Investigation of granular surface roughness effect on electrostatic charge generation

Electrostatic charge generation is a multivariable and complex issue whose working mechanism has never been fully understood. The objective of this paper is to investigate the effect of granule surface roughness on electrostatic charge generation. Two kinds of granule material, Polyvinyl chloride (PVC) and polypropylene (PP) were used with the granule size of 4 mm diameter, 2 mm height and the shape was cylinder or semi-cylinder. The working surfaces were grounded and roughness ranged from 0.140 to 8.600 μm. It was found that uneven surfaces tended to give rise to voids between two solids, where air stored in the voids was able to accelerate discharging. With the same roughness, PVC tended to generate more electrostatic charge than PP by one order of magnitude. For both materials, electrostatic charge generation first increased with surface roughness and then decreased. The maximum electrostatic charge generated was found to occur when the effects of interaction, contact area and voids discharging were at equilibrium. With the combined effect of humidity, surface roughness and contact area, highest electrostatics generation occurred near the mid-roughness tested in this work. Humidity had more effect on electrostatic charge generation as the granule working surface had lower roughness.     

The influence of surface diffusion on surface roughness and component distribution profiles during deposition of multilayers

The kinetic processes taking place on the surface and influencing the depth distribution of components during deposition of multilayers are considered by proposed kinetic model. The depth distribution of components in growing structure, broadening of interfaces between layers and shape of concentration peaks of multilayers are analyzed with respect of evolution of surface roughness during deposition. Surface roughness depends on adsorption rate and on surface diffusion. In presented model, the process of surface diffusion is subdivided into up-diffusion and down-diffusion. It is shown that atomic fluxes of up-diffusion and down-diffusion do not compensate each other even in the case of equal diffusion coefficients as they depend on coverage of different monolayers. Down-diffusion results in smoother surface, in contrary, up-diffusion makes it rougher. It is quantitatively shown by kinetic modeling that with increase of down-diffusion the amplitude of concentration peaks of components increases, the broadening of interface between layers decreases and concentration peaks become asymmetrical. The asymmetry of concentration peaks is found even in the case of equal diffusion coefficients of different components. At different diffusivity of components, the asymmetry is following: the concentration peaks of heavy-component (less diffusivity) show enhanced trailing tails on the back profile side (for light-component on the contrary). Up-diffusion results in increase of surface roughness and broadening of interface between layers. The quantitative functions of surface roughness on ratio of up- and down- diffusion coefficients are calculated and analyzed.     

An investigation into bacterial attachment to an elastomeric superhydrophobic surface prepared via aerosol assisted deposition

Bacterial attachment is highly dependent on a surfaces microstructure. For example, some rough surfaces provide grooves suitable for bacterial adhesion. Superhydrophobic surfaces with a Cassie-Baxter wetting mechanism are shown to prevent contact between a bacterium and surface attachment points. The surface used in this study is a highly rough thin film made from a silicone elastomer via an aerosol assisted chemical vapour deposition (AACVD) process. The films had water contact angles averaging 165°, a very low slip angle, and were capable of duplicating the Lotus effect. The ability of bacteria (Escherichia coli and Methicillin-resistant Staphylococcus aureus) to adhere to this surface was tested by submersion in a bacterial suspension. The superhydrophobic elastomer surfaces reduced the attachment of the bacteria tested, relative to the control surfaces of plain glass, and flat elastomeric films. The reduction in bacterial adhesion, without the external action of chemicals, gives the elastomer surface deposited with AACVD possible applications in biomedical and catering industries. This progressive study of bacterial adhesion is carried out on an AACVD prepared surface and presents adhesion results from both smooth and highly roughened elastomeric surfaces.     

Wavelet uniformity of plasma-processed surface roughness

A technique to characterize the nonuniformity of surface roughness (NSR) is presented. A discrete wavelet transformation (DWT) was used to quantitatively differentiate surface patterns. The technique was evaluated with the data collected from the etching of silicon oxynitride films in a C₂F₆ inductively coupled plasma. 3-D surface images were obtained by using atomic force microscopy. Vertical and lateral NSRs were investigated as a function of process parameters, including radio frequency source power, bias power, and pressure. The NSR data were correlated to experimental measurements of the surface roughness. It is noticeable that for any parameter variations there exist nearly identical NSRs. For each parameter variation, there was at least one specific NSR consistent with the surface roughness measurement. Selected NSRs can be utilized to monitor a variation in NSR and surface roughness simultaneously. Also, NSR may be more stringently optimized by controlling NSRs in a directional fashion.     

