Surface Formation Mechanism Research Articles

Effect of crack propagation on surface formation mechanism and surface morphology evaluation of longitudinal–torsional composite ultrasonic mill grinding of Si3N4

Crack propagation is critical in determining the surface forming process and machined surface quality of hard brittle materials. However, there is still a lack of research on this subject. In this work, the effect of crack propagation on the surface formation mechanism and surface morphology of silicon nitride ceramics was investigated via longitudinal–torsional composite ultrasonic-assisted mill grinding, and a reconstruction model of the machined surface morphology considering crack propagation was proposed. This model was quantitatively characterized and evaluated by the average roughness Sa and the kurtosis Sku. It was found that the simulation results considering crack expansion are in good agreement with the experimental results. The average relative errors in the average roughness and kurtosis were found to be 7.95% and 9.46%, respectively. A primary effect analysis was performed to understand the influence of the process parameters on the machined surface morphology. It was found that ultrasonic vibrations lead to changes in the shear angle and shear velocity of abrasive grains, thereby changing the machined surface morphology. The results presented here provide a practical method for predicting and controlling the machined surface quality during precision machining of ceramic materials.

Experimental Investigation on the Surface Formation Mechanism of NdFeB during Diamond Wire Sawing

Diamond wire sawing is widely used in processing NdFeB rare earth permanent magnets. However, it induces periodic saw marks and fracture chipping pits, which severely affect the flatness and surface quality of the products. In this study, the lateral motion of the diamond wire was monitored to determine the surface formation mechanism. Then, a white light interferometer and an SEM were used to observe the sawed surface profile. Finally, the surface quality was quantitatively studied by identifying the area rate of fracture chipping pits with an image recognition MATLAB script. According to the observation results, the calculation formula of PV which is related to the process parameters was deduced. Additionally, by combining the fracture rate and wire vibration, a novel method was proposed to investigate the optimal process parameters. It can be found that the surface quality sawed at P = 0.21 MPa, vf = 0.2 mm/min, and vs = 1.8 m/s remains better than when sawed at P = 0.15 MPa, vf = 0.1 mm/min, and vs = 1.8 m/s, which means the sawing efficiency can be doubled under such circumstances, i.e., when the surface quality remains the same.

Influence of Coal Mining on Historical Buildings: Case Study in Shanxi

Numerous historical buildings exist in Shanxi Province, a major coal producing area in China, so there exist many overlapping areas between ancient wooden buildings and coal mining. Coal mining in overlapping areas will lead to surface subsidence, which will have an impact on historical buildings. Based on the distribution of historical buildings and the distribution and mining of coal resources in Shanxi Province, this paper concludes that the overlapping areas of coal mining and ancient wooden buildings in Shanxi Province are mainly concentrated in Changzhi City, and the Lu'an mining area in Changzhi City is selected as the research object. In addition, using the gray correlation analysis method, the surface subsidence coefficient, which characterizes the intensity of mining subsidence, is used as the reference sequence. Seven factors selected from the geological conditions and mining conditions of the Lu'an mining area are used as the comparison sequence to calculate the gray correlation between each influencing factor and the surface subsidence coefficient, and to obtain that geological factors such as the nature of the overlying rock layer, bedrock thickness and dip angle of the coal seam, and mining factors such as mining height, average mining depth and working face size largely determine the surface subsidence coefficient. The surface subsidence in the overlap area could largely be influenced by geological factors such as the nature of the overlying rock layer, bedrock thickness and coal seam inclination, and mining factors such as mining height, average mining depth and working face size. Finally, we investigate the possible effects of surface subsidence on ancient wooden buildings in the overlapping area with the surface subsidence and formation mechanism and propose technical measures to reduce the effects of surface subsidence due to coal mining on historical buildings in the overlapping area.

Effect of cavitation on surface formation mechanism of ultrasonic vibration-assisted EDM

Effect of cavitation on surface formation mechanism of ultrasonic vibration-assisted EDM

Surface and subsurface formation mechanism of SiCp/Al composites under ultrasonic scratching

