Dimple Depth Research Articles

The Influence of Surface Patterning on the Thermal Properties of Textured Thrust Bearings

Contact performance can be enhanced by using textured surfaces. These are also found to have influences on lubricated contacts. A procedure to find the optimal partially textured thrust bearing configuration is presented in this study. A parallel sector-pad thrust bearing is simulated by a three-dimensional (3D) computational fluid dynamics (CFD) model. The stationary surface of the bearing is textured with dimples, while the rotor surface is flat. The results of the baseline model are validated by experimental data. In this study, we compare rectangular and elliptical dimples by investigating design parameters, such as major the length of the major axis (width), the length of the minor axis (length), dimple depth, circumferential space between two dimples, radial space between two dimples, radial extent, circumferential extent are selected as design parameters. A parametric study is conducted to investigate the influence of the texture geometries and a surrogate model is created. Based on the surrogate model, a multi-objective optimization scheme is used to navigate the design space and find the optimal texture structure that provides a lower maximal temperature inside the fluid film, higher load capacity, and lower friction torque. The results show that the optimal radial extent of the texture is around 80% of the pad radial length for both cases. The optimal length of the elliptical dimples in the circumferential direction is about 30% larger than the value of the rectangular dimples. In the final optimal design, the maximal temperature reduces 1.1% and 1.3% for rectangular and elliptical dimples while the load capacities are maintained at the same level.

Influence of dimple and spot-texturing of HSS cutting tool on machining of Ti-6Al-4V

Machining of titanium alloys using high speed steel (HSS) tools is difficult due to their lower thermal conductivity which increases temperature of the HSS cutting tools thus accelerating their wear. Texturing on rake face of a cutting tool has recently emerged as a promising and environment friendly method enhancing removal of heat from the machining zone. This paper reports study on influence of spot and dimple textures by micro-plasma transferred arc powder deposition (μ-PTAPD) process on rake face of the HSS cutting tools. Experiments were conducted to study effects of μ-plasma power, powder flow rate and exposure time on dilution of spot-textures by making spots of Stellite powder on the HSS tool and to identify their optimum values for making an array of spots on rake face of the HSS tool. Similarly, effects of μ-plasma power and exposure time on diameter, depth, and aspect ratio of dimples were studied to identify their optimum values for producing an array of dimples on rake face of the HSS tool. Spot-textured, dimple-textured, and non-textured HSS tools were used in turning of Ti-6Al-4 V alloy and their performance was compared in terms of machining forces, flank wear, tool temperature, chip shapes, and surface roughness of the turned workpiece. Use of spot-textured HSS tool resulted in least values of cutting and thrust forces, chip-tool contact length, tool temperature, flank wear, adhesion of the workpiece material to the tool, and average surface roughness of the turned workpiece than the dimple-textured and non-textured HSS tools at different cutting speeds. Performance of the dimple-textured HSS tool was better than the non-textured tool in these aspects. Spots helped in formation of segmented chips by reducing curling radius of chips whereas non-textured and dimple-textured tools formed continuously curling ribbon-like chips. Spots also act as fins which enhance heat loss to the machining environment and helping in reduction of tool temperature. This study proves that spot-texturing of rake face of HSS tool by μ-PTAPD process is an economical, effective and environment friendly method to improve machining of titanium alloys.

Numerical Simulation and Experimental Analysis of Grease Friction Properties on Textured Surface

