, including, but not limited to, carbon nanotubes and graphene. In addition, technologies for the integration of active materials such as shape memory alloys are discussed. The latest developments in a wide range of applications, including automotive/aerospace, electronics, construction, medical engineering, and future trends are discussed, making this book an essential reference for any researcher or engineer hoping to stay ahead of the curve in this high-potential area.
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Carbon fiber reinforced plastics (CFRPs) are being used in various applications due to their light weight and good mechanical properties. However, the machinability of CFRPs is not good owing to machining induced damage. Moreover, the machining of micro features in CFRP products is a challenging task. The present research endeavour is an attempt to experimentally investigate a novel micro-size through hole electric discharge drilling (EDD) process for CFRPs. Through holes of diameter 110 µm were drilled using tungsten carbide electrodes (fabricated with wire electric discharge grinding). Experiments have been conducted by selecting input variables as voltage, capacitance and tool speed. A comparison of aspect ratio has been performed among the previous experimental studies and the current investigation. An aspect ratio of 10.9 (highest till date) has been achieved during drilling a micro hole of 110 µm diameter and 1.2 mm depth. Analysis of variance has been performed using Taguchi design of experiments and optimized set of parameters has been reported for maximum material removal rate and minimum tool were rate. The article also discuss the problems faced and their solutions, during drilling of micro through holes in carbon fiber reinforced polymer matrix composites.
Article
A computing technique for simulating the impact of a high-speed liquid jet on a wet wall is implemented. Such an impact generates shock waves in the jet, in the liquid layer on the wall, and in the gas surrounding the liquid. Also, the interphase boundary is strongly deformed by such an impact. The technique is based on the Constrained Interpolation Profile-Combined Unified Procedure (CIP-CUP) method combined with the dynamically adaptive Soroban grids. The gas-dynamic equations describing the liquid and gas flow are integrated without an explicit separation of the liquid-gas boundary. Such an approach is shown to be efficient for the considered problems. It allows us to obtain solutions without oscillations near the interfaces (including the case where they interact with the shock waves). For illustrative purposes, we provide the computational results for several one-dimensional and twodimensional problems with the typical features of the impact of a high-speed liquid jet on a wall, as well as a comparison with the known analytical and numerical solutions. The computational results for the problem of the impact of a high-speed liquid jet on a wall covered by a thin liquid layer are also presented.
Article
Abstract We propose a new approach named FEM-Stochastic approach for predicting the surface roughness resulting from waterjet peening of a metallic surface. This approach consists three aspects. One is Coupled Eulerian Lagrangian (CEL) simulation for studying the deformation behavior of single droplet; the second is the stochastic analysis for synthesizing a deformed surface; the third is to calculate the surface roughness parameters. CEL simulation results agree well with the liquid impact theory. Four situations with a different number of droplets (1000, 5000, 10,000 and 20,000) are analyzed, for which the deformed target surfaces and corresponding roughness profiles are shown and compared. Calculated values of roughness parameters indicate that there are three stages of evolution for the arithmetic average height Ra and quadrature average Rq. Those are: roughness increase stage, roughness decrease and roughness steady-state stage, respectively. The total roughness Rt and kurtosis parameter Rku decline gradually when more and more droplets are modeled because the sharp ridges formed by fewer droplets are obliterated by the impingement of subsequent droplets. Skewness parameter Rsk values are all negative, no matter how many droplets, moreover, its absolute value becomes increasingly smaller as the number of droplet changes from 1000 to 20,000. The present spatial model of droplets, although still incomplete, is capable of synthesizing a deformed surface and calculating the relevant roughness parameters.
