Values Of Roughness Parameters Research Articles

Sustainable Diamond Burnishing of Chromium–Nickel Austenitic Stainless Steels: Effects on Surface Integrity and Fatigue Limit

This study aims to evaluate the influence of lubrication and cooling conditions in the diamond burnishing (DB) process on the surface integrity and fatigue limit of chromium–nickel austenitic stainless steels (CNASSs) and, on this basis, identify a cost-effective and sustainable DB process. Evidence was presented that DB of CNASS performed without lubricating cooling liquid satisfies the requirements for a sustainable process: the three key sustainability dimensions (environmental, economic, and social) are satisfied, and the cost/quality ratio is favorable. DB was implemented with the same values of the main governing factors; however, four different lubrication and cooling conditions were applied: (1) flood lubrication (process F); (2) dry without cooling (process D); (3) dry with air cooling at a temperature of −19 °C (process A); and (4) dry with nitrogen cooling at a temperature of −31 °C (process N). Conditions A and N were realized via a device based on the principle of vortex tubes. All four DB processes provide mirror-finished surfaces with Ra roughness parameter values from 0.041 to 0.049 μm, zones with residual compressive stresses deeper than 0.5 mm, and increases in the specimens’ fatigue limit (as determined by the accelerated Locati’s method) compared to turning and polishing. Processes F and D produce the highest microhardness on the surface and at depth. The process D introduces maximum compressive residual axial and hoop stresses in the surface layer. The dry DB processes (D, A, and N) form a submicrocrystalline structure with high atomic density, which is most strongly developed under process D. When high fatigue strength is required, DB with air cooling should be chosen, as it provides a more favorable cost/quality ratio, whereas dry DB without cooling is the most suitable choice for applications that require increased wear resistance.

EFFECT OF BUILD POSITION ON SURFACE ROUGHNESS OF SLM PRINTED INCONEL 718

The present work investigates the variation of the surface roughness due to the build position of specimens with respect to the inert gas flow direction and re-coater movement direction. Selective laser melting (SLM) method was used to study this effect using Inconel 718 as workpiece material. A total of 21 samples were placed equidistant from each other on the built plate to observe the effect of gas flow and re-coater movement. The effect of these parameters on the printed samples was analyzed in terms of the profile surface roughness parameter such as Ra and Rz in the build direction. The result showed that samples placed near the gas inlet and the re-coater starting position had larger roughness as compared to the samples placed further from the gas inlet and re-coater end position. The result showed that the profile average roughness parameter values varied from Ra = 5.02 µm to 14.7 µm and profile maximum height surface parameter varied from Rz = 47.61 µm to 118.3 µm for all the printed samples. Surface topography of the samples was also studied which showed common printing defects such as cracks, micropores, local solidified melt pools, and dimples. The study opens an avenue to explore and optimize the placement of the printing sample on the build plate with respect to the inlet gas flow and re-coater movement directions for better surface roughness.

Optimization and evaluation of thermo-hydraulic performance of solar air heaters equipped with different roughness geometries

Solar air heaters have poor thermal efficiency. Applying artificial roughness elements is a common approach to enhance thermal performance of a solar air heater. In this study, fluid flow and heat transfer characteristics of solar air heaters equipped with six different roughness geometries, including inline cubical elements, staggered cubical elements, rectangular baffles, square ribs, V-shaped baffles, and V-shaped ribs, were assessed. First, parameters of each roughness geometry were optimized and then thermo-hydraulic performance of solar air heaters having optimum roughness geometries was compared. For each roughness geometry, two design parameters were selected and 25 numerical experiments were designed based on the full factorial design of experiment approach. The thermo-hydraulic performance parameter (THPP) was set out as the objective function and its relationship with roughness parameters was defined using the non-parametric regression response surface method. Finally, the optimum values of roughness parameters were determined using the nonlinear programming by quadratic Lagrangian (NPQL) technique. Comparing the performance of solar air heaters having optimum roughness geometries showed that rectangular baffles led to the largest and inline cubical elements brought about the smallest THPP at almost all Reynolds numbers. The maximum THPP of rectangular baffles was 2.28 at the Reynolds number of 25,000.