This research article is a numerical simulation study and experimental verification of the frictional behaviors of grease lubricated sliding contact under mixed lubrication conditions. The influences of surface texture parameters on the frictional properties were investigated. A numerical simulation model was specifically developed in MatLab which employs the average flow Reynolds equation established on the basis of finite-element analysis to compute the friction coefficient, pressure distribution, and film thickness. The results showed that friction coefficient is largely dependent on texture parameters with higher and lower dimple depths resulting in higher friction coefficient at a fixed dimple density. The sample with texture density of $$T_{\text{d}} = 15\%$$ and texture depth of $$H_{3} = 7$$ μm exhibited the best friction properties experimentally, because it can store more grease and trap wear debris. Through the comparison of the simulated results of the current model with the ring-on-disc experimental results, the validity of the mixed lubrication model was confirmed. However, the lowest friction coefficient occurs at dimple depth of 5 μm and texture density of 10% which is slightly at variance with the experimental results. The simulated results exhibit the reduction of friction for surface texturing and the main mechanism for such an effect may be attributed to the hydrodynamic pressure effect of the surface texturing, which increases the mating gap and reduces probability of asperity contact.

Microstructure, mechanical properties and post-weld heat treatments of dissimilar laser-welded Ti2AlNb/Ti60 sheet

Dissimilar joining of Ti2AlNb and Ti60 rolled sheet was performed by laser beam welding. The microstructures and mechanical properties of as-welded and post-weld heat-treated Ti2AlNb/Ti60 joints were investigated by microstructure observation and mechanical properties testing. The fusion zone (FZ) of the as-welded joint consisted of B2/β matrix and small S2 balls. The heat-affected zones HAZ-Ti2AlNb and HAZ-Ti60 for the as-welded joint were characterized as α2 + B2/β + O and α′ + α + β + S2, respectively. The tensile strength and elongation of as-welded sheet were 597.5 MPa and 6.2% at 650 °C, respectively. Most of the plastic deformation was taken place at the side of Ti60 alloy. With the increase in the heat treatment temperature, the anchoring strength between each other of B2/β grains was enhanced by the precipitated lamellar α′ and O grains at the FZ. The depth of the fracture dimples increased with the heat treat temperature increasing. The heat-treated welding joint at 970 °C presented a good balance of the tensile strength and plasticity, where the tensile strength and the elongation were enhanced to 669.7 MPa and 7.1% at 650 °C, respectively.

A numerical study on heat transfer enhancement and flow structure in enhanced tube with cross ellipsoidal dimples

Flow characteristics and heat transfer performance of enhanced tube with cross ellipsoidal dimples are numerically analysed in this research work. The special arrangement is a conventional plain tube with longitudinal and transverse dimples at each cross-plane. The objective is to present details of flow field structure and heat transfer mechanisms for the dimpled tube. Additionally, effects of dimples depth, pitch and axis ratio on thermal–hydraulic performance also being discussed. The realizable k-ε turbulence model was employed in the numerical simulations with the Re range from 5000 to 30,000. The velocity contour, temperature contour, local streamlines, velocity vectors and Nu were presented to illustrated the heat transfer enhancement mechanisms. From this investigation, it is found that the transverse and longitudinal dimples cause downward flow, improve the flow mixing and reattachment, interrupt the boundary layer and form periodic impingement flows and then greatly improve the heat transfer. Nu of TCED increase with the increase of depth and axis ratio, and decrease with increase of pitch. Under operating condition and geometric parameters considered, the TCED with D = 2 mm, P = 20 mm, R = 2.2 and Re = 5000 obtained the largest PEC value about 1.58.

Investigation on Performance of Mechanical Seal with Varying Dimple Depth Along the Radial Face

Investigation on Performance of Mechanical Seal with Varying Dimple Depth Along the Radial Face

Comparative study on the influence of depth, number and arrangement of dimples on the flow and heat transfer characteristics at turbulent flow regimes

