Groove Roughness Research Articles

Study on the influence of surface roughness on the diffraction efficiency of two-dimensional gratings.

This study investigates the effect of surface roughness on the diffraction efficiency of two-dimensional gratings. Firstly, a roughness model was constructed using FDTD, followed by a significant analysis of the ridge roughness, groove roughness, and sidewall roughness on diffraction efficiency. Then, the impact of each roughness type on diffraction efficiency was studied separately. Results indicate that ridge roughness has a negative impact on diffraction efficiency, whereas groove roughness and sidewall roughness have a positive impact on the diffraction efficiency of two-dimensional gratings. When ridge, groove, and sidewall roughness coexist, diffraction efficiency decreases with an increase in roughness, consistent with previous research. However, under conditions of minimal roughness, diffraction efficiency actually increases. Finally, an experiment was conducted to verify the conclusions. The results of this study have significant reference value for the application and development of precision measurement techniques for gratings.

Oriented fibrous poly (butylene adipate-co-terephthalate) matrices with nanotopographic features: Production and characterization

This is the first study to systematically investigate the effectiveness of electrospinning parameters and solvent properties on the random and aligned poly (butylene adipate-co-terephthalate) (PBAT) fiber surface nanotopography. Therefore, the combinations of three groups of solvents, good solvents, and a non-solvent, were used. While THF (tetrahydrofuran), HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) and DCM (dichloromethane) were selected as good solvents, DMSO (dimethylsulfoxide) was chosen as a non-solvent. Four different phase separation mechanisms, non-solvent-induced phase separation (NIPS), vapor-induced phase separation (VIPS), breath figure (BF), and thermally induced phase separation (TIPS) mechanisms, were applied to create roughness on the fiber surfaces. Smooth, porous and groove surfaces with average fiber diameters in the range of about 800–2000 nm were obtained at different electrospinning conditions by these phase separation mechanisms. Porous random fibers with a few small pores were obtained by NIPS in the presence of THF/DMSO, while corrugated random fibers were produced by VIPS with DCM/HFIP. The groove roughness on the aligned THF/DMSO and aligned DCM/HFIP fibers was achieved by the TIPS mechanism thanks to the rapid evaporation rate of THF and HFIP. The most porous fibers were obtained in the presence of moisture with a good solvent mixture of DCM/HFIP. The results of this investigation show that the use of good and non-solvents together with moisture control affected not only the topography of fibrous matrices but also the bulk characteristics of PBAT nanofibrous matrices.

Influence of Groove Roughness on Crack Initiation of PEEK Thrust Bearing in Water

In order to research the relation between fracture and texture conditions of PEEK thrust bearing in water, the rolling contact fatigue, RCF test was carried out. And then, the specimen after test was observed with a laser confocal microscope. Three types of surface damage: single crack, flaking and multiple crack: were ob-served. Arithmetic Average Roughness Height, AARH’s around single crack and no-damaged area were calculated. AARH’s in these two areas have no sig-nificantly different each other. This means the effect of cracks on roughness was negligible, and vice versa. The changing of AARH during the test was also dis-cussed. AARH’s both of failure and non-failure specimens were decreased dur-ing RCF tests. AARH Range of non-failure specimens after test included that of the failure specimen. It indicated AARH was not dominated the condition failure of PEEK bearing in water. On the other hands, the load had a clear threshold. This means the failure of PEEK bearing in water is strongly affected by load.

Experimental and numerical investigation of flow structure of grooved cylinder

Making modifications to a cylinder is one of the most effective ways to change the flow in the cylinder wake region. This study aimed to investigate experimentally and numerically the flow structure of the wake region of a smooth cylinder and rectangular grooved cylinders (roughness coefficients are ϵ/D = 0.02, 0.04, and 0.06, ϵ is the roughness height, and D is the diameter of the cylinder) by using the Particle Image Velocimetry (PIV) and the Computational Fluid Dynamics (CFD). Numerical studies were conducted with the Reynolds-averaged Navier-Stokes (RANS) equations. The experimental studies were performed at Re = 5000 in an open water channel, while the numerical studies were performed at Reynolds numbers in the range of 5000 ≤ Re ≤ 20000. A good agreement was observed between the experimental and the numerical results in terms of the time-averaged patterns, time-averaged velocity profiles, and Strouhal numbers. The saddle points of the rectangular grooved cylinders were closer to the surface compared to those of the smooth cylinder. The results revealed that the time-averaged drag coefficient reduced by 30% for the largest groove roughness (ε/D = 0.06) at Re = 20000. In conclusion, the present study shows that rectangular grooved cylinders are effective in reducing the time-averaged drag coefficient.