Insight into antibacterial effect of titanium nanotubular surfaces with focus on Staphylococcus aureus and Pseudomonas aeruginosa

Materials used for orthopedic implants should not only have physical properties close to those of bones, durability and biocompatibility, but should also exhibit a sufficient degree of antibacterial functionality. Due to its excellent properties, titanium is still a widely used material for production of orthopedic implants, but the unmodified material exhibits poor antibacterial activity. In this work, the physicochemical characteristics, such as chemical composition, crystallinity, wettability, roughness, and release of Ti ions of the titanium surface modified with nanotubular layers were analyzed and its antibacterial activity against two biofilm-forming bacterial strains responsible for prosthetic joint infection (Staphylococcus aureus and Pseudomonas aeruginosa) was investigated. Electrochemical anodization (anodic oxidation) was used to prepare two types of nanotubular arrays with nanotubes differing in dimensions (with diameters of 73 and 118 nm and lengths of 572 and 343 nm, respectively). These two surface types showed similar chemistry, crystallinity, and surface energy. The surface with smaller nanotube diameter (TNT-73) but larger values of roughness parameters was more effective against S. aureus. For P. aeruginosa the sample with a larger nanotube diameter (TNT-118) had better antibacterial effect with proven cell lysis. Antibacterial properties of titanium nanotubular surfaces with potential in implantology, which in our previous work demonstrated a positive effect on the behavior of human gingival fibroblasts, were investigated in terms of surface parameters. The interplay between nanotube diameter and roughness appeared critical for the bacterial fate on nanotubular surfaces. The relationship of nanotube diameter, values of roughness parameters, and other surface properties to bacterial behavior is discussed in detail. The study is believed to shed more light on how nanotubular surface parameters and their interplay affect antibacterial activity.

Medium-Scale Soil Moisture Retrievals Using an ELBARA L-Band Radiometer Using Time-Dependent Parameters for Wetland-Meadow-Cropland Site

The soil moisture at the medium spatial scale is strongly desired in the context of satellite remote sensing data validation. The use of a ground-installed passive L-band radiometer ELBARA at the Bubnów-Sęków test site in the east of Poland gave a possibility to provide reference soil moisture data from the area with a radius of 100 m. In addition, the test site comprised three different land cover types that could be investigated continuously with one day resolution. The studies were focused on the evaluation of the ω-τ model coefficients for three types of land cover, including meadow, wetland, and cropland, to allow for the assessment of the soil moisture retrievals at a medium scale. Consequently, a set of reference time-dependent coefficients of effective scattering albedo, optical depth, and constant-in-time roughness parameters were estimated. The mean annual values of the effective scattering albedo including two polarisations were 0.45, 0.26, 0.14, and 0.54 for the meadow with lower organic matter, the meadow with higher organic matter, the wetland, and the cropland, respectively. The values of optical depth were in the range from 0.30 to 0.80 for the cropland, from 0.40 to 0.52 for the meadows (including the two investigated meadows), and from 0.60 to 0.70 for the wetland. Time-constant values of roughness parameters at the level of 0.45 were obtained.

Discrimination of wear performance based on surface roughness parameters arithmetic mean height (Sa) and skewness (Ssk)

Enhancing interfacial contact bearing performance typically involves minimizing the roughness parameter Sa (arithmetic mean height). Yet, exceedingly low Sa incur steep increases in processing costs, indicating that Sa-centric optimization strategies may not be universally suitable for interface performance control. Roughness parameters skewness (Ssk) and kurtosis (Sku) exert a pronounced influence on component contact wear performance. Accordingly, investigating the correlation between Ssk, Sku, and wear performance holds significant promise for enhancing wear resistance. A finite element wear calculation model for rough-surface abrasive wear employing elastic-plastic contact mechanics and the Jump-in-Cycle method. Cylindrical roller dry sliding experiments validate the model's reliability. Integrating this model, a method is proposed for wear performance discrimination based on Sa and Ssk at different loads. It enables the identification of critical roughness parameter values for improved surface wear resistance. The calculated wear model aligns with experiment trends, with predicted surface textures mirroring observed wear surface characteristics. Critical Sa and Ssk diverge under distinct loads. The study underscores the importance of moving beyond the exclusive pursuit of exceptionally low Sa and Ssk. It provides a foundation for reducing workpiece processing costs while optimizing wear performance.