Rotary ultrasonic machining (RUM) is an effective method of high-quality and high-efficiency machining for advanced composites. However, the machining mechanism and kinematic characteristics of ultrasonic machining of SiC particles-reinforced aluminum matrix (SiC p /Al) composites are yet unclear, limiting the applications of RUM in composites machining. In this study, a rotary ultrasonic vibration-assisted scratch (RUVAS) test was designed for the high-volume fraction of SiC p /Al composites. The kinematic and scratch force model of RUVAS was developed to describe the scratch process of SiC p /Al. Both RUVAS and conventional scratch (CS) tests were performed under various scratch speeds on SiC p /Al. The scratch trajectory was divided into three modes: continuous, semi-continuous, and intermittent. We observed the formation of different surface morphology under different modes. The scratch force difference between RUVAS and CS was insignificant when the scratch speed is high, which indicated that the effect of ultrasonic vibration diminished at a high speed when the ultrasonic frequency was fixed. When assisted by ultrasonic vibration, the scratch morphology of SiC p /Al indicated that the matrix has undergone significant plastic deformation. While the hard SiC particles tended to be ruptured and pressed into the plastic matrix, this mechanism can effectively suppress the initiation and propagation of cracks, which is beneficial to reducing the stress influence zone, healing the surface defects, and improving the surface integrity. The subsurface morphology indicates that the subsurface damage under CS and RUVAS mainly includes particle cracking, matrix tearing, and interface failure. Our experimental result shows that ultrasonic vibration can effectively reduce the subsurface damage of SiC p /Al composites, bringing insight into fundamental mechanisms of ultrasonic machining and providing guidance for the vibration-assisted processing of SiC p /Al composites.

Straightforward FeOOH nanografting of Al-based SrTiO3 perovskite material as core–shell nanoflower-like heteronanostructure with enhanced solar light-driven photodegradation capability

Extensive attention and considerable efforts have been made to construct efficient heterogeneous nanoparticulate systems for surface chemical reactions to be active in solar light-driven photodegradation. This work addresses current deficiencies of the nanoparticles-focused systems intended for visible light photodegradation by developing a newly-formulated innovative chemically-engineered multi-component system that functions as a recyclabe, nontoxic, active and inexpensive catalyst for photodegradation of tetracyclne antibiotic. Here, we show a straightforward FeOOH nanografting of Al-based SrTiO3 perovskite material as core–shell nanoflower-like heteronanostructure with enhanced solar light-driven photodegradation capability over harmful antibiotics. A persuasive surface formation mechanism is proposed based on systematic investigation of the assembly process. In-depth caracterization of structural, optical and morphological properties of the prepared samples was investigated using a series of complementary analytical techniques, such as XRD, FE-SEM, HR-TEM, synchrotron XPS, as well as hard and soft XAS in both total electron yield (TEY) and fluorescence yield (TFY). The oxygen-deficient nature of core and shell interface indicates its n-doping and the availability of free charges in core which can be either transferred to the shell or create localized absorption levels into the valence band. This study provides a real opportunity to rationally photocatalysts design with very promising performance in water treatment.

Study on the Erosion Morphology of Cohesive Soil under the Vertical Impact of a High-Pressure Moving Water Jet

In the in situ leaching process of ionic rare earth ore, high-pressure moving water jet technology has been applied to improve floor leakage problems. However, it has been found that the morphology of the erosion surface formed by a moving water jet cannot be accurately predicted. The range of the erosion surface has an important influence on the stability of liquid collection engineering and the liquid collection rate of rare earth resources, which is an important basis for the design of liquid collection engineering. To study this, soil-breaking tests using high-pressure moving water jets for a Pingnan mine were conducted. The influences of jet pressure and nozzle moving speed on soil-breaking morphology were analysed. The mechanism of erosion surface formation was revealed by erosion theory, and a method of predicting the erosion surface geometry based on jet pressure and nozzle speed is proposed. The results show that, in the jet pressure range of 5~10 MPa, with increases in jet pressure and decreases in nozzle speed, the geometric shape of the erosion surface tends to expand, and these parameters have no effect on the morphological characteristics of the erosion surface. In the soil-breaking process, the erosion speed decreases with increases in jet distance. As the nozzle speed becomes greater, the degree of the attenuation of erosion speed at a given jet pressure also becomes greater. Soil-breaking depth has a quadratic relationship with jet pressure and a 0.5 power function relationship with nozzle speed. The geometry of the erosion surface has self-similarity and can be divided into straight and curved sections. Accordingly, an empirical formula of the erosion surface geometric shape is proposed. The error of predicting the soil-breaking depth is less than 11%, which can provide a reference for engineering applications.