Effect of surface roughness on nanoindentation test of thin films

By using the two-dimensional quasicontinuum method, the nanoindentation process on a single crystal copper thin film with surface roughness is simulated to study the effect of surface morphology on the measurements of mechanical parameters. The nanohardness and elastic modulus are calculated according to Oliver-Pharr’s method. The obtained results show a good agreement with relevant theoretical and experimental results. It is found that surface roughness has a significant influence on both the nanohardness and elastic modulus of thin films determined from nanoindentation tests. The effect of such factors as the indenter size, indentation depth and surface morphology are also examined. To rule out the influence of surface morphology, the indentation depth should be much greater than the characteristic size of surface roughness and a reasonable indenter size should be chosen. This study is helpful for identifying the mechanical parameters of rough thin films by nanoindentation test and designing nanoindentation experiments.     

Effect of surface roughness on tribological properties of TiB2/Al composites

55 vol.% TiB₂/2024Al composites were fabricated by pressure infiltration method. The effect of surface roughness of GCr15 steel disc (Ra 0.606, 0.372, 0.023, 0.005 μm) on the tribological properties of composites was investigated. Results showed that with the change of surface roughness, there is an optimal value (Ra 0.023 μm) under which the friction coefficient and wear rate is the lowest. The optimal surface roughness is in the same order of mixture of TiO₂ and B₂O₃, observed on the surface of TiB₂ particles after pre-heating process. During sliding, the filling of this oxidation layer into the asperity gap of GCr15 and greatly reduces adhesion between aluminium and GCr15, furthermore, decreases the friction coefficient and wear rate.     

Slippery pores: anti-adhesive effect of nanoporous substrates on the beetle attachment system

Traction experiments with adult seven-spotted ladybird beetles Coccinella septempunctata (L.) were carried out to study the influence of surface structure on insect attachment. Force measurements were performed with tethered walking insects, both males and females, on five different substrates: (i) smooth glass plate, (ii) smooth solid Al₂O₃ (sapphire) disc, and (iii–v) porous Al₂O₃ discs (anodisc membranes) with the same pore diameter but different porosity. The traction force of beetles ranged from 0.16 to 16.59 mN in males and from 0.32 to 8.99 mN in females. In both sexes, the highest force values were obtained on smooth solid surfaces, where males showed higher forces than females. On all three porous substrates, forces were significantly reduced in both males and females, and the only difference within these surfaces was obtained between membranes with the highest and lowest porosity. Males produced essentially lower forces than females on porous samples. The reduction in insect attachment on anodisc membranes may be explained by (i) possible absorption of the secretion fluid from insect adhesive pads by porous media and/or (ii) the effect of surface roughness. Differences in attachment between males and females were probably caused by the sexual dimorphism in the terminal structure of adhesive setae.     

表面粗糙度对TiAl/AgCu/TiAl钎焊质量的影响

为探究表面粗糙度对钎焊质量的影响,在优选的钎焊温度870 ℃和保温时间5 min条件下,以AgCu合金为钎料,进行TiAl合金的真空钎焊,研究了表面粗糙度与磨痕方向对钎料润湿铺展、钎焊接头界面组织、力学性能的影响.采用扫描电镜、能谱分析、光学显微镜和万能材料试验机等分析测试手段,对钎焊接头的组织与力学性能进行分析.结果表明：AgCu钎料在各向异性的TiAl基板表面润湿铺展时会受表面特征影响,沿着特定的方向优先铺展,当基板表面不具各向异性特征时,钎料润湿铺展近似为圆形;表面粗糙度S_a=0.103 μm的基板,钎焊接头的平均剪切强度最优,达到323 MPa,而表面粗糙度S_a=0.133 μm的基板,接头平均剪切强度为245 MPa,钎焊接头强度均方差最大.     

Effect of initial surface topography on the surface status of LY2 aluminum alloy treated by laser shock processing

Samples manufactured by LY2 aluminum (Al) alloy with different initial surface topography were treated by laser shock processing (LSP), and then the surface topographies before and after LSP were carefully investigated with a non-contact optical profiler (NCOP). Moreover, the residual stress and microhardness were also examined. Results showed the following three aspects: (a) Initial surface topography will influence the surface roughness of LY2 when treated by LSP. The values of surface roughness of all the tested samples would tend to be stable after one LSP impact, and there was an ultimate value for the surface roughness after multiple LSP impacts, which was about 0.58 μm. (b) With the increase of initial surface roughness, the compressive residual stress decreased when subjected to one LSP impact. The surface residual stress of all the samples tended to be saturated after three LSP impacts, and the saturated value was nearly equal. (c) With the increase of initial surface roughness, the microhardness of all the samples increased when subjected to one LSP impact.     