Effect of Macro Fibers on the Permeability and Crack Surface Topography of Layered Fiber Reinforced Concrete.

This paper describes the effects of macro fibers on permeability and crack surface topography of layered fiber-reinforced concrete (FRC) specimens with different layering ratios under uniaxial tensile load. The crack permeability of layered FRC specimens is investigated by a self-designed permeability setup. The topographical analysis of crack surfaces is investigated by a custom-designed laser scanning setup. The results show that when the fiber volume content and layering ratio of the FRC layer are constant, the tensile toughness of layered FRC specimens depends on the proportion of steel fiber in macro fibers, and with an increase in the proportion of steel fiber, the tensile toughness of layered FRC specimens increases. For the layered FRC specimens, the crack permeability is much lower than that of the normal concrete (NC) specimen. A significant positive synergistic effect on crack impermeability can be achieved by the combination of steel fiber and polypropylene fiber in the SF80PP2.3 specimen. The crack surface roughness parameter (Rn) values of the NC layer in layered FRC specimens are all higher than those of the NC specimen, and the crack surface Rn of the FRC layer in layered FRC specimens is higher than that of the unlayered FRC specimens. This can effectively increase the head loss of cracks and reduce the crack permeability of layered FRC specimens.

Laser deposited ultra-thin silver nanoparticles on CMC-PVA blend film as sheet for wound dressings

In this study, silver nanoparticles (AgNPs) were synthesized using pulsed laser deposition and deposited on a sheet film composed of Carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and AgNPs. These polymeric-based nano-composites were investigated for their potential application in wound healing. The structural properties of the composites were examined using X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). Morphological features were observed through field emission scanning electron microscopy (FESEM), and roughness characteristics were studied using FESEM micrographs. The CMC-PVA-AgNPs scaffolds with deposition times of 10 and 12.5 min showed minimal deviations in surface structure compared to the composites with longer deposition times, where scattered AgNPs and aggregates were observed. Furthermore, the roughness parameter (Ra) values indicated the potential of silver NPs in creating trapping sites and crystal defects, as evidenced by an increase in Ra from 18.96 nm in the pure CMC-PVA blend to 34.17 nm at a deposition time of 20 min. The optical properties of the composites were investigated by determining the band-gap of direct and indirect transition modes, which exhibited a decreasing trend. The presence of silver NPs was confirmed by the plasmon absorption band observed around 400 nm. The intensity of the plasmon peaks increased with longer laser deposition times, indicating an increase in the silver content over time. Finally, the antibacterial activity of the prepared scaffolds against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Micrococcusluteus was evaluated, and the results strongly support the potential of the prepared material for biological applications. In conclusion, the synthesized CMC-PVA-AgNPs nano-composites deposited using pulsed laser deposition technique exhibited promising properties for wound healing applications. The comprehensive characterization of the composites, including their structural, morphological, optical, and antibacterial properties, provides valuable insights for further research and development in the field of biomaterials.

The effect of recycled fibers on shear properties of concrete at different ages and damage constitutive model based on 3-dimensional morphology analysis

To study the shear properties and damage constitutive model of plain concrete (PC) and nylon fiber recycled from waste reinforced concrete (RNFRC), the direct shear test under different normal stresses (σn, from 1 to 5 MPa) with a continuous horizontal rate of 0.5 mm/min is conducted on the cube specimens at different ages. The 3D roughness parameters of shear surface and the evolution of shear strength components are studied. Results show that the peak shear strength of RNFRC at 3, 7 and 28 d ranges from 6.65 to 12.09, 8.07–13.94 and 8.93–15.27 MPa under different σn, exhibiting varying degrees of enhancement compared to those of PC. The values of the 3D roughness parameter C gradually increase while Rs and the joint roughness coefficient (JRC) decrease with increasing σn. The evolution of shear strength components is affected clearly by σn. The calculation results of shear damage constitutive model match well with the experimental results.

