Numerical simulation of solid particle impacts on Al6061-T6 Part II: Materials removal mechanisms for impact of multiple angular particles

In the accompanying paper (M. Takaffoli, M. Papini, Numerical simulation of solid particle impacts on Al6061-T6 Part I: Three dimensional representation of angular particles), it was demonstrated that realistic 3D models of angular particles could be generated and used with a smoothed particle hydrodynamics model to simulate the damage done to an Al6061-T6 target due to many non-overlapping particle impacts. In this paper, the same methodology was used to simulate overlapping impacts, and thus the material removal mechanisms associated with the solid particle erosion of this material. The evolution of the topography of the blasted surface was simulated, and the surface ripple patterns that typically form during the erosion of aluminum alloys were observed. The predicted volumetric erosion rates at different impact angles were, on average, within 7% of those measured in erosion experiments. An investigation of the simulated trajectory of the impacting particles revealed the cooperative contribution of overlapping impacts to material loss, and solid particle erosion mechanisms such as the micromachining of chips, the ploughing of craters, and the formation, forging and knocking off of crater lips. The results indicate that numerical simulation of the solid particle erosion of ductile metals by realistic angular particles is possible.     

Experimental verification of a model of erosion due to the impact of rigid single angular particles on fully plastic targets

A previously described rigid-plastic model of the erosion of ductile targets by the impact of single angular particles was experimentally verified over a wide range of particle angularities, incident angles of attack, and incident orientation angles. The model assumes that the particle is perfectly rigid and thus is non-deforming, while the target material response is fully plastic, so that elastic rebound effects are neglected.Measurements of particle rebound kinematics, crater volume, and crater shape revealed generally good agreement with those predicted by the rigid-plastic model, and erosion mechanisms resulting from particles tumbling either forwards or backwards, were identified. For highly angular particles, target material removal sometimes occurred due to tunnelling of the particles below the target surface, leading to early break-off of a machined chip, behaviour that could not be predicted by the rigid-plastic model. Besides providing insights into fundamental erosion mechanisms, the results of the present study can be used to predict particle rebound kinematics, crucial for simulations of erosive streams which take into account interference between incident and rebounding particles.     

Solid particle erosion studies using single angular particles

Studies have been made of the oblique impact of individual angular particles on lead and mild steel targets, and the influence of the particle orientation at the point of impact on the subsequent deformation determined. When the angle made by the leading edge of the particle to the surface is small, ploughing deformation can occur, similar to that found with spherical particles. At a sufficiently high impact velocity, material is removed from the surface. If the angle between the surface and the leading edge of the particle is larger, a micromachining action occurs. However, rather than scooping out material as a chip, the cutting edge of the particle tends to bury itself deeply into the specimen. Material can be removed as a result of a particle breaking up during its cutting action. Here, a lip raised during the early stages of the impact is subsequently cut off by fragments of the particle. It is shown that particle rotation can take place during impact and that when this happens the particle's effectiveness in removing material is diminished. Bands of intense deformation are visible in etched sections of craters in mild steel formed in some experiments. It is suggested that these are adiabatic shear bands.     

Investigating the optimum molybdenum disulfide (MoS2) nanolubrication parameters in CNC milling of AL6061-T6 alloy

Aluminum 6061-T6 is an important alloy as it has dominant mechanical properties like weldability and hardness, and has the potential to be used at variable temperatures. AL6061-T6 is frequently used in the aerospace industry, as well as aircraft, automotive, and packaging food industries. Milling of Al6061-T6 is important especially to produce various product shapes for adapting to diverse applications. The aptitude of the CNC milling machine for batch production would be a noteworthy advantage. However, the demand for high quality brings attention to product quality, particularly the roughness of the machined surface because of its effect on product appearance, function, and reliability. Introducing correct lubrication to the machining zone could improve the tribological characteristics of Al6061-T6. For additional improvement, applying nanolubrication may produce superior product quality, as the rolling action of billions of nanoparticle units in the tool chip interface can significantly decrease the cutting forces. In this research work, the optimum MoS₂ nanolubrication parameters in Al6061-T6 milling to achieve the lowest cutting force, cutting temperature and surface roughness are investigated. The parameters include nanolubricant concentration, nozzle orientation and air carrier pressure. Taguchi optimization along with standard orthogonal array L₁₆(4³) are employed. Furthermore, surface roughness and cutting force are analyzed via signal-to-noise (S/N) response analysis and the analysis of variance (Pareto ANOVA) in the hopes of achieving optimum conditions and to determine which process parameters are statistically significant. Finally, optimization improvements are investigated through confirmation tests.     