Article
Ceramic sponge machining after firing is a great issue, requiring special tools and procedures because of the material peculiar macro-structure and its intrinsic brittleness. This study approaches the problem by exploiting the Abrasive Waterjet technology (AWJ) and showing its potential as a flexible tool. Nowadays, AWJ is coming up as an alternative to other ceramic manufacturing processes such as Grinding, Ultrasonic Machining and Laser Machining. The influence of a temporary pore filling agent, infiltrated in the already sintered sponge, is evaluated and its effect on the jet coherence is investigated through both modelling and experimental approaches. The most suitable process parameters are assessed in order to reduce the main AWJ defects in these conditions, setting the feed rate (vf) at 150 mm/min on a 35 mm thick 30 PPI (pores per inch) ceramic sponge on a conventional cutting equipment. The overall kerf divergence is therefore reduced down to less than 1° thanks to the filling procedure and then it is compensated by exploiting a 5-axis cutting centre. Defects are measured, using both conventional and ad hoc tools (e.g. CMM, grazing light surface inspection and digital image analysis). No thermal or chemical actions are applied by the AWJ cutting process and the negligible forces exerted on the struts preserve their integrity. A case study geometry is machined, fulfilling tight tolerances of 0.1 mm on a Ø 10 mm ceramic sponge cylinder over a 15 mm thickness. A complex-shaped component is cut on 35 mm thick sponge.
Article
Since experimental erosion testing is rarely feasible in the engineering practice, the estimate of erosion is often performed by numerical simulations. Computational Fluid Dynamics (CFD) codes are often equipped with utilities for wear estimation which rely on a well-established methodology. However, besides requiring stringent assumptions, this methodology involves a number of sub-models and parameterizations which, being difficult to define a priori, are potential sources of uncertainty. The objective of this work is to investigate how the erosion estimates are affected by the different sub-models and parameters of a CFD-based wear prediction model, so that its actual predictive capacity may be established. We referred to the benchmark case of the abrasive jet impingement test which, despite being widely studied both experimentally and numerically, highlights all the issues of impact erosion modelling. A systematic activity of simulation of previous experiments revealed the key role played by some fluid-dynamics related quantities, such as the formulation of the particle equation of motion, besides the erosion model. Moreover, it allowed providing guidelines for increasing the reliability of the estimates.
Article
Carbon fiber reinforced plastic (CFRP) composites have been intensively used in various industries due to their superior properties. In aircraft and aerospace industry, a large number of holes are required to be drilled into CFRP components at final stage for aircraft assembling. There are two major types of methods for hole making of CFRP composites in industry, twist drilling and its derived multi-points machining methods, and grinding and its related methods. The first type of methods are commonly used in hole making of CFRP composites. However, in recent years, rotary ultrasonic machining (RUM), a hybrid machining process combining ultrasonic machining and grinding, has also been successfully used in drilling of CFRP composites. It has been shown that RUM is superior to twist drilling in many aspects. However, there are no reported investigations on comparisons between RUM and grinding in drilling of CFRP. In this paper, these two drilling methods are compared in five aspects, including cutting force, torque, surface roughness, hole diameter, and material removal rate.
Article
Many delamination failure criteria based on fracture toughness have been suggested over the past few decades, but most only covered the region containing mode I and mode II components of loading because that is where toughness data existed. With new analysis tools, more 3D analyses are being conducted that capture a mode III component of loading. This has increased the need for a fracture criterion that incorporates mode III loading. The introduction of a pure mode III fracture toughness test has also produced data on which to base a full 3D fracture criterion. In this paper, a new framework for visualizing 3D fracture criteria is introduced. The common 2D power law fracture criterion was evaluated to produce unexpected predictions with the introduction of mode III and did not perform well in the critical high mode I region. Another 2D criterion that has been shown to model a wide range of materials well was used as the basis for a new 3D criterion. The new criterion is based on assumptions that the relationship between mode I and mode III toughness is similar to the relation between mode I and mode II and that a linear interpolation can be used between mode II and mode III. Until mixed-mode data exists with a mode III component of loading, 3D fracture criteria cannot be properly evaluated, but these assumptions seem reasonable.
Article
The usage of water jets has spread into numerous fields and for multifaceted purposes such as cleaning, cutting, and punching various materials. Because the impact occurs over an extremely short period, the target may deform elastically or plastically at high rates of strain. The dynamics of this process are complex and not fully understood. This paper applies a numerical method to simulate the phenomenon. A water jet with a spherical head was used at a speed of 570 m/s to impact on a structure, which was a flat plate made of Polymethyl-Methacrylate (PMMA). The Couple Eulerian Lagragian (CEL) method was used to simulate the entire process and eliminated abruption caused by large distortion of elements. Water-hammer pressure and the subsequent. stagnation pressure on the surface of the plate were performed to evaluate the distribution of the pressure on the impact surface and the resulting deformation of the structure. The simulation results were reflected in the calculation using empirical formulas and were further validated using Obara's experiment. Whereas facets of this phenomenon could not be fully modeled, the numerical simulation supplied accurate quantitative details of stress, strain, and deformation fields that would be costly and difficult to reproduce experimentally.