Rough Surface Aerodynamic Computation in Rarefied Gas Flow Applying the Solution of Inverse Problem

Most effective method to find the roughness parameters in rarefied gas flow is to calculate them from aerodynamic measurements, solving the inverse problem. The value of the main roughness parameter obtained from the solution of inverse problem is substantially higher (at least 1,25–1,5 times) than similar value of the same parameter measured from the profile diagrams. Thus, the effect of surface roughness in aerodynamic values of rough surface in rarefied gas flow is always significantly underestimated. First main reason of it is the low precision of roughness parameter measurements from the profile diagrams, and the second is based on usual lack of taking into account aerodynamic shadowing effect.

Thermal and effective assessment of solar thermal air collector with roughened absorber surface: an analytical examination

Abstract The current work analyses the thermal (ηth) and effective efficiency (${\eta}_{\mathrm{eff}}$) of a solar thermal air collector (STAC) that has an arc-shaped dimple as a roughness geometry on the absorber plate. Nusselt number (Nu) and friction factor (ff) were computed for roughness geometry during the testing, which was done on STAC. Additionally, for different roughness values, the correlations for Nu and ff were developed and further used in this study. The temperature rise parameter and a parametric design are used to assess these efficiencies. The influence of design variables on STAC performance is analyzed using a numerical model based on thermal and effective evaluations. During the investigation, parameters such as relative roughness height (e/Dh) varied from 0.021 to 0.036, relative roughness pitch (p/e) from 10 to 20, arc angle (α) from 45 to 60°, temperature rise parameter from 0.003 to 0.02 and Reynolds number (Re) from 3000 to 48 000 at a constant solar intensity (I = 1000 W/m2). The ηth and ${\eta}_{\mathrm{eff}}$ are observed to be 85% and 78%, respectively, at the optimum values of roughness parameters, i.e. e/Dh = 0.036, p/e = 10, and α = 60°. The curves have been plotted between each of the roughness parameters and Re in order to evaluate the best ηth and ${\eta}_{\mathrm{eff}}$ . The research emphasizes the usefulness of MATLAB for STAC analysis and optimization, roughness parameters of the suggested collector design, by integrating simulation and experimental data.

Hydraulic Bottom Friction and Aerodynamic Roughness Coefficients for Mangroves in Southwest Florida, USA

Mangroves are a natural feature that enhance the resilience of natural and built coastal environments worldwide. They mitigate the impacts of hurricanes by dissipating energy from storm surges and waves, as well as reducing wind speeds. To incorporate mangroves into storm surge simulations, surface roughness parameters that accurately capture mangrove effects are required. These effects are typically parameterized using Manning’s n bottom friction coefficient for overland flow and aerodynamic roughness length (z0) for wind speed reduction. This paper presents the suggested values for these surface roughness parameters based on field observation and a novel voxel-based processing method for laser scanning point clouds. The recommended Manning’s n and z0 values for mangroves in southwest Florida are 0.138 and 2.34 m, respectively. The data were also used to retrain a previously developed random forest model to predict these surface roughness parameters based on point cloud statistics. The addition of the mangrove sites to the training data produced mixed results, improving the predictions of z0 while weakening the predictions of Manning’s n. The paper concludes that machine learning models developed to predict environmental attributes using small datasets with predictor features containing subjective estimates are sensitive to the uncertainty in the field observations.