Дифракционные решетки с блеском, получаемые на пластинах Si --- первые результаты

Using direct laser lithography and liquid etching of polished vicinal Si(111) wafers, a technology was developed and diffraction gratings 500 /mm with a blaze angle of 4° were fabricated. The manufacturing process of a reflective Si-grating of a triangular profile (sawtooth) can be divided into four main steps: (1) obtaining a pattern of a protective mask for etching grooves; (2) anisotropic etching of grooves in KOH solution; (3) etching to smooth the grating profile and polish the surface of working facets; (4) coating to increase reflectivity. The samples obtained were characterized using scanning electron microscopy and atomic force microscopy methods to determine the shape of the groove profile and roughness: the shape turned out to be close to the ideal triangular, and the root-mean square roughness was less than 0.3 nm. With the help of the PCGrate™ code, taking into account the measured real groove profile, the diffraction efficiency of gratings operating in classical and conical mounts in soft-X-ray and extreme ultraviolet radiation has been simulated. The obtained efficiency values are close to the record ones for the corresponding spectral range and the Au-coating of the grating.

Erosion Mechanism of a Cavitating Jet on Groove Roughness

The erosion behavior of a cavitating jet on groove roughness was investigated experimentally using mass-loss characteristics, scanning electron microscopy (SEM) observation, time-resolved shadowgraph, and schlieren flow visualizations. The wall morphology of the cavitating-jet erosion on the groove roughness indicated an increased mass loss, which was highly increased along the groove rather than across the groove. Furthermore, increased erosion pits were observed on the groove bottom along the grooves. The shadowgraph imaging of the cavitating jet on the rough wall showed noncircular cavitation bubble distributions along and across the grooves, which corresponds to the increased number of cavitation bubbles along the grooves and the decreased number of bubbles across the grooves. This result is consistent with the erosion morphology of the groove roughness. Schlieren imaging indicated that the frequency and intensity fluctuation of the shockwave formation did not change significantly on the groove roughness along and across the grooves. The findings in the study show that the increased erosion mechanism on groove roughness is caused by the increased number of impulsive forces and the shockwave focusing effect on the groove bottom.

Liquid droplet impingement erosion on multiple grooves

This short communication is based on a previous experimental study of liquid droplet impingement (LDI) erosion of groove roughness published in Wear 432–433 (2019). In the present study, further experiments were performed using a spray-jet apparatus to understand the erosion mechanism of triple and quadruple grooves using a scanning electron microscope. It was found that the erosion behavior of triple grooves is similar to that of double grooves, as reported in the previous article. However, the erosion behavior of the quadruple grooves is different from that of the double grooves owing to the presence of less eroded groove peaks far from the surrounding smooth walls. This is due to the weakened side-jet effect from the surrounding smooth walls on the isolated groove peak erosion. Furthermore, the role of the central smooth wall between two single grooves was studied, and a decreased erosion was observed with an increase in the length of the smooth wall. These experimental results explain the importance of the surrounding smooth walls on the erosion behavior of grooves.

Influence of surface roughness on liquid droplet impingement erosion

In this paper, liquid droplet impingement (LDI) erosion on the groove roughness of aluminum (A1070) is studied both experimentally and numerically, to understand the erosion mechanism on rough surfaces. The experiments are carried out using spray–jet erosion apparatus. The erosion rates on two kinds of roughness (W and V grooves) are measured, and the erosion patterns are observed using a scanning electron microscope (SEM). An early erosion is observed on the W groove in comparison with the V groove, which is caused by removal of the groove peak. The SEM observations show that the erosion initiates from the groove trough of the W groove and intrudes into the lower side of the groove peak, which is followed by the removal of the groove peak. Furthermore, numerical simulation is carried out for a single droplet impingement on the W groove to explain the physical mechanism of early erosion from the point of impact pressure distribution on the grooves. It is found that the shock wave loading at the groove peak generates high impact pressure on the peak, while the focused shock wave generated by droplet impact on the groove trough and middle generates a similar magnitude of pressure impact on the trough. This corresponds to continual pressure impacts on the groove trough, and results in an increased erosion rate on the W groove roughness.