Molecular effect on surface topography of GaN bombarded with PF4 ions

We study surface topography and thickness of GaN layers implanted at room temperature with 1.3 keV/amu F, P, and PF₄ cluster ions. Results show that the density of collision cascades has a dramatic effect on the surface roughness and the thickness of implanted layers. Surface roughness increases with increasing cascade density. For very dense cascades produced by PF₄ ions, the evolution of layer thickness is dominated by ion-induced sputtering. In contrast, for the case of P ions producing less dense cascades, ion-induced swelling is observed.     

The effect of fibre surface roughness on the mechanical behaviour of ceramic matrix composites

The interface between the matrix and the fibre plays an important role in controlling the strength and toughness of ceramic matrix composites. It has been found experimentally that depending on manufacturing process, the interface may show substantial surface roughness, which has been modelled analytically with certain degree of success. The analytical models, however, do not take into account the interface geometry. Instead, only the magnitude of the surface undulation is included. In this paper, a direct simulation of fibre–matrix interface roughness by the finite element method is performed on an axisymmetric unit cell with a fully debonded interface. The simulation is employed to account for the three dimensional stress state, surface roughness and interface friction, which are normally simplified or idealised in theoretical studies. The model gives the highly non-uniform interface shear and pressure, which have direct implications on the interface damage and composite behaviour. Under the approximation made in the model, the positive transverse strains does not show up in the simulation despite the fact that two different surface roughness are used.     

基于散斑强度相关函数的表面粗糙度测量方法

激光经过被测表面反射和散射后,通过自由空间传播至观察面上形成散斑图像,其统计分布依赖于被测表面的微观形貌。分析此散斑图像的二阶统计特性,导出了强度变化的相关函数和表面粗糙度参数之间的关系。以表面粗糙平均值Ra分别为0.1靘, 0.2靘, 0.4靘和0.8靘的平磨标准金属样块形成的散斑图像为例,根据强度变化相关函数的离散化定义,计算得到该相关函数值。结果表明,表面越粗糙,散斑越分散,强度变化的相关函数波动越大。因此,该参数可以反映不同的粗糙面,用其作为表征表面粗糙度的特征参数,扩大了测量范围。该方法实验系统简单,对于实际测量环境要求不高,对震动不是非常敏感,适于在线测量。     

An experimental investigation as to the effect of cutting parameters on roundness error and surface roughness in cylindrical grinding

This paper presents the results of an experimental investigation as to the effects of grinding parameters on roundness error and surface roughness in cylindrical grinding. Many variables including the wheel materials, wheel loading and dressing, workpiece metallurgy, work drive mechanisms, work holding methods, coolant types, feeds and speeds, machine stiffness and age, surface conditions, centre conditions, floor vibrations all influence the quality of ground parts. However, the composite sum of these grinding parameters creates static and dynamic forces. It is obvious that the roundness error and surface roughness are created by many parameters, but in this study, only the effects of the depth of cut, work speed and feed rate which create the grinding forces in cylindrical grinding are investigated. The grinding experiments were planned according to the principles of orthogonal arrays (OAs), developed by Taguchi, and were performed so as to understand the effects of these parameters on roundness error and surface roughness. The experimental data was analysed by using statistical tools: the percent contribution from an analysis of variance (ANOVA) and the correlation between machining parameters with roundness error (R) and also surface roughness (Ra). Roundness was found to be the most related with the cutting speed, grinding force and depth of cut, while surface roughness is related to feed rate and work speed.     

Effects of thermal debinding on surface roughness in micro powder injection molding

Micro metal injection molding (μMIM) is a promising process for the replication of metallic microstructures. In the micrometer regime, surface roughness is important in view of the dimensional tolerance and the applications of microstructured parts. In this paper, the effects of debinding on the surface roughness of 316 L stainless steel microstructured parts were investigated. Experimental results showed that using higher heating rates during debinding increased the weight loss of debound parts. The debound parts of higher weight loss gave better surface finish after sintering. Comparing the increase of sintering time and temperature, the surface finish improvement was more significant for increasing temperature.     

