Initial Roughness Research Articles

Efeito do desafio ácido nas propriedades superficiais das camadas externa e interna de dentes acrílicos reforçados

Resumo Introdução Os dentes acrílicos artificiais devem apresentar característica de resistência aos ácidos, a fim de assegurar a manutenção de suas propriedades, ao longo de sua vida útil. Entretanto, não há estudos disponíveis na literatura pertinente sobre as propriedades superficiais de dureza e rugosidade das diferentes camadas de resina acrílica que compõem os dentes artificiais submetidos a ensaios de erosão simulada. Objetivo Avaliar a dureza e rugosidade superficiais das camadas externa e interna de dentes artificiais acrílicos reforçados submetidos a desafio ácido. Metodologia Molares (SR Postaris e Trilux) seccionados transversalmente foram avaliados inicialmente quanto à dureza Vickers e rugosidade. Esses ensaios foram repetidos após metade das amostras de cada tipo de dente (n=10) ser imersa em água destilada (controle) e outra metade em vinagre durante 15 min/dia por 28 dias. Os resultados foram analisados por ANOVA 2-critérios e teste de Tukey (α=0,05). Resultado A dureza inicial da camada externa dos dois diferentes tipos de dente não sofreu alteração significativa pelo desafio ácido (p>0,05) e a imersão em vinagre não causou efeito deletério à dureza inicial da camada interna dos dois tipos de dentes avaliados (p>0,05). Após 28 dias, a rugosidade inicial de ambos os tipos de dentes estudados, para as duas camadas, não foi alterada com água ou vinagre (p>0,05). Conclusão Os dentes acrílicos reforçados foram resistentes ao desafio ácido uma vez que suas camadas interna e externa não apresentaram alteração significativa de dureza e rugosidade superficiais.

The evolution of hardness and tribofilm growth during running-in of case carburized steel under boundary lubrication

Abstract Many newly manufactured components are subject to a run-in procedure. The objective of this study was to understand how the surface hardness of 16MnCr5 bearing steel evolved during running-in and how varying contact pressure and initial composite roughness affected this evolution. The evolution of the tribofilm formed by zinc dialkyl dithiophosphate (ZDDP) and how it contributed to the measured hardness was also analyzed. The results indicated a higher initial composite roughness led to greater gains in hardness as compared to higher contact pressure during the running-in process. Tribofilm growth appeared to have little to no significant effect on the measured surface hardness increase during running-in and the primary contributor to the observed hardness increase was work hardening.

Effects of substrate surface roughness and nano/micro particle additive size on friction and wear in lubricated sliding

Macroscopic wear experiments were complemented by atomistic simulations to study the effect of nano- and micro-scale titanium dioxide particle lubricant additives on friction and wear. The size of the particles and initial roughness of the sliding surfaces were varied to characterize the interrelated effects of these two properties. Results from both experiments and simulations suggest that there is an optimal particle size that will minimize friction and wear for a given surface roughness. Analyses support a previously-proposed mechanism for particle-based additives in which the particles fill in valleys on the sliding surfaces. In this context, particles that are smaller than the characteristic roughness of the surfaces are most likely to perform this function.

Influence of Nickel Catalyst Morphology on Layer‐Exchange‐Based Carbon Crystallisation of Ni/a‐C Bilayers

Metal-induced crystallisation with layer exchange is applied on Ni/C bilayer stacks deposited by three PVD techniques on SiO2. The layer stacks were deposited at room temperature by either ion beam sputtering, direct current magnetron sputtering or high-power impulse magnetron sputtering. The influence of the Ni morphology on the layer exchange degree αLE and the resulting graphitic ordering is studied by atomic force microscopy, Rutherford backscattering spectrometry and Raman spectroscopy. The initial RMS roughness of the Ni top layer varied with the deposition technique by a factor of 20, from 0.3 to 6.1 nm. After annealing in UHV at up to 700 °C, layer exchange was observed for all samples. Still, the layer exchange degree was affected by the roughness of the initial bilayer stack. The highest value of 96% was achieved for magnetron-sputtered samples, what is by ∼35% higher than for the initially roughest Ni surfaces. Raman spectroscopy showed the formation of graphitic carbon, characterised by a strong 2D line, for all three bilayer stacks. The degree of graphitic ordering increased with decreasing Ni surface roughness.