Numerical Study of Impact Behaviors of Angular Particles on Metallic Surface Using Smoothed Particle Hydrodynamics

Modeling and studying the impact behaviors of angular particles is critical in understanding the mechanisms of erosive wear on solid surfaces. This article focuses on effective mesh-free model based on the smoothed particle hydrodynamics (SPH) method to simulate impacts of angular particles on metallic surfaces. The predicted results are compared with the available experimental data, and good agreement has been achieved. Our simulations under different incident conditions successfully reproduce the general impact behaviors of angular particles, including rotating behavior and rebound behavior, which enables detailed examinations of erosion mechanisms. We find that the rotating behaviors are mainly determined by initial orientation and impact angle, whereas impact velocity has little effect. For backward impact involving a prying-off action, there generally exsits a critical impact velocity below which the cutting process would never be finished, which may result in a rebound angle greater than 90°. Further, multiple and overlapping impacts are simulated to reveal the effect of a pre-created crater on the subsequent impact. The results demonstrate the ability of the present model to handle the extremely deformed surface by overlapping impacts. The proposed SPH model and the present study could be useful in the study of erosive wear on the surface of metal devices that carry granular substances.     

6061-T651铝合金动态力学性能及J-C本构模型的修正

为合理描述6061-T651铝合金的应力流动行为,利用万能材料试验机和霍普金森压杆,分别进行准静态、高温和高应变率下的材料力学性能测试,获得材料在不同条件下的应力应变曲线。基于试验结果,修正Johnson-Cook本构模型得到MJC(Modified Johnson-Cook)模型,并标定MJC模型各项参数。为校验MJC模型及参数的有效性,利用一级气炮发射直径为5.95 mm的圆柱弹体冲击刚性靶的Taylor杆试验以及直径为12.68 mm的刚性弹撞击厚度为2 mm靶板的试验。最后,采用ABAQUS/Explicit有限元软件建立Taylor杆和弹靶冲击试验的三维模型,基于MJC本构模型进行Taylor杆冲击、以及结合MMC(Modified Mohr-Coulomb)断裂准则进行弹靶冲击的数值模拟计算。研究结果表明,修正的MJC本构模型能够有效地描述6061-T651铝合金材料在大应变、高应变率和高温下材料的应力流动行为和变形行为。     

Investigation of subsurface damage considering the abrasive particle rotation in brittle material grinding

This paper presents the feasibility study of potential application of recently developed surface defect machining (SDM) method in the fabrication of silicon and similar hard and brittle materials using smooth particle hydrodynamics (SPH) simulation approach. Simulation study of inverse parametric analysis was carried out to determine the Drucker-Prager (DP) constitutive model parameters of silicon by analysing the deformed material response behaviour using various DP model parameters. Indentation test simulations were carried out to perform inverse parametric study. SPH approach was exploited to machine silicon using conventional and surface defect machining method. To this end, we delve into opportunities of exploiting SDM through optimised machining quality, reduced machining time and lowering cost. The results of the conventional simulation were compared with the results of experimental diamond turning of silicon. In the SPH simulations, various types of surface defects were introduced on the workpiece prior to machining. Surface defects were equally distributed on the top face of the workpiece. The simulation study encompasses the investigation of chip formation, resultant machining forces, stresses and hydrostatic pressure with and without SDM. The study reveals the SDM process is an effective technique to manufacture hard and brittle materials as well as facilitate increased tool life. The study also divulges the importance of SPH evading the mesh distortion problem and offer natural chip formation during machining of hard and brittle materials.     

Investigation on surface finish and metallic particle emission during machining of aluminum alloys using response surface methodology and desirability functions

The surface finish of a mechanical part plays an important role as it determines the part’s field performance. The machining parameters and conditions governing the part surface finish also impact on the other machining process performance indicators such as tool wear, tool life, cycle time, machining cost, and undesirable emissions of aerosols and metallic particles. In today’s metal cutting industry, a major concern is the occupational safety and health hazard associated with cutting fluids usage and metallic particle emission. It is therefore necessary to determine machining conditions that could improve the part surface finish while maintaining low the aerosol emission. In this research study, statistical methods are used to study the surface finish parameters and the metallic particle emissions during milling of aluminum alloys (6061-T6, 7075-T6, and 2024-T351) with two coated carbide tools (TiCN and a multilayer TiCN?+?Al₂O₃?+?TiN). Following an implementation of multilevel design of experiment, machining trials and determination of mains most influential factors, surface responses and desirability functions are used to determine the best process operational conditions and windows. The results of this research demonstrate that TiCN-coated tool generates fewer respirable airborne particles during machining than multilayers TiCN?+?Al₂O₃?+?TiN-coated tool. Overall, it is shown that the use of TiCN coating tool provides a better opportunity for an environmentally benign dry machining along with improvement on surface quality.     