The ensuing study is dedicated to a series of numerical investigations concerning the effects of various geometric parameters of dimpled plates on the flow structure and heat transfer performance in a rectangular duct compared to the smooth plate. These parameters are the arrangement, number and depth of dimples. Two widely used staggered and square patterns in addition to a triangular arrangement, and three dimple depths (Δ = δ/d = 0.25, 0.375 and 0.5) have been chosen for this particular study. All studies have been conducted at three different Reynolds numbers Re = 25,000, 50,000 and 100,000. In order to capture the flow structures in the vicinity of dimples and contributing phenomena related to the boundary layer interactions, fully structured grids with y+ < 1 have been generated for all the cases. The realizable kt-e two-layer model was selected as a proper turbulent model. It can be observed from the obtained results that higher effective area for heat transfer and a myriad of turbulent vortices mixing the hot fluid near the surface with the passing cold fluid generated from the downwind rims of dimples are the causes for improved average Nusselt number in the dimpled surface in comparison to the smooth plate. However, more pressure loss due to the higher friction drag and recirculation zones inside dimples will exist as a drawback in this system. Moreover, for all arrangements increasing dimple ratio Δ has a negative impact on the heat transfer augmentation and also deteriorates the pressure loss, which leads to this fact that Δ = 0.25 serves as the best option for the dimple depth.

The Effects of Microdimple Texture on the Friction and Thermal Behavior of a Point Contact

This study investigates the effects of the microdimple texture on the friction and surface temperature performances of a ball-on-disk contact, operating under the speed and load ranges that cover typical gearing applications. Circular-shaped microdimple arrays with different dimple center distances and dimple depths are implemented on the ball surface to quantify the impacts of these two parameters on the friction coefficient and the maximum ball surface temperature. In addition, the contacts of three surface texture combinations, namely microdimpled and polished ball surface versus polished disk surface, polished ball surface versus polished disk surface, and ground ball surface versus ground disk surface, are compared to demonstrate any beneficial or detrimental effect of microdimples in heavily loaded high-speed applications. This study adopts a thermal mixed EHL point contact model, whose capability and accuracy have been well demonstrated by comparing to the experimental measurements, to quantify the deterministic tribological behavior within the contact, allowing the exploration of the underlying mechanism that governs the role of microdimples in the elastohydrodynamic lubrication (EHL).

Influence of Donut-Shaped Bump on the Hydrodynamic Lubrication of Textured Parallel Sliders

The influence of donut-shaped bump texture on the hydrodynamic lubrication performance for parallel surfaces is presented in this paper. A mathematical equation has been applied to express the shape of three-dimensional donut-shaped bump texture. Numerical simulation of the pressure distribution of lubricant between a textured slider and a smooth, moving slider has been performed to analyze the geometrical parameters' influence on the hydrodynamic performance for textured surfaces. The numerical results show that the convex of the donut-shaped bump provides a microstep slider, which can form a convergent wedge and build up hydrodynamic pressure. Optimum values of horizontal spacing and bump height are obtained to maximize the hydrodynamic pressure. It is also noted that the average pressure increases monotonically with the increase of bump radius, but decreases with the increase of vertical spacing and dimple depth, respectively.

Numerical and experimental investigation of texture shape and position in the macroscopic contact

Abstract In this work, the influence of operating conditions on the shape parameters of surface texture is investigated by means of both numerical and experimental investigations. The analysed texture consists of micro-dimples obtained through laser surface texturing on a pin-on-disc configuration. From the numerical point of view, particular attention is paid to the faithful representation of the 2D surface of the experimental set-up and to modelling cavitation phenomena through a mass conserving algorithm. As results, the dimple depth shows a higher relevance than diameter in determining the optimal texture shape (both in terms of friction reduction and load carrying capacity). Moreover, the dimple depth, corresponding to the minimal friction, is found to scale with the square root of the Sommerfeld number in agreement with the experimental results. Finally, it is found that a numerical approach with the present hydrodynamic model cannot account for friction reduction obtained experimentally with different orientation of the texture.