Development of prediction models of running-in attractor

Abstract Running-in attractor is a stable and time-space ordered structure formed in running-in process. To establish prediction models of the running-in attractor, orthogonal experiments were performed by sliding pins against a disc during the running-in process. The attractors were reconstructed from the measured friction force signals. Their characteristic parameters were computed, and forming time was identified from phase trajectory plot. The variance analysis of characteristic parameters of running-in attractors was conducted to identify the primary and secondary factors for characteristic parameters. The models were established based on response surface method. The running-in attractor can be predicted by the models as long as the working conditions and the initial surfaces roughness are given, which provides reference to running-in design.

Role of nanoparticles generation in the formation of femtosecond laser-induced periodic surface structures on silicon.

An initial roughness is assumed in the most accepted Sipe-Drude model to analyze laser-induced periodic surface structures (LIPSS). However, the direct experimental observation for the crucial parameters is still lacking. The generation of nanoparticles and low-spatial frequency LIPSS (LSFL) (LIPSS with a periodicity close to laser wavelength) on a silicon surface upon a single pulse and subsequent pulses irradiation, respectively, is observed experimentally. Finite-difference time-domain (FDTD) simulation indicates that the nanoparticles generated with the first pulse enhance the local electric field greatly. Based on the experimental extrapolated parameters, FDTD-η maps have been calculated. The results show that the inhomogeneous energy deposition, which leads to the formation of LSFL, is mainly from the modulation of the nanoparticles with a radius of around 100nm.

Antibiofilm properties of model composites containing quaternary ammonium methacrylates after surface texture modification

ObjectiveInvestigate antimicrobial properties and surface texture of model composites with different concentration and alkyl chain length of quaternary ammonium monomers (QAS). MethodsMonomers derived from QAS salts with alkyl chain lengths of 12 carbons ((dimethylaminododecyl methacrylate) DMADDM) and 16 carbons (dimethylaminohexadecyl methacrylate—DMAHDM) were obtained from the reactions of their respective organo-halides with the tertiary amine 2-(dimethylamino)ethyl methacrylate (DMAEMA). DMADDM and DMAHDM were incorporated into model composite in concentrations of 5 or 10%, resulting the following groups: G12.5 (DMADDM 5%), G12.10 (DMADDM 10%), G16.5 (DMAHDM 5%), G16.10 (DMAHDM 10%) and GC (control). Biofilm viability, lactic acid production and surface roughness were analysed 24h after samples preparation (initial), repeated after toothbrush abrasion and after polishing simulation. Data were submitted to ANOVA and Tukey’s test (p≤0.05). ResultsThe longer the molecular chain size of QAS and the higher its concentration (G16.10), the lower was the viability and the production of lactic acid by the biofilm. No differences were detected in initial roughness’ measurements among groups. However, after abrasion, there was an increase of biofilm viability and lactic acid production. Composites containing QAS presented rougher surfaces compared to the CG. After polishing, biofilm viability and surface roughness were statistically similar for all groups. Nevertheless, DMAHDM at 10% showed reduction in lactic acid production. SignificanceChain length and concentration of QAS influenced biofilm development and production of lactic acid. Longer chains and higher concentrations of QAS promoted better antimicrobial properties. Changes in surface texture caused by abrasion, decreased antibiofilm properties.

Technological Parameters Forming the Surface Texture in Hyper Productive Surface Plastic Deformation Processing

The hyper productive surface plastic deformation processing technology called as wide burnishing (WB) was developed in Russian Federation. The mechanics of new WB technology is different from the classic SPD technologies (rolling or burnishing). For example applied force during processing of burnishing is 150-300 N, of WB is 2500-5000 N due to condition of process implementation in mass production with limited processing time (3-4 turnovers of workpiece). WB also has a high degree of deformation due to a multiple deformation passes. To determine the optimal WB processing parameters single and double instrumental devices were implemented and tested. Specimens made of steel 40 and high-strength cast iron 75-50-03 were tested. Initial roughness of steel 40 specimen’s surface was Ra = 0.5 microns and high-strength cast iron was Ra = 0.85 microns. Results of surface texture parameters of processed parts such as surface roughness Ra of steel 40 and high-strength cast iron 75-50-03 under varying load values P and number of cycles (the number of workpieces revolutions during the period of burnishing) were acquired. It was established that the minimum Ra value of the processed surface correspond with values of P = 210 N/mm2 for steel 40 and P = 410 N/mm2 for high-strength cast iron 75-50-03 regardless of number of burnishing cycles. Plastic deformation mechanism (processing time and pressure on the surface) influences on the processed surface roughness formation. It is possible to assume that straining state forms at the optimal values of P in terms of achieving a minimum value of Ra in which the reached degree of hardening allows to minimize the height of the microscopic irregularities of the previous grinding processing. In this case there is no plastic flow of the metal surface layer.