An investigation of optimum SiO2 nanolubrication parameters in end milling of aerospace Al6061-T6 alloy

Aluminium AL6061-T6 is a common alloy which is used for many purposes since it has the superior mechanical properties such as hardness and weldability. It is commonly used in aircraft, automotive and packaging food industries. Milling of Al6061-T6 would be a good process especially in producing varieties shape of products to adapt with different applications. The capability of the CNC milling machine to make batch production would be a noteworthy advantage. However, the demand for high quality focuses attention on product quality, especially the roughness of the machined surface, because of its effect on product appearance, function and reliability. Introducing correct lubrication in the machining zone could improve the tribological characteristic of Al6061-T6 leading to higher product quality. In this research work, the optimum SiO₂ nanolubrication parameters in milling of Al6061-T6 are investigated to achieve correct lubrication conditions for the lowest cutting force, cutting temperature and surface roughness. These parameters include nanolubricant concentration, nozzle angle and air carrier pressure. Taguchi optimization method is used with standard orthogonal array L₁₆(4)³. Furthermore, analyses on surface roughness and cutting force are conducted using signal-to-noise (S/N) response analysis and the analysis of variance (Pareto ANOVA) to determine which process parameters are statistically significant. Finally, confirmation tests were carried out to investigate the optimization improvements.     

Thermo-mechanical finite element model of friction stir welding of dissimilar alloys

A thermo-mechanical finite element model is developed based on Coupled Eulerian Lagrangian method to simulate the friction stir welding of dissimilar Al6061-T6 and Al5083-O aluminum alloys using different tool pin profiles. The model is validated using published measured temperatures and weld microstructure. The finite element results show that maximum temperatures at the weld joint were below the materials’ melting point. Placing the harder alloy (Al6061-T6) at advancing side led to a decrease in maximum process temperature and strain rate, but increased tool reaction loads. Featured tool pin produced better material mixing resulting in enhanced joint quality with reduced volumetric defects.     

Fluid dynamic mechanisms of particle flow causing ductile and brittle erosion

Traditional prediction of erosion focuses on the use of velocity and impact angle of particles as independent variables in analytically derived models. This approach is most suitable for numerical predictions of erosion in disperse flow fields where particle trajectories may easily be followed prior to impact. For dense particle flows, the prediction of individual particle or particle cluster movement is nearly never attempted by following trajectories. Instead, two-fluid Eulerian–Eulerian approaches are used in which a continuous particle fluid phase is considered.The present study shows that the impact velocity and angle of attack of particles at the eroding surface are difficult to obtain for dense flows, thus being difficult to consider as parameters for predicting erosion. Instead, it is proposed that the normal and the shearing components of the viscous dissipation of the particulate phase are more suitable as independent flow variables governing the erosion process. These variables describe deformation and cutting wear processes, respectively, and are readily derived from the flow field.Eulerian erosion models are proposed, based on these independent variables. It is possible to implement previous results and theories concerning the material–mechanical interaction between the abrasive and an eroding surface to achieve model improvements. In this work, only a simple model taking into account a threshold elastic strain limit is proposed, to more correctly model the deformation wear.The particle-flow boundary condition — a partial-slip condition — significantly influences the erosion process, particularly the cutting erosion. The boundary condition depends on parameters such as the local particle phase flow, the mean diameter and the sharpness of the abrasive as well as the surface roughness.A simple 2D test application — a jet stream of particles impinging a tilted plate — is presented, and the qualitative angular behaviour of ductile and brittle erosion is reproduced at the target position. A scheme is presented for determination of material constants and suitable boundary conditions to be used in the proposed erosion models.     