Acrylonitrile Butadiene Polystyrene–SiO2 Composite Nanostructures for Self-Regulated Superhydrophobic Liquid Dosage Systems

Superhydrophobic coatings are widely studied for fluid regulation due to their water-repellent surface characteristics. However, there are not many reports on fluid behavior when it flows from a region of higher wettability to that of lower wettability. A fundamental understanding of such behavior would be very useful for regulating the fluid flow through a superhydrophobic channel. Therefore, this work focused on the fabrication of superhydrophobic nanostructured coatings inside fine cylindrical channels and the investigation of the fluid flow behavior through them. The superhydrophobic SiO2 coatings were obtained through an ultrasound-assisted one-step immersion technique. A self-stratified mechanically durable conformal superhydrophobic coating was obtained inside millimeter-sized fine 3D structures. A binder-free precursor solution has low viscosity and thereby enhances the penetration of the solvent into the polymer surface through ultrasonication. The self-stratification-based surface formation mechanism was explained using scanning electron microscopy images. The fluid behavior inside the superhydrophobic channels was experimentally investigated by analyzing the flow through the hollow cylindrical superhydrophobic channels. Experiments were conducted for different channel lengths (l) and radii (r), and mathematical formulations were developed to determine the maximum pressure (Pmax) that the superhydrophobic cylinders could hold when the fluid inside the channel was under static equilibrium. Finally, a self-regulated fluid delivery system was postulated based on the experimental and theoretical findings.

Mathematical Modeling and Experimental Validation of Surface Roughness in Ball Burnishing Process

Burnishing is a cold working technique used as a surface enrichment to meet the desired surface properties of the workpiece. It improves the visual properties, dimensional tolerances, fatigue strength, surface roughness, and hardness of the work material by applying appropriate pressure through a complex ball burnishing tool to cause plastic deformation. In the current work, the mathematical modeling of the burnishing process was carried out to predict surface roughness by considering the process parameters such as contact radius, penetration depth, and elastic rebound. Further, a customized tungsten carbide (W.C.) insert having a hardness of 80 HRC was developed for the burnishing operation. The micro-hardness of the resulting burnished surface improved from 44 to 48 HRC. The surface quality of the tungsten carbide insert improved by up to 17.1 nm through polishing. Several experiments were performed by selecting appropriate process parameters using developed model feedback. The surface quality of the workpiece improved by up to 45 nm, which resulted in automatic improvements in fatigue strength up to seven times that of the virgin material. The results predicted from the mathematical model were in good agreement (less than 5% deviation) with the experimental results. This study helps to understand the surface formation mechanism in the burnishing process in more detail. Additionally, the achieved results show a significant improvement in the surface finish (~95%), indicating the potential of the burnishing process and how fast and cost-effective it is. The novelty of this paper lies in the improvement in surface roughness and the validation of our mathematical model results with the experimental results.

Investigation on the surface formation mechanism in scratching of CFRP composites with different fiber orientations

Rotary ultrasonic machining (RUM) is an effective approach to process carbon fiber reinforced polymer (CFRP) composites. However, the surface formation mechanisms in RUM for different fiber orientations have not been comprehensively investigated. In this research, ultrasonic vibration-assisted scratching (UVAS) and conventional scratching (CS) tests with invariant cutting depth were conducted innovatively to expose the material removal mechanism. Based on the kinematics analysis, the characteristics of material removal process have been compared between UVAS and CS, and dynamic changes of actual cutting angle with the addition of ultrasonic vibration have been studied for the first time. The groove morphologies and scratching loads were analyzed for different fiber orientations and scratching parameters. The experimental results revealed that the fracture mode of fiber was principally decided by cutting angle. And the surface crack propagation can be significantly inhibited in UVAS due to the intermittent cutting behavior, increase of instantaneous velocity and the dynamic alteration of direction and magnitude of actual cutting angles. This research will help enable an in-depth understanding of the material removal mechanism of CFRP composites in RUM, and is beneficial for the optimum utilization of vibration assisted processing for advanced composites.

A study investigating the cutting mechanism of compacted graphite iron based on a novel microstructure of finite element model

Compacted graphite iron is internationally recognized as a material that has the potential to be applied for preparing high performance engine components. However, difficulties during machinability seriously limit the mass production of these. A novel method based on MATLAB image recognition and python programing was used to establish a microstructural model that included graphite and pearlite particles. The thermal conductivity and specific heat capacity at different temperatures was measured and the results were used to validate the model. Using this novel model, the chip morphology and formation mechanism, cutting surface morphology and formation mechanism and cutting temperature distribution were studied. The simulation results show that crack formation on the chip surface and generation of graphite fragments occurs during the cutting process. The crack opening angle during this is approximately 33°. Significant graphite cavities also appeared on the cutting surface. The stress concentration at the boundary of graphite and pearlite during cutting process was analyzed, and demonstrated to be the primary reason for these phenomena. The temperature of both the rake face and flank face are simulated with the highest cutting temperature concentrated in the secondary deformation zone reaching approximately 322 °C. Furthermore, the simulation results are consistent with the experimental results.

