Changes In Surface Profile Research Articles

Effect of sediment erosion on pressure pulsations in a large Pelton turbine

AbstractPelton turbines functioning in sandy river environments often encounter difficulties due to the swift movement of sediment particles, leading to erosion and damage to overflow components. These challenges can result in operational instability, particularly noticeable in large turbines. Pressure pulsation is crucial for turbine stability, and alterations in overflow component profiles caused by sediment erosion can worsen pressure pulsations. This study utilizes numerical simulations to analyze turbine pressure pulsations based on surface profile changes of runner buckets after 2 and 4 years of sediment erosion in a single 500 MW large‐scale Pelton turbine. Our findings reveal that erosion leads to a gradual decrease in pressure pulsation along the bucket's splitting edge from the notch to the root. After 4 years of erosion and wear, the relative pressure pulsation amplitude in the root region increased by more than 530%. Additionally, changes occur in the thickness of the water film in the erosion area on the working surface, disrupting the flow pattern and generating more vortices. This occurrence intensifies the relative pressure pulsation amplitude and reduces bucket stability. The study findings highlight the significant impact of sediment erosion on Pelton turbine pressure pulsation, posing a considerable risk to the unit's operational stability and safety.

Observation of Surface Profile Change and Estimation of Contact Area Ratioin High Contact Pressure Tests of Small Pure Aluminum Blocks

Observation of Surface Profile Change and Estimation of Contact Area Ratioin High Contact Pressure Tests of Small Pure Aluminum Blocks

Evolution mechanism of the rough surface in vibratory finishing within restricted space

ABSTRACT Vibratory finishing within restricted space is an effective way to finish the surface of complex cavities in an aero-engine integral casting casing, where the contact mechanism between the processing media and the rough surface is the nature for producing the processing effect. In this work, vibratory finishing was performed by semi-shading the workpiece, comparing the workpiece surface profile change with time for different vibration directions and processing positions, and height parameters and feature parameters evaluated the rough surface. The results show that the process of profile change on the workpiece mainly subjected to normal action is mainly the raising of valleys after profile peaks extrusion deformation and accompanied by the formation of finer peak-to-valleys. The workpiece subjected to tangential action reduces the surface roughness by filling the valleys after cutting the peak tips. The finishing mechanisms for rough surfaces can be summarized as collision, roll-pressing, and scratching.

Surface roughness effects on electrochemical anodization behavior of binderless tungsten carbide and oxide boundary generation

Electrochemical anodization has been utilized to reduce the surface hardness of Tungsten Carbide (WC) so that to increase its machinability. In this study, experiments have been conducted to illustrate the impact of surface roughness on electrochemical anodization of binderless WC. Anodization was performed on binderless WC that had different surface roughness by applying a constant voltage and utilizing Sodium Hydroxide (NaOH) as the electrolyte. Oxide generation mechanism during the anodization process has been analyzed in detail, through the investigation of current behavior, surface characterization, surface hardness reduction, surface profile change. It has been observed that during the anodization process, multiple peaks in current curves were produced as a result of discharge channels, induced by the cavities at oxide-substrate interface. When the electric barrier is broken, there was an increase in the formation of oxide layers. Hardness decreased significantly across all substrate conditions. Pristine WC substrate had a robust hardness of 33.34 GPa, while non-polished, semi-polished, and polished substrates had 8.26, 9.545, and 9.411 GPa, respectively. These findings demonstrate the significant impact of anodization on WC's mechanical characteristics, resulting in a 71.6 % decrease in hardness across substrate states. A hypothesis has been presented to describe the overall anodization behavior and boundary oxide generation mechanism of binderless WC. Polished WC substrates have lower surface roughness, indicating more controlled and homogeneous anodization as compared to non-polished and semi-polished WC substrates. The present study enhances the understanding of the impact of surface roughness on the electrochemical anodization of binderless WC, which will further facilitate its incorporation with machining techniques.

Influence of Dynamic Strain Sweep on the Degradation Behavior of FeMnSi-Ag Shape Memory Alloys.