Morphological stability during electrodeposition

Abstract

Maturing of contacts and ageing of silica sand

A typical surface texture of silica sand grains is rich in asperities and mineral debris. Consequently, a nominal inter-granular contact is composed of many ‘contact points’. Associated with the contact loading process is micro-fracturing of the textural features, causing the contact to evolve. Even under a constant load, the process of micro-fracturing continues, although with a decreasing frequency. This static fatigue at contacts (or contact maturing) under a constant load is considered to be a major contributor to ageing of silica sand. The rich surface micro-morphology of silica sand grains is demonstrated using scanning electron microscopy and atomic force microscopy. Grain-scale tests indicate time-dependent deflection under constant load, attributed to delayed fracturing of textural features at grain contacts. The process is greatly dependent on the initial roughness of the surfaces. The rate of the deflection for a grain with large initial roughness (root mean square of grain surface elevation (RMS) = 621 nm), loaded with 2·4 N, was found to be 17·6 nm/h at the end of the first day after loading, whereas for a grain with approximately half the initial roughness (RMS = 321 nm) it was only about 2 nm/h. A consequence of the contact maturing process in grain assemblies is a time-dependent increase in macroscopic stiffness, and a resulting alteration of the stress state in a confined sand. This was confirmed in soft-ring oedometer tests on specimens subjected to constant load. The temporal scale of the radial stress increase in the oedometric samples was about the same as that in convergence tests on single grains. Contact maturing is accelerated by the presence of moisture and pressure dissolution, and this was manifested in tests on samples saturated with pore fluid. The results of both grain-scale and sand specimen tests are consistent with the hypothesis indicating contact maturing as the major contributor to time-dependent effects in silica sand.

The fractal nature of the three-phase boundary: A heuristic approach to the degradation of nanostructured solid oxide fuel cell anodes

Nickel/zirconia-based nanostructured electrodes for solid oxide fuel cells suffer from poor stability even at intermediate temperature. This study quantifies the electrochemical and microstructural degradation of nanostructured electrodes by combining 3D tomography, electrochemical impedance spectroscopy (EIS) and mechanistic modeling. For the first time, the electrochemical degradation of nanostructured electrodes is quantified according to the fractal nature of the three-phase boundary (TPB). Using this hypothesis an excellent match between modeling and the electrochemical response is found. The origin of the degradation in microstructure and electrochemical performance can be found in the initial fractal roughness of the TPB at a length scale not detectable with state-of-the-art tomography at 30nm resolution. This additionally implies that the hydrogen electro-oxidation takes place within 4nm from the geometric TPB line, revealing that the electrochemical reaction zone cannot be regarded anymore as a one-dimensional line when dealing with nanoparticles.

Elastoplastic consolidation solutions for scaling from shallow penetrometers to pipelines

The build-up of friction on seabed pipelines is an important design consideration, affecting their stability and the resulting in-service strain and fatigue. The consolidation beneath a partially embedded pipeline has been investigated in the past and linked to the build-up of axial pipe–soil resistance. This paper extends previous work by providing solutions for consolidation around a new class of shallow penetrometer, to provide a basis to scale from site investigation results directly to the build-up of pipeline friction. Small-strain finite element analyses, using the Modified Cam Clay soil model, are presented for the novel toroid and ball penetrometers. The effects of initial penetrometer embedment, device roughness, strength gradient, and overload ratio have been explored in a comprehensive manner, and are compared with pipe results. The toroid penetrometer shows excellent agreement with an element of an infinitely long pipe, simplifying the scaling process. The ball penetrometer shows a faster consolidation response, typically by a factor of three, reflecting the more effective drainage mechanisms of a three-dimensional device compared to a plane strain device. The dissipation responses are fitted by simple equations to aid application in design.

Atomic layer etching of GaN and AlGaN using directional plasma-enhanced approach

The directional atomic layer etching (ALE) of GaN and AlGaN has been developed. The GaN ALE process consists of cyclic Cl2 plasma chemisorption and Ar ion removal. The etch per cycle (EPC) was 0.4 nm within the self-limiting regime, which is 50 to 100 V. The root-mean-square surface roughness RRMS was 0.6 nm, which was improved from an initial roughness of 0.8 nm. For AlGaN ALE, BCl3 was added to the chlorine step to obtain a smooth surface with RRMS of 0.3 nm and stoichiometry similar to the initial sample. The ultra smooth surface obtained by etching is promising for use in next-generation power devices.