Surface Texturing of Polyimide Composite by Micro-Ultrasonic Machining

In this study, micro-dimples were prepared on a polyimide composite surface to obtain the dual benefits of polymer materials and surface texture. Micro-ultrasonic machining is employed for the first time for micro-dimple fabrication on polyimide composite surfaces. Surface textures of simple patterns were fabricated successfully with dimple depths of 150 μm, side lengths of 225-425 μm, and area ratios of 10-30%. The friction coefficient of the micro-dimple surfaces with side lengths of 325 or 425 μm could be increased by up to 100% of that of non-textured surfaces, alongside a significant enhancement of wear resistance. The results show that surface texturing of polyimide composite can be applied successfully to increase the friction coefficient and reduce wear, thereby contributing to a large output torque.

Effect of Equal Channel Angular Pressing on Microstructure and Mechanical Properties of ZL205A Alloy

The evolution of microstructure of ZL205A alloy during equal channel angular pressing (ECAP) by route A at room temperature was investigated by OM, SEM and XRD, and the hardness of cast and heat treatment alloy from different strain were tested. The results showed that the grain of cast alloy were obviously refined, the massive q phase along the grain boundary were crushed, and prompts the distribution of q streamline after one pass through ECAP. After two passes of ECAP, the distribution of q phase is more uniform. After heat treatment through ECAP, the grains were also obviously refined, and elongated in axial direction, which also prompts the distribution of q streamline. The hardness was significantly improved after ECAP. The hardness of cast alloy increases from 65HV to 132HV after two passes, and that of heat treatment alloy increases from 112HV to 198HV. With the increase of extrusion passes, the number of dimples gradually increased and evenly distributed, the depth of dimples was of a similar level, and the distribution of precipitated phase is more uniform.

Influence of Laser Pulse Number on the Ablation of Cemented Tungsten Carbides (WC-CoNi) with Different Grain Size

The ultra-short pulse laser has attracted attention as an advanced tool for functionalizing surface topography, since it has high accuracy and results in little damage. In a previous study, some innovative patterns were introduced on cemented carbide surfaces, such as dimples, which are commonly used as oil reservoirs for bearings. The accuracy is not only related to the inherent features of the laser, but also to the machining processes. Within this context, this study aims to investigate the influence of machining parameters (i.e., pulse number in this study) on the ablation mechanism and resulting surface integrity. Two cemented carbide grades, possessing similar chemical composition but different grain size (small and large), are machined using a femtosond laser set-up with variant pulse number (1–20). The geometrical properties of the produced structure and surface integrity are statistically investigated using different microscopy techniques. It is found that the dimple depth is approximately proportional to the pulse number for both grades, and the coarse grade leads to a higher rate of depth increase. Damage is found in the form of melting and cracking for the binder and the grains, respectively; but this is more pronounced for large-grain grade in terms of the scale and depth. However, these observations are only found at a very superficial position.

Optimization of Ytterbium Laser Parameters for Texturing of Steel Surfaces

Laser surface texturing is used to improve the tribological properties of the sliding surface. Optimizing the laser parameters to get appropriate texture diameter and depth is one of the challenges for tribologist. In the present study, the effect of Ytterbium laser parameters on dimple depth and diameters is investigated. Steel samples with hardness 380HV and Young’s Modulus 200GPa are used. Surface texturing on steel sample surface is done by using an Ytterbium fiber laser system (iPG photonics), with a maximum laser power of 20W, wavelength of 1064nm, maximum frequency of 80 kHz. Input laser parameters (frequency, speed, power, and pulse) are varied to investigate its effect on dimple dimensions and finally optimized. An optical profilometer is used to measure the topography of laser textured samples. Based on the results, it has been found that with an increase in laser power; depth and diameter of dimples are increasing. Contrastingly with an increase in frequency and speed, depth of dimples keeps on decreasing. Variation in pulse length doesn’t show any significant change in dimple dimensions.