Iron-based SMAs can be used in the medical field for both their shape memory effect (SME) and biodegradability after a specific period, solving complicated chirurgical problems that are partially now addressed with shape-memory polymers or biodegradable polymers. Iron-based materials with (28-32 wt %) Mn and (4-6 wt %) Si with the addition of 1 and 2 wt % Ag were obtained using levitation induction melting equipment. Addition of silver to the FeMnSi alloy was proposed in order to enhance its antiseptic property. Structural and chemical composition analyses of the newly obtained alloys were performed by X-ray diffraction (confirming the presence of ε phase), scanning electron microscopy (SEM) and energy-dispersive spectroscopy. The corrosion resistance was evaluated through immersion tests and electrolyte pH solution variation. Dynamic mechanical solicitations were performed with amplitude sweep performed on the FeMnSi-1Ag and FeMnSi-2Ag samples, including five deformation cycles at 40 °C, with a frequency of 1 Hz, 5 Hz and 20 Hz. These experiments were meant to simulate the usual behavior of some metallic implants subjected to repetitive mechanical loading. Atomic force microscopy was used to analyze the surface roughness before and after the dynamic mechanical analysis test followed by the characterization of the surface profile change by varying dynamic mechanical stress. Differential scanning calorimetry was performed in order to analyze the thermal behavior of the material in the range of -50-+200 °C. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) along with Neaspec nano-FTIR experiments were performed to identify and confirm the corrosion compounds (oxides, hydroxides or carbonates) formed on the surface.

On erosion transition from the incubation stage to the accumulation stage in liquid impingement erosion

The evolution of surface profiles during erosion caused by the continuous impact of a liquid jet was studied using a water-jet apparatus. In this study, we focused on the erosion transition from the incubation stage to the accumulation stage during liquid impingement erosion, which is important for water-jet cleaning and aging management for nuclear power plants. By computing the local erosion rate distribution and surface roughness parameters, the formations of isolated pits and asperities were investigated. The structure of erosion caused by liquid impingement was extracted by using a dynamic mode decomposition technique. The surface profile changes were primarily caused by the formation of isolated pits and asperities during the incubation stage. The roughness parameters remained unchanged during the incubation stage, with barely measurable erosion depth, whereas the skewness of the surface profile began to increase during this stage. The initial erosion with a small-scale roughness gradually evolved into a large-scale crater. Dynamic mode decomposition analysis showed the presence of a short-wavelength (mode A) surface depression during the incubation stage, followed by a long-wavelength (mode B) erosion crater caused by the merging of mode A surface depressions during the accumulation stage.

Effects of gravity on the capillary flow of a molten metal

Repair and construction in space by means of brazing requires understanding of the effect of gravity on the capillary flow of a molten metal. We perform two sets of experiments: (1) spreading of a sessile drop of liquid aluminum-silicon-flux (Al-Si-KxAlyFz) composite braze on a horizontal alumina (Al2O3) substrate (a non-wetting surface), and (2) capillary flow of the same braze alloy on an inclined aluminum-manganese (AA3003) substrate (a wetting surface). We vary the mass of the brazing liquid and the inclination of the substrate (i.e., the relative direction of gravity).In the composite metal/flux sessile drop experiments, we observe a secondary liquid flux meniscus forming at the contact line between the liquid Al-Si and the alumina substrate. We demonstrate that the equilibrium contact angle appears to be close to 180°, while the apparent contact angle depends on the mass of the braze. In the second set of experiments, we study the molten braze alloy on different inclinations of AA3003 in a wedge-T wetting/non-wetting assembly. As the inclination angle decreases, the wetting distance increases and the surface profile changes from a non-symmetric bag-like shape to a more symmetric pancake shape. With the mass decreasing, the surface profile on the vertical substrate approaches a symmetric shape when the wetting distance is equal or smaller than the capillary length. While the non-homogeneous melting and hence, the non-homogeneous microstructure of the melt, may prevent a full symmetry. Computational predictions of equilibrium shapes are in good agreement with experimental results.

Investigation of effect of logjam series for varying channel and barrier physical properties using a sparse input data 1D network model

Targeted design and placement of natural flood management leaky barriers, or engineered logjams, and accurate representation of logjams in hydraulic models across different scales is necessary to generate desired water storage and flood peak attenuation for effective river restoration and natural flood management projects. We systematically assess the effect of varying logjam spacing, extent of logjam-generated change in water surface profile, vertical height of lower gap, overflow to local floodplain, and varying channel slope, representing a series of logjams in a sparse input data 1D network model including the jam-generated backwater, which depends on loss of momentum within the jam. To guide catchment-scale representation, best-fit increased channel resistance was found to increase with number of jams, approaching an analytically determined maximum for close inter-jam spacing, useful for setting an upper envelope for efficacy.