Liquid droplet impingement erosion on groove roughness

A study of erosion mechanism during the liquid droplet impingement (LDI) on a rough surface was conducted using both numerical simulation and experiments. The numerical simulation was carried out for the LDI on single groove roughness utilizing the two-phase full Eulerian approach based on the high-resolution finite volume method to understand the evolution of the droplet deformation and the wall pressure distribution. The numerical results for the LDI on a large groove roughness showed that the first and the second impacts occurred close to the first contact location of the droplet on the wall, which was similar to the LDI on a smooth surface. The largest impact occurred by the third impact at the groove bottom, which was caused by the side-jet focusing and droplet focusing generated from the contact edge of the droplet. It was also found that the maximum wall pressure at the groove bottom increased with the increase in the groove roughness parameter that represented the geometrical ratio of the groove depth to the droplet diameter. In addition to the numerical studies, the erosion behavior of LDI on single groove roughness was observed experimentally using a Scanning Electron Microscope (SEM) after spray jet impingement on an aluminum specimen with various groove roughness parameter. The experimental results showed that the LDI erosion on the large groove roughness started from the groove bottom, while the LDI erosion on the small groove roughness started from the groove edge and the groove bottom. These experimental findings are well correlated with the maximum wall pressure distributions obtained from the numerical results.

Experiments on liquid droplet impingement erosion on a rough surface

Liquid droplet impingement (LDI) erosion on a rough surface was studied experimentally in the initial stage of erosion using spray-jet impingement on various levels of sandpaper roughness and single groove roughness. The experimental results using an aluminum specimen indicated that the incubation period decreased and the erosion rate increased with increasing the relative roughness, defined as the ratio of roughness height to droplet diameter, in a range of small relative roughness. The growth of the erosion rate in a large relative roughness is almost constant for the sandpaper roughness with increasing the relative roughness, while the erosion rate for the groove roughness decreased at large relative roughness. Therefore, the erosion rate of the groove roughness indicated a peak at small relative roughness. This might be due to the influence of smooth surface surrounding the single groove roughness. A scanning electron microscope (SEM) observation for the small relative roughness of groove showed that erosion was started on the sidewall of the grooves and was followed by the penetration of erosion perpendicular to the groove. The erosion initiation points shifted from the sidewall to the bottom of the groove with increasing the relative roughness, which might be due to the effective impact angle variation across the groove.

Heat transfer and fluid flow characteristics in air duct with various V-pattern rib roughness on the heated plate: A comparative study

This article presents three dimensional CFD (computational fluid dynamics) investigation of local Nusselt number and local friction factor ratios in an air channel with various V-pattern ribs as roughness elements employed on one wall. The various ribs such as, V-pattern rib, protrusion rib in V-pattern, dimpled rib in V-pattern, and V-pattern rib combined with groove have been considered in the study. The CFD analysis on heat transfer and fluid flow characteristics is conducted to investigate the overall effects of the various V-pattern rib shapes on the thermal hydraulic performance. The results found that V-pattern rib with a combination of groove roughness shapes provides better thermal hydraulic performance than other comparable V-pattern rib roughness shapes.

Heat transfer and fluid flow analysis of artificially roughened ducts having rib and groove roughness