Eco-friendly ink formulation of column purified carbon dots from GABA for anticounterfeiting applications

Forgery of valuable products causes a negative impact on the society as well as the economy of the country. There is a growing demand to not only differentiate or authenticate genuine documents/products but also to protect their integrity. Carbon dots (CDs) are a class of fluorescent nanomaterials that are well-known for their facile synthesis, good photostability and less toxicity profile. The current research work focuses on the preparation of CDs via hydrothermal method using γ-aminobutyric acid (GABA) that contains amino and carboxylic groups. Column chromatography technique is adopted to purify the GABA-derived CDs from the reactants and by-products. The fourth fraction obtained after column purification containing CDs with fluorescence emission in the visible region is chosen for further studies. The presence of spherical CDs confirmed through TEM imaging are chemically characterised using SAED, EDS, DLS, FTIR, XPS, Raman and XRD spectroscopy. The blue (λem = 490 nm) and green (λem = 538 nm) emitting CDs present in the fourth fraction displayed a fluorescence lifetime of 1.90 ns and 2.02 ns. Theoretical studies are performed using B3LYP/6-31G(d,p) theory level on different plausible structures. The HOMO-LUMO band gap of 2.3 eV deduced using DFT calculation is in close agreement with the optical band gap of 2.6 eV derived from Tauc plot. A complex forming mechanism is proposed for the fluorescence quenching of CDs upon examining the EDS data of the precipitate obtained upon addition of cupric ions. Further, the CDs are used as pigments to formulate a water-based ink for flexographic printing on UV-dull paper substrate. The printed samples exhibited good colorimetric values, lightfastness, and rub resistance. The security features of the ink film include an UV-induced yellow fluorescence, which will be known to the forger and a secondary quenching of fluorescence when exposed to cupric ions, which can be used by the user to validate document/product authenticity. This stimulus responsive optical property is also explored in the design of ionochromic security paper based on cupric ion induced fluorescence quenching of CDs for data storage and decryption. Moreover, the lesser surface roughness and electrical parameter values obtained for the print proofs could be further explored for the potential application of CD-derived ink in electronic anticounterfeiting.

Accuracy of tracking radio altimeters working over a 2D rough surface

Low altitude tracking radio altimeters use periodic frequency modulated continuous signals and the altitude measurement is based on estimation of the mean frequency of the beat signal. To realize the estimation, a closed automatic control loop is organized in radio altimeter. The loop maintains the frequency of the beat signal at a fixed value by adjusting some parameters of the transmitted signal. There is one more way to build up a tracking contour for the altitude estimate, the operation of which is based on the use of a measuring phase locked loop. The circuit adjusts the reference signal ‑ a copy of the beat signal ‑ to maximize the phase structure of the beat signal and the reference signal. When measuring the height over a rough surface, in addition to errors caused by the internal noise in the receiver, the range noise begins to affect the accuracy of the estimate. The range noise is due to the formation of a signal scattered by a rough surface as sum of reflections from stationary points of the surface where the local normal is directed towards the phase center of the radio altimeter antenna. The article aim is a comparative analysis of the accuracy of three types of tracking radio altimeters working over a rough two-dimensional surface: radio altimeter with a phase-locked loop and tracking altimeters with adjustment of the frequency deviation or the modulation period of the transmitted signal. The signal reflected from a two-dimensional rough surface was simulated by the method of stationary points, which is a particular case of the Kirchhoff method. As a result of the simulation, the biases and the root-mean-square errors of height estimates were obtained for the three types of tracking altimeters and different values of the surface roughness parameter. For all altimeters, the estimate bias is small and does not depend on the roughness parameter. The root-mean-square error of height estimation for all considered radio altimeters increases with increase of the roughness parameter. The best results were shown by the radio altimeter with the measuring phase locked loop. Its error is approximately 3 times less than that of the radio altimeters with adjustment of the transmitted signal parameters.

ROUNDNESS ERROR AND TOPOGRAPHY OF HARD TURNED SURFACES

Accuracy and topography are significant indicators of precision machined high-quality surfaces. Case hardened steel (16MnCr5) was analyzed to obtain information about the effects of technological data and the connections between the analyzed accuracy (roundness) and roughness parameters (Sa, Sz, Ssk, Sku). It was found that the feed rate has a significant influence on the roundness and the roughness parameters, and there are strong relationships between the roundness and these roughness parameter values: the correlation coefficients varied between 0.78 and 0.85.

Analysis of Vibration, Deflection Angle and Surface Roughness in Water-Jet Cutting of AZ91D Magnesium Alloy and Simulation of Selected Surface Roughness Parameters Using ANN.