A comprehensive model of plastic wear based on the discrete element method

A comprehensive computational model of wear has been developed. It simulates the wearing of a surface due to both scratching with a rigid indenter or normal/oblique impact of a rigid projectile. A group of spheres models the surface, characterised by the hardness. When the pressure overcomes a threshold, spheres are displaced to account for the change in surface profile. In the case of impact, the wear volume grows with the velocity and reaches a maximum between 0 and 90 ∘ . In the case of scratching, the dependence of the worn volume on the normal load is linear in a limited range of loads (Archard’s law) and transitions to a non-linear behaviour with the increase of load. Energy dissipation is naturally included in the model without additional parameters. This conceptually simple approach can easily be extended to model a variety of industrial applications and potentially predict wear patterns under varying scenarios. • A unified wear model has been developed for both impact and scratching scenarios. • An abradable surface is discretised using small spheres in DEM. • The change in surface profile due to wear is captured by displacing the spheres. • Simulations show a qualitative agreement with literature data.

Integrated analysis of exoskeletal surface profile and chitin-related gene expression on Macrophthalmus japonicus mud crabs exposed to hexabromocyclododecane

Hexabromocyclododecanes (HBCDs), widely used brominated flame retardants, easily accumulate in aquatic organisms such as Macrophthalmus japonicus crabs, which inhabit tidal flat sediments. To analyze the effects of HBCD exposure in chitin-formed exoskeleton, we investigated molecular responses of chitin-related genes as well as physical changes of the exoskeletal surface form as a new biological end-point on M. japonicus. The expression patterns of chitin biosynthesis-, modification-, and degradation-related genes in the gills and hepatopancreases of M. japonicus were also analyzed. Additionally, the survivability and exoskeleton surface profiles of M. japonicus crabs were evaluated. M. japonicus chitin synthase expression was significantly downregulated, whereas that of the chitinase transcript was significantly upregulated upon exposure to all HBCD concentrations on day 7. Contrastingly, the gene expression of chitin deacetylase 1 significantly increased upon exposure to all HBCD concentrations on day 1, and this increase was significantly elevated on day 4. The expression of chitin deacetylase 1 was dose-dependent. Additionally, decreased survival and exoskeleton surface profile changes were observed in M. japonicus crabs exposed to all HBCD concentrations. These results suggest that exposure to HBCD induces changes in the synthesis, modification, and degradation of chitin, a pivotal component of the cuticular exoskeleton, and may disrupt the exoskeletal surface structure in M. japonicus crabs.

Vibration-based monitoring and prediction of surface profile change and pitting density in a spur gear wear process

Gear wear often results in both tooth profile changes caused by abrasive wear, and fatigue pitting. Being able to accurately monitor and predict the profile change (i.e., the wear depth in the direction normal to the gear surface) and surface pitting propagation can bring enormous benefits to industrial practice. However, there is a lack of efficient, reliable, and effective tools to do so. To address this, this paper proposes a gear wear monitoring and prediction approach through the integration of: (i) a dynamic model, to simulate the dynamic responses of the gear system; (ii) two tribological models, to estimate wear depth (in the direction normal to the gear surface) and pitting density (on the gear surface); and (iii), model updating, by comparing simulated and measured vibration signals.More specifically, a 21-degree-of-freedom dynamic model is used to simulate a spur gearbox setup and produce simulated vibrations and contact forces between the meshing gear teeth. Using the contact pressure (calculated from the force) as an input, the wear depth and pitting density are then predicted by the tribological models and used to modify the gear geometry profile and contact area in the dynamic model. The developed approach allows the dynamic model and the wear models to communicate so that both the gear tooth profile change and pitting density can be simulated continuously. To guarantee accurate prediction results from the models, novel approaches are developed to update the wear coefficients in the tribological models by comparing simulated and measured vibrations. The paper demonstrates the ability and effectiveness of the proposed vibration-based methodology in monitoring and predicting gear wear, specifically the tooth profile change and surface pitting propagation, using measurements from both a lubricated test, dominated by surface pitting propagation with mild tooth profile change, and a dry test dominated by tooth profile change.