Surface integrity and material removal mechanisms in high-speed grinding of Al/SiCp metal matrix composites

SiC particle reinforced Al metal matrix composites (Al/SiCp MMCs) are typical difficult-to-machine materials due to the heterogeneous constituent. Poor surface integrity is commonly caused in conventional machining methods. To explore material removal mechanisms in high-speed grinding, this study carries out high-speed grinding (HSG) on an Al/SiCp MMC at a grinding speed from 30.4 m/s to 307.0 m/s, and assesses surface integrity including surface damage and subsurface damage (SSD) to explore how different grinding speeds take effect therein. The results reveal that improved surface quality is attained in HSG in which continuous and discontinuous dynamic recrystallization mechanisms govern Al grain refinement, and the latter is inclined to occur in the upper part of the ground surface. The distribution of the O-rich zone is closely associated with subsurface cracks. The workpiece ground at a higher grinding speed is with less damage than at a lower grinding speed due to the reduced O-rich zone. Three different layers in the subsurface below ground workpiece are identified based on various features, which are relatively narrower compared to that in low-speed grinding. The range of plastic deformation of the Al alloy matrix is suppressed in HSG because of larger Al grains and a reduced depth of lateral cracks in Al alloy matrix. Distinctly denser dislocation kinks formed at the boundary of SiC particles in HSG indicate the increased ductility of SiC particles. In HSG of Al/SiCp MMCs, strain-rate effect prevails for Al alloy matrix as a result of reduced ductility, and size effect plays the dominant role for SiC particles due to increased ductility, which facilitate reducing the property discrepancies between these two very different components. Therefore, an improved surface integrity of the Al/SiCp MMCs is realized through HSG. This study enhances the understanding of the surface and subsurface formation and material removal mechanisms in HSG of Al/SiCp MMCs, which can provide a theoretical basis and practical reference for achieving better surface quality for Al/SiCp MMCs and other composites machined by HSG.

Experimental and Theoretical Investigations on Diamond Wire Sawing for a NdFeB Magnet

The normal processing of sintered NdFeB magnets, used in many applied fields, involves diamond wire sawing. Due to the fact of its relatively lower hardness and high brittleness, the surface roughness and periodic waviness of the sawed surface have become a serious problem, but the surface formation mechanism is still unknown. In this work, a diamond wire sawing experiment with a NdFeB magnet was conducted while both the cutting force and the diamond wire lateral displacement were monitored. The vibration, the lateral swing of the wire and the cutting force were thoroughly analyzed. After the experiment, the surface morphology was carefully inspected under both a white light interferometer and SEM. It was discovered that the lateral swing of the diamond wire was the main cause of the periodic waviness on the surface, the PV of which was positively proportional to the normal cutting force. The surface morphology and surface roughness along the saw mark revealed that the vibration impact of ploughing/rubbing grits can induce the NdFeB grain to loosen off and cause more brittle fractures when the feed rate was 0.05 mm/min under wet cutting.

Formation mechanism of the distinctive granular fracture surface in subsurface fracture of Ti6Al4V alloy

The formation mechanism of the granular regions often observed in subsurface fractures of Ti6Al4V alloy was experimentally investigated. To simulate and simplify the phenomenon of crack opening and closure, which is strongly related to fatigue crack propagation and strength properties, uniaxial cyclic compression tests were conducted in air and vacuum using test pieces with rounded surfaces under contact conditions. The results showed ring-like patterns on the parts of the rounded surfaces subjected to cyclic contact regardless of the ambient environmental conditions. However, in the case of vacuum only, fine surface asperities were observed, which were quite similar to those in the subsurface fractures. Microstructural refinement was confirmed by cross-sectional observation of the concave and convex parts. In the refined microstructure, voids and cracks were observed, which were formed during the refinement and adhesion processes. Microstructural refinement and metallic adhesion under compression loading in vacuum are key phenomena for the formation of fine surface asperities. Based on the experimental results, a new model for the formation mechanism of the granular region was proposed. This model can explain the characteristics of the granular region and the properties of subsurface fractures, which occur at lower stress and have longer lifetimes than surface fractures.