Artificially roughness is one of the well known methods of enhancing heat transfer from the heat transfer surface in the form of repeated ribs, grooves or combination of ribs and groove (compound turbulators). The artificial roughness produced on the heat transferring surface is used in cooling of gas turbine blades, nuclear reactor, solar air heating systems etc. Solar air heaters have wide applications in low to moderate temperature range, namely, drying of foods, agricultural crops, seasoning of wood and space heating etc. Solar air heaters have low value of convective heat transfer coefficient between the working fluid (air) and the heat transferring surface, due to the formation of thin laminar viscous sub-layer on its surface. The heat transfer from the surface can be increased by breaking this laminar viscous sub layer. Hence, in the present work compound turbulators in the form of integral wedge shaped ribs with grooves are used on the heat transfer surface, to study its effect on the heat transfer coefficient (Nusselt number) and friction factor in the range of Reynolds number 3,000–18,000. The roughness produced on the absorber plate forms the wetted side of upper broad wall of the rectangular duct of solar air heater. The relative groove position (g/p) was varied from 0.4 to 0.8 and the wedge angle (Φ) was varied from 10° to 25°, relative roughness pitch (p/e) and relative roughness height (e/D) was maintained as 8.0 and 0.033 respectively. The aspect ratio of the rectangular duct was maintained as 8. The Nusselt number and friction factor of the artificially roughened ducts were determined experimentally and the corresponding values were compared with that of smooth surface duct. It is observed that wedge-groove roughened surface shows more enhancement in heat transfer compared to only rib roughened surface arrangement. The investigation revealed that Nusselt number increases 1.5–3 times, while the friction factor increases two to three folds that of the smooth surface duct in the range of operating parameters. It is also observed that in rib–groove roughness arrangement with relative groove position of 0.65 shows the maximum enhancement in the heat transfer compared to the other rib-groove roughness arrangements. Statistical correlations for the Nusselt number and friction factor have been developed by the regression method in terms of the operating and roughness parameters. A program was also developed in MATLAB for the calculation of thermal efficiency and thermal effectiveness. It was observed that the thermal efficiency is more for wedge angle of 15° and relative groove position of 0.65 and its value ranges from 42 to 73 %. The uncertainties in the measurements due to various instruments for the Reynolds number, Nusselt number, and friction factor have been estimated as ±3.8, ±4.54 and ±7.6 % respectively in the range of investigation made.

Fabrication of Micro Ni-W Electroplated Diamond Tools and Their Application to Grooving of Brittle Materials

The present paper intends to improve the tool quality and the machining performance of micro cylindrical Ni-W electroplated diamond tools. From the grooving tests of silicon the following results were obtained. The scatter of diamond grit density on the tool surface can be prevented through the intermittent pouring of electroplating solution into the solution with grit supported by a filter. Ni strike plating before electroplating is useful for extending the tool life, but it can result in the degradation of roughness on groove side surface. Tool wear may result from the removal of bond material due to generated chip and dropped diamond grit, therefore the usage of harder bond material and the heat treatment of bond material are recommended. For a constant tool diameter there exists a suitable grit diameter from the viewpoint of machining efficiency and groove roughness. In grooving of quartz glass, chippings of 10-20μm may occur on the groove edges, which can be prevented by the application of axial ultrasonic vibration to the tool.

Second law optimization of a solar air heater having chamfered rib–groove roughness on absorber plate

Artificially roughened solar air heaters perform better than the plane ones under the same operating conditions. However, artificial roughness leads to even more fluid pressure thereby increasing the pumping power. The entropy generation in the duct of solar air heater having repeated transverse chamfered rib–groove roughness on one broad wall is studied numerically. Roughness parameters, viz., relative roughness pitch P/ e, relative roughness height e/ D h relative groove position g/ P, chamfer angle φ and flow Reynolds number Re have a combined effect on the heat transfer as well as fluid friction. The entropy generation is minimized and reasonably optimized designs of roughness are found.

Focused ion beam-shaped microtools for ultra-precision machining of cylindrical components

Focused ion beam (FIB) sputtering is used to shape a variety of cutting tools with dimensions in the 15–100 μm range and cutting edge radii of curvature of 40 nm. The shape of each microtool is controlled to a pre-specified geometry that includes rake and relief features. We demonstrate tools having rectangular, triangular, and other complex-shaped face designs. A double-triangle tip on one tool is unique and demonstrates the versatility of the fabrication process. The FIB technique allows observation of the tool during fabrication, and, thus, reproducible features are generated with sub-micron precision. Tools are made from tungsten carbide, high-speed tool steel, and single crystal diamond. Application of FIB-shaped tools in ultra-precision microgrooving tests shows that the cross-section of a machined groove is an excellent replication of the microtool face. Microgrooves on 40–150 μm pitch are cut into 3 mm diameter polymer rods, for groove arc lengths greater than 12 cm. The surface finish of machined features is also reported; groove roughness ( R a) is typically less than 0.2 μm. Ultra-precision machining of cylindrical substrates is extended to make bound metal microcoils having feature sizes of 20–40 μm.