Application of mechanical surface finishing processes for roughness reduction and fatigue improvement of additively manufactured Ti-6Al-4V parts

Currently, additively manufactured (AM) parts have a high initial surface roughness after the manufacturing process, which can be a limitation for application in highly stressed and cyclically loaded areas. In the present study, Ti-6Al-4V samples were manufactured by laser beam melting, annealed and hot isostatically pressed afterwards. They showed an initial surface roughness of Ra=17.9μm depending on their build direction (45°). Subsequently, four different mechanical surface finishing processes were applied separately on plates and fatigue coupons in order to reduce the surface roughness: Milling, blasting, vibratory grinding and a micro machining process. The effectiveness of each treatment is evaluated with respect to the surface topography, as well as the fatigue properties based on axial fatigue tests performed in accordance to DIN EN 6072. The initial roughness could often be reduced to values Ra<1μm. The roughness decrease led to a substantial increase in the fatigue performance from initially 300MPa to a maximum of 775MPa (after 3×107 cycles).

Metallurgical investigations of laser remelted additively manufactured AlSi10Mg parts

AbstractSelective laser melting is gaining importance to manufacture reliable and highly complex parts. However, the surfaces of the selective laser melted parts exhibit for many applications an insufficient high roughness, thus require subsequent post processing steps. A relatively new way to reduce the surface roughness is the laser polishing technique. In the present paper, additively manufactured AlSi10Mg samples were polished with different laser intensities and laser modes. The investigations contain the potential of roughness reduction and enhancement of the surface appearances, which can be achieved by laser polishing of the as‐built surfaces. An initial arithmetic mean roughness of 8.43 μm was remarkably reduced up to 98 %. The compositions of the polished surfaces were detected and the surface appearances were examined. Reasons and mechanisms were explained and depicted for the occurred shade formations on the polished surfaces. High laser intensity led to segregation of silicon and magnesium on the surface. A higher laser intensity enabled an increased melt depth within the conture layer of the selective laser melting structure. Through increasing melt depth, a porosity of max. 1.7 % was detected in the remolten area. Hardness investigations of the initial and laser remolten cross section revealed no significant reduction in hardness.

Concept and Mechanics of Fine Finishing Circular Internal Surfaces Using Deployable Magneto-Elastic Abrasive Tool

Fine finishing of cylindrical internal surfaces without affecting geometric form is a critical requirement in several mechanical and aerospace applications. Although various methodologies using flexible abrasive media are reported for the same, many of them demand complex tooling and fixtures to be developed in tune with the internal dimensions to feed the abrasive media. The present paper investigates the feasibility of using magneto-elastic abrasive balls with the aid of a mechanically deployable tool for microfinishing of geometrically symmetric tubular specimens. The deployable tool used for the present experimentation is designed like an umbrella mechanism, with magnetic pads to hold the elastic abrasive balls, expandable for bore diameter ranges from 45 to 75 mm. The magnetic type elastic abrasive balls proposed in the form of mesoscale balls of diameter 3.5 ± 0.25 mm are capable of finishing the bore surface without altering its roundness. Effects of elastomeric medium, mechanics of material removal and generation of finished profile during the proposed technique have been discussed in detail, through a comprehensive mathematical model. Effect of various process variables on surface roughness was investigated experimentally using response surface methodology and the theoretical predictions were validated at optimum operating condition. Sixty-two percent reduction in average roughness on brass tubes of initial roughness 0.168 μm, with significant improvement in all the associated two-dimensional roughness parameters and without any deviation on roundness, was clearly demonstrating the potential of proposed methodology.

On the process and mechanics of rotary elastoabrasive finishing

ABSTRACTAdvanced finishing processes, both bonded and loose abrasive type, can be used effectively for microfinishing of internal tubular surfaces. However, generation of uniform finish without altering the geometric form is a key challenge in many of the existing methodologies. Rotary elastoabrasive finishing is proposed as a new methodology to meet similar requirements. Elastoabrasives in the form of mesoscale balls are flexible and convenient to use without any slurry/liquid medium and are capable of controlling the abrasion through an elastomeric backup. The mechanics of material removal and the effect of elastomeric medium in the proposed methodology are discussed, supplemented by systematic experimental investigation using response surface methodology. The average roughness of hardened steel tubes with initial roughness 0.160 μm was significantly reduced to 0.017 μm, after a processing time of 40 min without altering their cylindricity. The experimental setup with rotary attachment presented in this paper is demonstrated to be a flexible system for fine finishing tubular specimens, sleeves, and high aspect ratio bores, which find extensive industrial applications.