The use of magnesium alloys in various industries and commerce is increasing due to their properties such as high strength and casting properties, high vibration damping capability, good shielding of electromagnetic radiation and high machinability. Conventional machining methods can, however, pose a risk of ignition. AWJM is a safe alternative to conventional machining, but the deflection and vibration of the water jet can affect surface quality. Therefore, the aim of this study was to investigate the effects of selected AWJM parameters on the surface quality and vibration of machined magnesium alloys. Jet deflection angle, surface roughness parameters and vibration during AWJM were investigated. The findings showed that higher skewness occurred at a lower abrasive flow rate, while higher average values of the Sku roughness parameter were obtained at ma = 8 g/s in the range of 60-140 mm/min. It was also observed that higher vibration values occurred at ma = 8 g/s. The input parameters for creating an artificial neural network (ANN) model used in this study were the cutting speed vf and the mass flow rate ma. The results of this study provided valuable insights into ways of ensuring a safe and efficient machining environment for magnesium alloys. The use of ANN modeling for predicting the vibration and surface roughness of AZ91D magnesium alloy after water-jet cutting could be an effective tool for optimizing AWJM parameters.

Effects of surface roughness and counter body variables on the dry sliding wear behavior of AISI 4140 steel based on the elastoplastic flattening model

This study aimed to determine the effect of surface roughness and counter body material on the wear behavior of AISI 4140 steel based on the elastoplastic flattening model. Most studies in tribology based on the elastoplastic regime focus on modeling the contact between a sphere and a flat surface. However, these models’ main challenge is determining the real contact area. This study claims that the real contact area can be detected with high accuracy through interface software used in optical microscopy. The sample surfaces were roughened and then supposed to dry sliding wear tests using the AISI 52100 and Al2O3 abrasive counter bodies under varying loads and test durations. It was concluded from the calculations that the sample’s surface roughness value significantly affects the contact pair’s plasticity index and, thus, the sample’s wear behavior against the counter body material. Higher plasticity index values indicating the abrasive effect were obtained with the Al2O3 ball, which has a higher hardness and elasticity modulus than the AISI 52100 steel ball. The surface damage of the sample with a high roughness value was less than the other samples. The COF values obtained with the steel ball were detected as lower than that of the alumina ball. Also, it was seen that the surface roughness parameter and plasticity index values calculated were compatible with the wear characteristics of the test samples. As a result, determining the real contact area between the contacting surfaces and its usability in calculating the elastoplastic flattening model parameters were experimentally tested and verified.

Mechanical properties of CAD/CAM polylactic acid as a material for interim restoration

Statement of problemBiomaterials, including polymethyl methacrylate (PMMA) and bisacrylate, have been widely used as conventional interim materials and may exhibit cytotoxicity or systemic toxicity. PurposeThis study was designed to compare the mechanical properties of polylactic acid (PLA) as an alternative to conventional dental polymers for computer-aided design and manufacturing (CAD/CAM). Material and methodsFour groups (n = 20 per group) of CAD/CAM polymers were assessed. Specimens of PLA (PLA Mill) and PMMA (PMMA Mill) for subtractive manufacturing, PLA for fused deposition modeling (PLA FDM), and bisphenol for additive manufacturing by stereolithography (Bisphenol SLA) were fabricated into 2-mm-wide, 2-mm-thick and 25-mm-long specimens using a milling machine, an FDM printer, and an SLA printer, respectively.The flexural strength (FS) and elastic modulus (EM) were calculated. The surface roughness and Shore D hardness were analyzed with a 3D optical surface roughness analyzer and a Shore durometer, respectively. ResultsPLA Mill showed the lowest FS (64.9 ± 8.28), followed by PLA FDM (104.27 ± 4.42 MPa), PMMA Mill (139.2 ± 20.95 MPa), and Bisphenol SLA (171.56 ± 15.38 MPa), with statistically significant differences. PLA FDM showed the highest EM, followed by PLA Mill, Bisphenol SLA, and PMMA Mill. Significant differences were observed not only between PMMA Mill and Bisphenol SLA but also between PLA FDM and PLA Mill. The lowest Shore D hardness was observed for PLA FDM, followed by PLA Mill, PMMA Mill, and Bisphenol SLA, which showed the highest value among the 4 groups, with significance. The highest values for the surface roughness parameters were observed for PLA Mill, and the lowest were observed for Bisphenol SLA. ConclusionsAmong the tested CAD/CAM polymers, Bisphenol SLA was the most durable material, and the mechanical properties of PLA FDM were within the clinically acceptable range.