Advancement and characterization of Al-Mg-Si alloy using reinforcing materials of Fe2O3 and B4C composite produced by stir casting method

The modifications of Al6061-T6 metal matrix composites is an extraordinary enthusiasm of recent pertinence for lesser weight materials with high value of tensile strength, hardness and wear protection, which can be widely used in automotive and aircraft design. In this paper, we investigate the impacts of the reinforced Al6061 composite with 5 wt% of Fe₂O₃ in addition to 2 %, 4 %, 6 % weight of B₄C being made-up by stir casting technique. In this research, Al6061 composites have analyzed by its physical and mechanical properties like as density, hardness, impact strength, ultimate tensile and compressive strength, and an optical microscope is utilized to assess the metallurgical properties such as microstructure with different wt% of reinforcement of Al6061 composite. The microstructure of newly prepared composites was shown a regular spreading of reinforcements in the matrix by an optical microscope and also the muscular bonding between the matrix and reinforcements were demonstrated by SEM analysis. It is further identifying that, microstructure uniformity and therefore the tensile strength of the metal composites was enhanced with increasing the fraction of Fe₂O₃ and B₄C particles without any decrement in elongation.

     

面向流屑角突变建模的切削状态参数经验公式的获得及应用

从提高流屑角突变模型的预测精度出发,建立了切削状态参数与3个切削控制参数之间关系的新经验公式。提出了一种通过迭代法准确设定有限元仿真软件刀-屑摩擦因数的方法,并通过直角切削Al6061-T6工件的有限元仿真试验,获得了一组不同切削控制参数组合条件下的切削状态参数数据。根据该数据拟合出剪切角φ、刀-屑摩擦角β、剪切应力τs关于刀具前角γ0、进给量f和切削速度v的经验公式,并通过一组直角切削试验,验证了所得经验公式的有效性。将新建经验公式应用于流屑角突变建模过程后,所得模型关于突变临界切削宽度的平均预测误差减小了27.2%。     

Abrasive Waterjet Machining Simulation by Coupling Smoothed Particle Hydrodynamics / Finite Element Method

In dealing with abrasive waterjet machining(AWJM) simulation,most literatures apply finite element method(FEM) to build pure waterjet models or single abrasive particle erosion models.To overcome the mesh distortion caused by large deformation using FEM and to consider the effects of both water and abrasive,the smoothed particle hydrodynamics(SPH) coupled FEM modeling for AWJM simulation is presented,in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FEM.The two parts interact through contact algorithm.Utilizing this model,abrasive waterjet with high velocity penetrating the target materials is simulated and the mechanism of erosion is depicted.The relationships between the depth of penetration and jet parameters,including water pressure and traverse speed,etc,are analyzed based on the simulation.The simulation results agree well with the existed experimental data.The mixing multi-materials SPH particles,which contain abrasive and water,are adopted by means of the randomized algorithm and material model for the abrasive is presented.The study will not only provide a new powerful tool for the simulation of abrasive waterjet machining,but also be beneficial to understand its cutting mechanism and optimize the operating parameters.     

6061-T6铝合金薄板剪切试件设计及动态剪切力学特性分析

车身结构影响了整车的碰撞安全性,其中车身承载部件在碰撞过程中主要表现为剪切失效,因此需要对车身材料的动态剪切力学特性展开研究。为了描述6061-T6铝合金材料在复杂工况下的力学特性,进行了准静态和动态力学性能试验。基于不同应力状态和应变率下铝合金力学性能的测试数据,标定了材料的本构模型和断裂模型参数,并通过对比试验与仿真结果验证了材料参数的准确性。为了实现拉伸试验机开展铝合金薄板剪切试验,设计四种形状的薄板剪切试件,采用数值模拟对比所设计剪切试件的应力及应变分布,并分析不同剪切应变率对6061-T6铝合金材料剪切力学特性的影响规律。结果表明：圆形开口对称试件适用于研究塑性变形阶段的失效断裂,而圆形开口偏置试件适用于研究弹性变形阶段的应力应变关系。在低剪切应变率范围内,6061-T6铝合金无显著的应变率强化效应,然而随着应变率的增加敏感性有所提高。     

SPH method applied to high speed cutting modelling

The purpose of this study is to introduce a new approach of high speed cutting numerical modelling. A Lagrangian smoothed particle hydrodynamics (SPH)-based model is carried out using the Ls-Dyna software. SPH is a meshless method, thus large material distortions that occur in the cutting problem are easily managed and SPH contact control permits a “natural” workpiece/chip separation. The developed approach is compared to machining dedicated code results and experimental data. The SPH cutting model has proved is ability to account for continuous to shear localized chip formation and also correctly estimates the cutting forces, as illustrated in some orthogonal cutting examples. Thus, comparable results to machining dedicated codes are obtained without introducing any adjusting numerical parameters (friction coefficient, fracture control parameter).     