Article
A phenomenological model of the three-phase flow inside an abrasive water jet machining cutting head has been developed. Several improvements over previously presented models such as taking into account the abrasive particle size distribution, and the effect of breakage of particles on the energy flux have been made. The model has been validated using an extensive set of experimental data with wide variations in cutting-head geometry, operating pressure, and abrasive mass flow rates. The cross-sectional averaged abrasive particle velocity at the exit of the focussing tube has been predicted with good accuracy over the whole range of experiments. In particular, the Pearson correlation between the model and the experimental results is found to be more than 95%, implying the utility of this model in design.
Article
It is well-known that it is difficult to perform controlled-depth in abrasive waterjet (AWJ) milling, due to the dependency of the milled footprint not only on the jet kinematic parameters (e.g. jet traverse speed) but also on the jet energy parameters (e.g. pressure, abrasive mass flow, etc.). In this paper, an attempt has been made for modelling, simulation and validation of the AWJ footprint working in controlled depth (i.e. milling) mode at various jet traverse speeds and pump pressures at 90° incidence angles by using the finite element (FE) method. The proposed model is validated by comparing the material erosion rates and the profiles of the milled kerfs obtained by FE simulation to those generated from the experiments. The current model also simulates the effect of mass flow rate of the abrasive particles as well as the traverse rate of the AWJ plume across the workpiece.
Article
Abrasive water jet processes of glass are presented for crack-free machining of micro grooves and fluid polishing of micro channels with CFD analysis. In machining of the micro grooves, the abrasive is supplied to flow through intended machining area using the tapered masks. Stagnation under the jet and the horizontal flow on the machining area are controlled to generate crack-free surfaces by the mask shape. The same effect can be applied to polishing of the micro channels pre-machined by milling. Stagnation controlled by the inner wall of the channel changes the flow direction while keeping high fluid velocities.
Article
The impact of liquid drops upon polymers is important for several reasons. In particular, in cases of rain erosion after dro impact and of jets formed with cavities collapsing onto surfaces. An experimental study has detailed the evolution of damag within a material during loading. In particular, the temporal development of the pressure fields owing to the passage of stres waves leads to a series of failures in compression and tension from which erosion of the material and reduction in strengt results. This work follows from a previous paper in which a methodology was demonstrated by which liquid impact upon liqui masses was modelled. In this paper, the impact response of polymethylmethacrylate is reviewed and its response to impact evaluated. The comparison between jet and drop impact is examined in experiment and simulation. The numerical simulation is validate for jet impact and target response, and future uses of the technique in more complex interactions are suggested.
Article
The pressure in an impacting liquid drop against both a rigid and an elastic target is calculated for the period when the contact region is expanding faster than the wave speed in the liquid. For very low speed impact a geometrical-acoustics model is shown to give a good representation of the solution, until the edge speed approaches the wave speed. A self-similar solution, that takes account of nonlinear effects, is used in the neighbourhood of the contact edge. Comparisons are made with linear theory and numerical calculations. It is shown that linear theory is totally inadequate in predicting the escape of the shock system from the contact edge and that numerical calculations have used too large a time step to calculate the time of escape correctly. The delay in escape time from the previous theoretical predictions of Heymann (1969) is attributed to the elasticity of the target, an effect that is taken into account in the present work.
Article
SiC, Al2O3 and SiO2 particles in various grit sizes are characterized by image analysis in terms of their area, area diameter, width, length, width-tolength ratio W/L and perimeter squared-to-area ratio P2/A. Along with the mean, median and r.m.s. deviation of these parameters, the cumulative frequency distributions of the area and W/L are also obtained. W/L and P2/A are used as the indicators of particle shape. The particles become more elongated and less circular as the size of SiC and A12O3 particles increases and that of SiO2 particles decreases. The characterized particles are used for erosion studies on 18Ni(250) maraging steel in aged condition in a sand-blast type rest rig. The variation of erosion is studied with changes in size and shape of these particles. Erosion rate increases with increasing particle size for SiC and Al2O3 particles up to a certain value and decreases for SiO2 particles. However, it increases with increasing P2/A and decreasing W/L for all three types of particles. Erosion behavior is analyzed considering the effect of rake angle in ploughing and microcutting as observed in erosion. It is the changing contribution from ploughing and cutting with changes in shape and size of particles that accounts for erosion variation.