Image stitching for fringe projection profilometry

There are many optical methods for extracting the geometric information of an object from an image. The structured light method based on digital fringe projection is widely employed. Sometimes the fringe patterns have some undesired invalid areas due to drastic surface profile changes of the tested object, or geometric discontinuities. In addition, a large projection angle affects the quality of the acquired data. These invalid areas may introduce difficulties for further processing. We propose to combine image fusion methods and a typical structured light system to alleviate the shadow problems created by a single projector.

Enhanced Corrosion Resistance of a Double Ceramic Composite Coating Deposited by a Novel Method on Magnesium-Lithium Alloy (LA43M) Substrates

In this study, a composite coating with outstanding corrosion and wear resistance was successfully produced on LA43M substrates. The composite coating was composed of cold-sprayed aluminum, anodized Al2O3 and a SiO2 sealing coating, which was defined as the MAC composite coating. The properties of the MAC composite coating were characterized by water contact angle, potentiodynamic polarization, salt spray corrosion test, electrochemical impedance spectroscopy and ball-on-disk test, while the microstructure was investigated by scanning electron microscope. The wear results show that the double ceramic composite coating improves the wear resistance compared to the LA43M substrate. After sealing with polysilazane, the surface of the MAC composite coating became hydrophobic. Thus, the corrosion current density dropped to 5.4 × 10−9 A cm−2, which is by four orders of magnitude lower compared to that of the LA43M alloy. Furthermore, there was no significant change in surface roughness and profile after long-term corrosion test, demonstrating the outstanding corrosion resistance of the MAC composite coating. In addition, the MAC composite coatings presented the highest impedance loop, impedance moduli and the phase angles, hence confirming that the MAC composite coatings provided a high degree of corrosion resistance for LA43M alloy.

Adding Terrain Height to Improve Model Learning for Path Tracking on Uneven Terrain by a Four Wheel Robot

Closely tracking a defined path by a wheeled mobile robot on a three-dimensional surface is important for accurate movement on uneven terrain. Conventional methods in two dimensions are difficult to extend to three dimensions due to the computational complexity in finding wheel-terrain interactions. Learning based methods bypass the need for explicit modelling and can accurately predict these dynamic relations. We use learning based Model Predictive Controller (MPC) for path tracking by a four-wheel robot. A neural network is used as a model due to its capability for learning complex state transition dynamics. Learning terrain height information aids the MPC on uneven terrain. The algorithm is rigorously tested in simulation on a variety of terrain profiles to track paths by a four wheel robot's center of mass. Results show the method is robust to model errors and that our novel method of incorporating terrain height information significantly improves performance on terrains with high frequency surface profile changes.

Finite Element Study of the Effect of Internal Cracks on Surface Profile Change due to Low Loading of Turbine Blade

Turbine blades for thermal power plants are exposed to severe environments, making it necessary to ensure safety against damage, such as crack formation. A previous method detected internal cracks by applying a small load to a target member. Changes in the surface properties of the material were detected before and after the load using a digital holographic microscope and a digital height correlation method. In this study, this technique was applied in combination with finite element analysis using a 2D and 3D model simulating the turbine blades. Analysis clarified that the change in the surface properties under a small load varied according to the presence or absence of a crack, and elucidated the strain distribution that caused the difference in the change. In addition, analyses of the 2D model considering the material anisotropy and thermal barrier coating were conducted. The difference in the change in the surface properties and strain distribution according to the presence or absence of cracks was elucidated. The difference in the change in the top surface height distribution of the materials with and without a crack was directly proportional to the crack length. As the value was large with respect to the vertical resolution of 0.2 nm of the digital holographic microscope, the change could be detected by the microscope.

Study and modeling of propellant ablation in coaxial ablative pulsed plasma thrusters

The influence of the main design parameters on the ablated mass bit (the mass ablated from the propellant in each discharge) of a coaxial ablative pulsed plasma thruster is analyzed in this paper. The analysis results show that the main influencing factor of the ablated mass bit in coaxial ablative pulsed plasma thrusters is the ablation energy from the arc. When the ablation energy is given, the shape and size of the propellant surface mainly affect the distribution of the ablated mass but have less influence on the ablated mass bit. Based on the analysis, a simple model that can be used to estimate the ablated mass bit of the coaxial ablative pulsed plasma thruster is established. To evaluate and complete the new model, a coaxial ablative pulsed plasma thruster is operated and tested under 10 different working conditions. The experimental results show that the ratio of the ablated mass bit to the absolute value integrals of the product of the electrode voltage and discharge current is approximately 0.38–0.49 μg/J. When the ratio is set to 0.44 μg/J, the maximum and average errors of the new model are 15.7% and 7.6%, respectively, for ablated mass bits under these 10 working conditions. The concept of the ablation direction is proposed in this paper. The experimental and simulation results show that the ablation direction has a great influence on the propellant surface profile change in coaxial ablative pulsed plasma thrusters, which also affects their performance and reliability.