Formation Mechanism of Dkdp Surface in Single Point Diamond Fly-Cutting Process and the Resulting Degradation of Laser-Induced Damage Performance

Formation Mechanism of Dkdp Surface in Single Point Diamond Fly-Cutting Process and the Resulting Degradation of Laser-Induced Damage Performance

Analysis of Surface Residual Stress and Formation Mechanism of Metamorphic Layer in PCBN Tool Cutting Superalloy under High-pressure Cooling

Analysis of Surface Residual Stress and Formation Mechanism of Metamorphic Layer in PCBN Tool Cutting Superalloy under High-pressure Cooling

Study on the Formation Mechanism of Surface Adhered Damage in Ball-End Milling Ti6Al4V.

Ball-end cutters are widely used for machining the parts of Ti-6Al-4V, which have the problem of poor machined surface quality due to the low cutting speed near the tool tip. In this paper, through the experiments of inclined surface machining in different feed directions, it is found that the surface adhered damages will form on the machined surface under certain tool postures. It is determined that the formation of surface adhered damage is related to the material adhesion near the cutting edge and the cutting-into/out position within the tool per-rotation cycle. In order to analyze the cutting-into/out process more clearly under different tool postures, the projection models of the cutting edge and the cutter workpiece engagement on the contact plane are established; thus, the complex geometry problem of space is transformed into that of plane. Combined with the case of cutting-into/out, chip morphology, and surface morphology, the formation mechanism of surface adhered damage is analyzed. The analysis results show that the adhered damage can increase the height parameters Sku, Sz, Sp, and Sv of surface topographies. Sz, Sp, and Sv of the normal machined surface without damage (Sku ≈ 3) are about 4–6, 2–3, and 2–3 μm, while Sz, Sp, and Sv with adhered damage (Sku > 3) can reach about 8–20, 4–14, and 3–6 μm in down-milling and 10–25, 7–18, and 3–7 μm in up-milling. The feed direction should be selected along the upper left (Q2: β ∈ [0°, 90°]) or lower left (Q3: β ∈ [90°, 180°]) to avoid surface adhered damage in the down-milling process. For up-milling, the feed direction should be selected along the upper right (Q1: β ∈ (−90°, 0°]) or upper left (Q2: β ∈ [0°, 90°)).

Fabrication of three-dimensional sin-shaped ripples using a multi-tip diamond tool based on the force modulation approach

A novel cutting strategy of machining microstructure surface with the multi-tip diamond tool based on the force modulation approach is proposed in this paper. The multi-tip diamond tool with periodic sinusoidal microstructures was prepared by focused ion beam technique. The influence of applied cutting forces on the depths of cut and material removal states was investigated experimentally. MD simulations revealed a significant phenomenon of no material side flow when using the multi-tip diamond tool cutting on single crystal copper substrate. The movement of stacking faults, Lomer-Cottrell locks and Hirth locks jointly governed the formation mechanism of machined surface. To demonstrate the feasibility and effectiveness of this proposed cutting strategy, the fabrication of periodic sinusoidal microstructures under constant forces was successfully realized on the microsphere surface. Furthermore, three-dimensional sin-shaped ripples required variable forces controlling were achieved with high-precision surface quality. The cross-sectional topography of obtained ripples matched the geometry of used MTD tool quite well. In particular, the processing parameters, including the time period of loading forces and cutting speeds, determine the expected wavelength of ripples and play a central role in the surface machining accuracy.

Influence of the fiber orientation on 3D C/C–SiC composite material and its formation mechanism of the machining surface

Influence of the fiber orientation on 3D C/C–SiC composite material and its formation mechanism of the machining surface

Aluminum dispersed bamboo activated carbon production for effective removal of Ciprofloxacin hydrochloride antibiotics: Optimization and mechanism study

The central composite rotatable design (CCD) of response surface methodology (RSM) was used to optimize aluminum dispersed bamboo activated carbon preparation. The independent variables selected for optimization are activating agent (AlCl3) concentration (mol/L), activation temperature (°C), and activation time (min.). The independent variable's response change was observed through the percentage adsorption efficiency of Ciprofloxacin hydrochloride (CIP) antibiotics. The maximum CIP adsorption efficiency was found to be 93.6 ± 0.36% (13.36 mg/g) for the adsorbent prepared at AlCl3 concentration 2.0 mol/L, activation temperature 900 °C, and activation time 120 min. The adsorption efficiency was recorded at the natural pH (7.9) of the adsorbent (3 g/L)-adsorbate (50 mL solution of 50 ppm) mixture. The Al-dispersed bamboo activated carbon was characterized for its surface morphology, surface elemental compositions, molecular crystallinity, surface area, pore morphology, and surface functional groups. The mechanism of adsorbent surface formation and CIP adsorption sites were explored. The characterization data and mechanism study will help in deciding possible future applications in other fields of study.