Моделирование взаимосвязей между входными факторами и выходными показателями процесса внутреннего шлифования с учетом взаимных колебаний инструмента и заготовки

Introduction. In real production conditions, the technological modes recommended in the scientific literature do not reflect the declared qualities, due to the fact that it does not take into account many factors inherent in the process of finishing grinding, for example, its stochastic nature, changes in its dynamic properties, an increase in mutual vibrations of the tool and the workpiece that appear due to changes in the state of the technological system, for example, an increase in vibrations machine tool due to uneven tool wear, etc. All previously developed models have a limited scope of application, it does not take into account the fact that the appearance of vibrations leads to fluctuations in the depth of grinding, with accidental contact of grains with the material being processed, where one group of grains cuts off the material, the other gets into the trace of scratches left by previous grains, etc. This leads to changes in the values of material removal, surface roughness and other parameters of the technological system, which directly affects the accuracy of processing and the quality of the machined surfaces. The purpose of the work is to develop mathematical models that establish the relationship between the processing modes and the current parameters of the contact zone during the fine grinding of pinholes, taking into account the mutual vibrations of the tool and the workpiece. The research methods are mathematical simulation using the basic provisions of the theory of abrasive-diamond processing. Results and discussion. The interrelations between the cutting modes and the current input parameters of the contact zone when grinding pinholes are established, taking into account the mutual vibrations of the tool and the workpiece, which make it possible to determine the parameters of the system at the output to avoid cost losses, including reducing the number of defective products and time costs. Non-stationary mathematical dependences are constructed that allow determining the cutting modes during the implementation of the grinding cycle, taking into account the magnitude of relative vibrations and the initial phase. It is established that instead of a steady process, harmonic oscillations are observed caused by deviations in the shape of the circle, the intensity of tool wear and other factors, all of the above has a significant impact on the quality of the machined surface. The obtained models are universal for various characteristics of the tool, however, for a more adequate description of the process, mathematical dependencies are needed that take into account the wear of the tool on various binders, which is the task of further research.

Toothpaste Abrasion and Abrasive Particle Content: Correlating High-Resolution Profilometric Analysis with Relative Dentin Abrasivity (RDA).

In this in vitro study, the influence of the concentration of abrasive particles on the abrasivity of toothpastes was investigated using laser scan profilometry on polymethyl methacrylate (PMMA) surfaces with the aim of providing an alternative method to developers for screening of new toothpaste formulations. PMMA plates were tested in a toothbrush simulator with distilled water and four model toothpastes with increasing content of hydrated silica (2.5, 5.0, 7.5, 10.0 wt%). The viscosity of the model toothpaste formulations was kept constant by means of varying the content of sodium carboxymethyl cellulose and water. The brushed surfaces were evaluated using laser scan profilometry at micrometer-scale resolutions, and the total volume of the introduced scratches was calculated along with the roughness parameters Ra, Rz and Rv. RDA measurements commissioned for the same toothpaste formulations were used to analyze the correlation between results obtained with the different methods. The same experimental procedure was applied to five commercially available toothpastes, and the results were evaluated against our model system. In addition, we characterize abrasive hydrated silica and discuss their effects on PMMA-sample surfaces. The results show that the abrasiveness of a model toothpaste increases with the weight percentage of hydrated silica. Increasing roughness parameter and volume loss values show good correlation with the likewise increasing corresponding RDA values for all model toothpastes, as well as commercial toothpastes without ingredients that can damage the used substrate PMMA. From our results, we deduce an abrasion classification that corresponds to the RDA classification established for marketed toothpastes.