Metrological changes in surface profile, chip, and temperature on end milling of M2HSS die steel

The effect of the thermal energy generated during end milling on the surface profile and chip morphology with a change in the spindle speed and feed rate is studied and reported. Steels with 5% molybdenum have found an amicable application as molybdenum based high speed die steel (M2HSS). It is used as the machining material. Taguchy's L9 orthogonal array machining condition is performed for two different tool diameters of 10 mm and 12 mm. High machining temperatures initiate a local welding zone, creates a weldment between the chip and tool surface, and progress to excess tool wear. This experimental study reveals that the details of increased thermal interaction that allows an excessive deformation of the sample through chip removal. With an increase in the high level of spindle speed and low feed rate, it is possible to get an acceptable level of surface profile roughness with a less tool wear rate. Further, the chip morphological analysis was performed and reported.

Metrological changes in surface profile, chip, and temperature on end milling of M2HSS die steel

The effect of the thermal energy generated during end milling on the surface profile and chip morphology with a change in the spindle speed and feed rate is studied and reported. Steels with 5% molybdenum have found an amicable application as molybdenum based high speed die steel (M2HSS). It is used as the machining material. Taguchy's L9 orthogonal array machining condition is performed for two different tool diameters of 10 mm and 12 mm. High machining temperatures initiate a local welding zone, creates a weldment between the chip and tool surface, and progress to excess tool wear. This experimental study reveals that the details of increased thermal interaction that allows an excessive deformation of the sample through chip removal. With an increase in the high level of spindle speed and low feed rate, it is possible to get an acceptable level of surface profile roughness with a less tool wear rate. Further, the chip morphological analysis was performed and reported.

Ultrasound-assisted 3D printing of continuous fiber-reinforced thermoplastic (FRTP) composites

Investigation of manufacturing continuous fiber reinforced thermoplastic polymer composites (CFRTPCs) through 3D printing technologies has attracted great attention in the past few years due to excellent properties of CFRTPCs, such as high strength-to-weight ratio and stiffness. It is found that the properties of CFRTPCs are affected not only by the properties of the individual parent materials but also by interfacial characteristics. Modification of the interface is a great method to improve the wettability between fiber and polymer and hence the mechanical properties of CFRTPCs. In this work, an ultrasound-assisted 3D printing device for CFRTPCs is developed. The changes of surface profile and chemical structure of carbon fiber and carbon fiber prepreg after ultrasonic treatment are studied. The effects of ultrasonic processing parameters on the microstructure and mechanical properties of CFRTPCs are provided. It is found that the tensile and flexural strength of composite materials are improved by 34% and 29%, respectively, compared with untreated material by using the ultrasonic amplitude of 40 μm, resin solution mass fraction of 10%, processing speed of 15 mm/s.

Study on the Wear Characteristics of a Lapping Wheel in Double-Sided Lapping Based on the Trajectory Distribution

In the process of double-sided lapping, the surface shape of the lapping wheel changes because of uneven wear, which affects the quality of the workpiece, especially the surface shape accuracy of the workpiece (bow, warp, and total thickness variance). Lapping trajectory is the primary reason for uneven wear on the wheel surface. Therefore, the uniformity of the lapping wheel wear during the double-sided lapping process will be investigated based on the trajectory distribution in this paper. First, the kinematics of double-sided lapping is analyzed, and the lapping trajectory equation is established. Then, the simulation calculation is conducted using MATLAB software to obtain the trajectory distribution characteristics of the wheel surface. The wear uniformity of the wheel surface is analyzed according to the distribution density of the trajectory. The wear model of the lapping wheel surface is established. Finally, double-sided lapping experiments with sapphire slices are carried out. Under varied workpiece material removal thicknesses, the changes of the lapping wheel surface profile are measured, and the wear of the lapping wheel surface along the radial direction is obtained and compared with the calculation results. The calculation results are basically consistent with the experimental results, which proves the correctness of the double-sided lapping wheel surface wear model.