The temporal variation of farmland soil surface roughness with various initial surface states under natural rainfall conditions

Soil surface roughness not only affects the hydrological and erosive behavior of soils, but also influences their spectral reflectivity in the optical and microwave bands. Field measurement of soil surface roughness is time-consuming, laborious, costly, and, for vegetated areas, impractical. We attempt to find a method to predict the dynamics of soil surface roughness for various soil surface states for black soils in Northeast China. In this study, four soil surfaces with different roughness were designed, and three kinds of roughness parameters, root-mean-square height (rmsh), correlation length (cl) and rmsh/cl, of each soil surface were measured. The results of soil surface roughness were as follows: (1) a decrease over time was observed for rmsh and rmsh/cl as well as an increase in cl over time; (2) an exponential relationship was confirmed between roughness parameters (rmsh, cl, and rmsh/cl) and cumulative rainfall (CR) for soil plots without ridge, as well as for the relative change (RC) of roughness parameters and CR; (3) a significant difference in change of soil surface roughness with CR existed for soil surfaces with ridge and without ridge, and a Gaussian function was more suitable for describing the dependence of soil roughness evolution on CR than an exponential function. These results indicate that the temporal change of soil surface roughness in the black soil of Northeast China could be predicted by CR based on the empirical relationship achieved in this study regardless of whether soil surface has a ridge and of different initial roughness.

The effect of contact pressure and surface texture on running-in behavior of case carburized steel under boundary lubrication

Many engineering tests start with a run-in procedure, as it is commonly accepted that running-in at some fraction of the target load is beneficial due to a reduction in surface roughness. However, the choice of load and duration is often based on historical context or the experience and philosophies of the testing personnel. The objectives of this study were to (1) evaluate the effects of contact pressure and initial composite roughness on the surface evolution during the initial stage of testing, and (2) use this information to determine if there is an optimal load and time for the run-in portion of a test. These tests were conducted with a disc-type machine using carburized steel specimens with a circumferential lay direction and oil with anti-wear additives under specific conditions of slide-to-roll ratio, entraining velocity, oil spin-off temperature, and oil/additive package. The specimen surface was inspected using non-contact profilometery every minute for the first 10minutes of testing, with a subsequently increasing inspection interval for a total of 150minutes. The data demonstrate that the surface roughness reduces within the first few minutes of testing and remains stable for a period of time, which is dependent on the pressure and initial composite roughness. Additionally, hardness measurements indicate that hardness gains are occurring during the test, but over a longer timeframe.

Roles of mirror-like surface finish and DLC coated piston rings on increasing scuffing resistance of cast iron cylinder liners

This study considers two approaches towards increasing the dry scuffing resistance of grey cast iron (CI) cylinder bore (or liner) surfaces, namely by i) decreasing the initial roughness of the CI liner surfaces and ii) by applying a diamond-like carbon (DLC) coating to the top compression piston rings. CI liners were polished to different surface roughness values ranging between 0.08µm and 6.83µm and were subjected to unlubricated reciprocating sliding tests with progressively increasing loads (50–600N) at a constant frequency of 5.0Hz (0.15m/s) using a Cameron-Plint TE77 tribometer. The counterface materials used were CrN coated steel as well as a hydrogenated DLC (H-DLC) coated steel. Microscopic and spectroscopic observations suggested that at low loads a mixed tribolayer comprising of iron oxide (Fe2O3) and graphitic carbon that was formed on wear tracks maintained low wear rates. At higher loads this tribolayer was removed resulting in metallic contact and leading to scuffing. Mirror-polished CI liner contact surfaces (with an average roughness of 0.08µm) provided higher scuffing resistance; the critical scuffing load was 300N compared to 200N for liners with >0.25µm average roughness. The improved scuffing resistance could be attributed to the lower contact stress experienced by the mirror-polished liners with a bearing ratio of 83% compared to medium-finished liners with a bearing ratio of 69%. CrN coated counterface contributed to scuffing of the CI liners at above 300 N load accompanied by a sharp increase in COF (>0.4). The H-DLC coated counterfaces prevented scuffing throughout and maintained a low steady state coefficient of friction (COF) of 0.13 up to 600N load. The low wear of the CI liners run against H-DLC counterfaces was attributed to the formation of the mixed tribolayer on the CI surfaces that remained intact at all tested loads. The results suggest that the use of DLC coated piston rings and a mirror-polish finish of cylinder liners would avert scuffing and provide low COF values while maintaining low wear rates.