Numerical simulation of single particle acceleration process by SPH coupled FEM for abrasive waterjet cutting

The existing numerical simulations of hydrodynamic characteristics of abrasive waterjet in a cutting head were mainly based on Eulerian grid or arbitrary Lagrange–Eulerian grid method to establish computational fluid dynamics models. However, using these two methods, the abrasive and water were premixed and given an identical initial velocity, which were different from the mixing and acceleration processes of abrasive in the cutting head. This paper presents a more suitable numerical model that the abrasive particle enters into the mixing chamber in a low velocity and is accelerated in the focus tube by a high-speed waterjet from the orifice. In order to model this mixing-and-acceleration process of abrasive and high-speed waterjet, the smooth particle hydrodynamics (SPH) coupled finite element method (FEM) is adopted, in which SPH particles are used to model the high-speed waterjet to adapt its extremely large deformation and FEM is applied to model the discrete abrasive particle, cutting head, and workpiece. As a result, evolution of abrasive and waterjet velocities along focus tube is analyzed; trajectory of single abrasive particle in focus tube is sighted; the relationships between abrasive particle velocities and different water pressures are described; the rule of outlet velocities of abrasive particle vs. dimensionless ratio of diameter is conducted; depth of penetration caused by single abrasive particle impact is obtained. The current model is validated by the existing theoretical and experimental data.     

Solid particle erosion behaviour of Ti6Al4V alloy

Abstract

The effects of particle impingement angle, impingement velocity and erodent particle size on the erosion rate and surface morphology of the Ti6Al4V alloy have been investigated comprehensively in order to evaluate solid particle erosion behaviour of Ti6Al4V alloy. Samples were eroded in a specially designed sandblasting system under various parameters using alumina (Al₂O₃) erodent particles. Surface morphology investigations were examined by scanning electron microscope using various analysis and modes (energy dispersive X-ray analysis, elemental mapping and compositional contrast). Ti6Al4V alloy showed ductile behaviour with a maximum erosion rate at 30° impingement angle. Erosion rate of Ti6Al4V alloy increased with increases in velocity and decreased with increases in erodent particle size. Scanning electron microscopy investigations of eroded surfaces of Ti6Al4V alloy samples reveal the dominant erosion mechanism such as microploughing, microcutting and plastic deformation. Embedded erodent particles on the surfaces of Ti6Al4V alloy nearly at all particle impingement angles and velocities were clearly detected.     

Research on chip formation parameters of aluminum alloy 6061-T6 based on high-speed orthogonal cutting model

Chip formation, an important aspect of the high-speed cutting (HSC) mechanism, is generally accepted as the result of shear deformation in the shear zone and tool-chip friction. In order to accurately study chip formation process in HSC, a theoretical model for the high-speed orthogonal cutting of aluminum alloy 6061-T6 was built, which can be used to calculate the important parameters of chip formation, such as shear angle, friction angle, length of shear plane, tool-chip contact length, and width of the first shear zone. A series of orthogonal cutting experiments, with the YG6 carbide tool and on a wide range of cutting speed (100–1,900 m/min) and feed (0.06–0.15 mm/r), were performed in order to obtain the parameters required in the model, including the cutting forces, the chip thickness, and the shear slip distance. Seven kinds of chip formation parameters were obtained with different cutting parameters in the experiment, and the built theoretical model can well explain the formation process and the morphology characteristics of these chips, which proves that the combined method of theoretical model and orthogonal cutting experiment is an effective and easy approach to obtain the parameters of chip formation in HSC, avoiding the cutting speed limitation and the safety risk in quick-stop test. Within the range of parameters set in the experiments, the chip mainly appears to be continuous chip, curling chip, or discontinuous chip. And the chip thickness, friction angle, length of shear plane, and width of the first shear zone decrease with the increase of the cutting speed; meanwhile, the shear slide distance and shear angle increase.     

Erratum to “The effect of particle size on the erosion of a ductile material at the low particle size limit” [Wear 233–235 (1999) 727–736]

The intrinsic particle size dependence of erosion rate was investigated in the absence of aerodynamic effects. An apparatus was designed to impact small particles on metallic substrates at normal incidence in vacuum. Two types of target materials, Cu–30% Zn and pure Ti, were impacted with SiO₂ particles with average diameters of 2, 5 and 25 μm. The velocity of impact was 12 m/s. Damage processes induced by single particles were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). This latter technique allowed for the measurement of impact profiles, both of the cut surfaces and the associated displaced material pile-ups. The impacts produced were, in many cases, asymmetrical, and the asymmetries appeared to be related to the orientation of the impacted surface. The appearance of the damage was essentially the same for all three sizes of the erodent, and for two different substrate materials having different crystal structures.