Article
An abrasive water‐jet cutting process is a process in which water is pressurized up to a very high value and forced through a very small orifice to form a very thin high speed jet beam. This thin jet beam is then directed through a chamber and fed to a secondary nozzle, which is called mixing tube. During this process, a vacuum is generated in the chamber, and abrasives and air are pulled into the chamber, through an abrasive feed tube. Usually, it takes a short time for abrasives to travel through the length of the tube and to be entrained into the jet. Before that, the jet impinging onto the solid surface is void of abrasives. During that short moment, the target material is exposed to a very high dynamic load. Although this high dynamic load only acts on target material for a very short period of time, its high value may crack target material quickly. This paper explores the theory behind the cracking phenomenon. Based on this exploration, understanding the piercing process completely becomes feasible.
Article
This paper describes a theoretical investigation into (i) the response of a spherical particle to a one-dimensional fluid flow, (ii) the motion of a spherical particle in a uniform two-dimensional fluid flow about a circular cylinder and (iii) the motion of a particle about a lifting aerofoil section. In all three cases the drag of the particle is allowed to vary with (instantaneous) Reynolds number by using an analytical approximation to the standard experimental drag-Reynolds-number relationship for spherical particles.
Article
The impact properties of composites of glass fibre or carbon fibre in polyester or epoxy resin were studied. Impact was by high-velocity water jets ( approximately 700 ms-1), which previous work has shown successfully simulate rain erosion damage and other impact situations involving high-stress (of the order of 1 GPa) and short-duration (few mu s) loading. The failure of the composites is analysed and the damage mechanisms are identified. An assessment is made of the effect of such variables as reinforcement geometry, volume fraction of fibres, matrix toughness, void content and surface condition.
Article
The paper reports on the deformation and fracture of four rock materials and two cementitious materials due to the impingement of simulated liquid drops at velocities up to 900 m/s. For hard materials, the damage appeared in the form of an undamaged central region surrounded by rings of discrete microcracks. The size of the undamaged zone corresponded to the theoretical contact diameter for low and medium impact velocities, whereas the outer ring size corresponded to the simulated drop diameter. For soft materials, crack formation was obliterated by features of plastic flow. An elastic–plastic transition criterion was derived to explain these different types of response. Crack ring diameter increased as impact velocity increased. However, for rather non-homogeneous materials this relationship was very weak. Failure due to lateral jetting could be noted and was found to contribute significantly to the damage. Material was removed by two different modes: drilling mode and chipping mode, respectively. The first mode applied to soft and porous materials, namely limestone and sandstone, whereas the second mode applied to rather dense and brittle materials, namely granite and feldspar.
Article
In dealing with fluid impact and large deformation problems by traditional Lagrange grid, calculation failure often happens due to grid distortion. An abrasive water jet machining model is created to simulate the whole stage by software LS-DYNA from the jet into the nozzle to the workpiece material removal process using ALE (Arbitrary Lagrange–Euler) algorithm. The mesh for the abrasive and water is based on the ALE formulation, while the target mesh applies the Lagrange formulation. The effect of jet penetration is implemented by coupling the grids of ALE and Lagrange. The jet traverse speed is achieved by definition of the movement of ALE grid to reduce the mesh domain. The abrasive constitutive equations are also presented in this paper. The uniform mixture for abrasive and water is achieved by definition of volume percentage of the two materials in the initial ALE elements. Simulation results give the relationships between processing parameters and the cutting depth. The good agreement between simulation results and experimental data verifies the correctness of the simulation. KeywordsAbrasive water jet–Abrasive constitutive model–ALE–Fluid–solid coupling
Article
Delamination is a major component defect when machining composites or layered materials. This study aims to explore the mechanism of delamination in graphite/epoxy composites under abrasive waterjet (AWJ) machining. It is found that crack tips are generated by the shock wave impact of the waterjet at the initial cutting stage, while delamination is a result of water penetration into the crack tips that promotes water-wedging and abrasive embedment. Based on an energy conservation approach, a semi-analytical model is developed to predict the maximum delamination length generated by an AWJ. The model prediction is found in good agreement with the experimental data and can be used as a practical guide for process planning to minimise or eliminate the delamination defects on the components in AWJ machining of graphite/epoxy composites.