Theoretical and empirical coupled modeling on the surface roughness in diamond turning

In this work, a theoretical and empirical coupled method is proposed to predict the surface roughness achieved by single point diamond turning, in which the surface roughness is considered to be composed of the certain and uncertain parts. The certain components are directly formulated in theory, such as the effects of the kinematics and minimum undeformed chip thickness. The uncertain components in relation to the material spring back, plastic side flow, micro defects on the cutting edge of diamond tool, and others, are empirically predicted by a RBF (radial basis function) neural network, which is established by referring to the experimental data. Finally, the particle swarm optimization algorithm is employed to find the optimal cutting parameters for the best surface roughness. The validation experiments show that the optimization is satisfied, and the prediction accuracy is high enough, i.e. that the prediction error is only 0.59–10.11%, which indicates that the novel surface roughness prediction method proposed in this work is effective.     

A fatigue crack initiation model incorporating discrete dislocation plasticity and surface roughness

Although a thorough understanding of fatigue crack initiation is lacking, experiments have shown that the evolution of distinct dislocation distributions and surface roughness are key ingredients. In the present study we introduce a computational framework that ties together dislocation dynamics, the fields due to crystallographic surface steps and cohesive surfaces to model near-atomic separation leading to fracture. Cyclic tension–compression simulations are carried out where a single plastically deforming grain at a free surface is surrounded by elastic material. While initially, the cycle-by-cycle maximum cohesive opening increases slowly, the growth rate at some instant increases rapidly, leading to fatigue crack initiation at the free surface and subsequent growth into the crystal. This study also sheds light on random local microstructural events which lead to premature fatigue crack initiation.     

Effect of chemical treatment on tensile strength and surface roughness of 3D-printed ABS using the FDM process

Fused deposition modelling (FDM) is one of the most commonly used additive manufacturing processes because of its environment-friendly nature and cost-effectiveness. However, it suffers badly from low surface quality due to a larger layer resolution. The surface finish of FDM parts can be enhanced by post chemical treatment using various solvents. The chemical treatment reduces the surface roughness by dissolving the external surfaces of 3D-printed samples. Chemical treatment is an easy, fast and economical technique. In the present investigation, the effect of chemical treatment on surface roughness and tensile strength of acrylonitrile butadiene styrene (ABS) parts made using the FDM process is investigated using two chemicals, namely acetone and 1, 2 dichloroethane. The post chemical treatment dramatically improves the surface finish and dimensional accuracy of ABS specimens. But chemical treatment results in the reduction of the tensile strength. Better tensile strength is obtained while using acetone solvent and a better surface finish is obtained using dichloroethane.     

The influence of nanosized precipitates on Portevin-Le Chatelier bands and surface roughness in AlMgScZr alloy

The influence of different precipitate-dislocation interactions,namely dislocation shearing and bypass-ing mechanisms,on PLC bands and the resultant surface roughness in AlMgScZr alloy was investigated.Three-dimensional surface roughness was quantitatively measured by confocal microscopy.We find that the introduction of shearable precipitates increases the stress amplitude,decreases the PLC bands number and surface roughness.However,the stress amplitude decreases,the PLC bands number and sur-face roughness increase with shearable precipitates turning to nonshearable precipitates.By analyzing the precipitation strengthening mechanisms quantitatively,the influence of precipitates on PLC bands and the resultant surface roughness was explored.Furthermore,our study demonstrates that the shear-able precipitates can decrease the surface roughness by decreasing the number of PLC bands,which is instructive for designing structural materials with desirable mechanical property and surface quality.     

Atomic-scale cellular model and profile simulation of Si etching: Formation of surface roughness and residue

Formation mechanisms for profile anomalies such as surface roughness and residue have been investigated numerically and experimentally for Si etching in Cl₂/O₂ plasmas. The numerical simulation employed an atomic-scale cellular model (ASCeM) based on the Monte Carlo algorithm, which reproduced the feature profile evolution experimentally observed during etching at increased O₂ concentrations. A comparison between simulation and experiment indicated that the local surface oxidation induces surface roughness at the bottom of the feature during etching; then, synergistic effects between surface oxidation and ion scattering in microstructural features on roughened surfaces increase the surface roughness, which in turn causes a number of significant residues or micropillars on bottom surfaces of the feature. In practice, in roughened microstructural features, geometrical shadowing effects for neutral oxygen suppress the surface oxidation at the local feature bottom, where the energetic ion incidence is increased owing to ion scattering on sidewalls of the local feature.