Article
Layered composites are “difficult-to-machine” materials as it is inhomogeneous due to the matrix properties, fibre orientation, and relative volume fraction of matrix. Abrasive waterjet cutting has proven to be a viable technique to machine such materials compared to conventional machining. This paper presents an investigation on the kerf taper angle, an important cutting performance measure, generated by abrasive waterjet (AWJ) technique to machine two types of composites: epoxy pre-impregnated graphite woven fabric and glass epoxy. Comprehensive factorial design of experiments was carried out in varying the traverse speed, abrasive flow rate, standoff distance and water pressure. Using the dimensional technique and adopting the energy conservation approach, the kerf taper angle has been related to the operating parameters in a form of a predictive model. Verification of the model for using it as a practical guideline has been found to agree with the experiments.
Article
The paper investigates the potential of cohesive interface elements for damage prediction in laminates subjected to low-velocity impact. FE models with interface elements adopting a bilinear cohesive law were first calibrated and validated by simulation of standard fracture toughness tests and then employed to model the impact response of cross-ply graphite/epoxy laminated plates.The developed model provided a correct simulation of the impact response of laminates in a wide range of energy values and successfully predicted size, shape and location of main damage mechanisms. The results of the analyses also pointed out the importance of employing a damage criterion capable of accounting for the constraining effect of out-of-plane compression on the initiation of the decohesion phase.
Article
A new approach is presented for the analysis of transient waves propagating in composite laminates. The wavelet transform (WT) using the Gabor wavelet is applied to the time–frequency analysis of dispersive plate waves. It is shown that the peaks of the magnitude of WT in the time–frequency domain are related to the arrival times of group velocity. Experiments are performed using a lead break as the simulated acoustic emission source on the surface of quasi-isotropic and unidirectional graphite/epoxy laminates. For predictions of the dispersion of the flexural mode, Mindlin plate theory is shown to give good agreement with the experimental results. The planar source location based on the flexural wave is performed using a triangulation method. The use of frequency-dependent arrival time of output signal and angular dependence of group velocity provides accurate results of source location for anisotropic laminates.
Article
Delamination is a major concern in the manufacturing processes of composite materials. It reduces not only the structural integrity of the laminate but also the long-term reliability of the assembly. Water jet drilling, in spite of its advantages of no tool wear and thermal damage, often creates delamination composite laminate at bottom. The current paper presents an analytical approach to study the delamination during drilling by water jet piercing. The analysis uses fracture mechanics with plate theory to describe the mechanism of delamination. This model predicts an optimal water jet pressure for no delamination as a function of hole depth and material parameters (opening-mode delamination fracture toughness and modulus of elasticity). Good agreement is achieved with data obtained from water jet drilling of graphite epoxy laminate. The predicted optimal water jet pressure can be applied in a control scheme for maximizing the productivity of water jet drilling of composite laminates.
Article
The paper describes a high resolution method (CICSAM) for the accurate capturing of fluid interfaces on meshes of arbitrary topology. It is based on the finite-volume technique and is fully conservative. The motion of the interface is tracked by the solution of a scalar transport equation for a phase-indicator field that is discontinuous at the interface and uniform elsewhere; no explicit interface reconstruction, which is perceived to be difficult to implement on unstructured meshes, is needed. The novelty of the method lies in the adaptive combination of high resolution discretisation schemes which ensure the preservation of the sharpness and shape of the interface while retaining boundedness of the field. The special implicit implementation presented herein makes it applicable to unstructured meshes and an extension to such grids is presented. The method is capable of handling interface rupture and coalescence. The paper outlines the methodology of CICSAM and its validation against academic test cases used to verify its accuracy.
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