Simulation of Dimple Characteristics on the Trajectories of a Dimpled Sphere (Golf Ball) in Motion

A mathematical model describing the flight motion of a golf ball is developed, and the effects of dimple characteristics are studied. Using the Newton’s second law of motion, the equations governing the motion of the golf ball are developed in three dimensions. In this development the size, depth and number of dimples are taken into account. By varying the dimple size, depth and number, the effects of these characteristics are simulated via a MatLab code in which the Dormand-Prince Runge Kutta method is implemented to solve the model equations. The results of the numerical simulations that show how the golf ball trajectory is influenced by the dimple characteristics such as dimple depth, size and number within the accepted range of the Reynolds number are displayed and discussed.

Effect of surface texture parameters on the performance of finite slider bearing

Surface texturing plays an important role to enhance the performance of the tribological components with increase in load carrying capacity and reduction in friction and wear. A numerical study of hydrodynamic lubrication of slider bearing with textured surface is reported. The optimization and comparison of single, double, four, 3600, 2700, 1800, 900 round cylindrical surface cavities are analyzed with incompressible fluid film in isothermal condition. The change in orientation of the surface cavities are studied with different texture parameters like height ratio, area density and dimple depth. The finite volume method is used to solve the Navier-Stokes equation with the help of ANSYS Fluent. It is concluded that 3600 round single cylindrical surface cavity achieves larger pressure and reduction in friction when the cavity is shifted towards the leading side of the bearing as compared to other surface cavities. It is also observed deeper and wider cavity cause a large reduction in the value of coefficient of friction.

Elastic particle deformation in rectangular channel flow as a measure of particle stiffness.

In this study, we experimentally observed and characterized soft elastic particle deformation in confined flow in a microchannel with a rectangular cross-section. Hydrogel microparticles of pNIPAM were produced using two different concentrations of crosslinker. This resulted in particles with two different shear moduli of 13.3 ± 5.5 Pa and 32.5 ± 15.7 Pa and compressive moduli of 66 ± 10 Pa and 79 ± 15 Pa, respectively, as measured by capillary micromechanics. Under flow, the particle shapes transitioned from circular to egg, triangular, arrowhead, and ultimately parachute shaped with increasing shear rate. The shape changes were reversible, and deformed particles relaxed back to circular/spherical in the absence of flow. The thresholds for each shape transition were quantified using a non-dimensional radius of curvature at the tip, particle deformation, circularity, and the depth of the concave dimple at the trailing edge. Several of the observed shapes were distinct from those previously reported in the literature for vesicles and capsules; the elastic particles had a narrower leading tip and a lower circularity. Due to variations in the shear moduli between particles within a batch of particles, each flow rate corresponded to a small but finite range of capillary number (Ca) and resulted in a series of shapes. By arranging the images on a plot of Ca versus circularity, a direct correlation was developed between shape and Ca and thus between particle deformation and shear modulus. As the shape was very sensitive to differences in shear modulus, particle deformation in confined flow may allow for better differentiation of microparticle shear modulus than other methods.

Effect of strain-rate on forming limit in biaxial stretching of aluminum sheet

High-speed biaxial stretching apparatus was developed, where the punch was driven by a drop weight. Effect of the strain-rate on the forming limit strain of thin aluminum A1050 and A5052 sheets was inspected for various strain ratios. Strain-rate was about 100 /s in the high-speed test. It was from 0.0003 to 0.1 /s in the low-speed test. Limit strain of A1050 was larger in high speed. The strain of A5052 in high speed was comparable with that in 0.1 /s, though there exists a slight difference under low-speed conditions. Multiple cracks were formed in high-speed stretching of A5052 attributed to the positive strain-rate sensitivity. Profile of the crack opening is rough in high speed. Growth of the ductile fracture dimple size and depth in microscopic view may play a role to increase the roughness. Sheet thickness at the crack becomes smaller in high-speed stretching, which accords with the tendency of the forming limit strain.

Nd3+:YAG laser surface processing of moly-chrome film at 1064 nm, 532 nm and 355 nm wavelengths

A nanosecond pulsed Nd3+:YAG laser was used to generate grooves as well as dimples on the surface of the moly-chrome film. Interaction of laser, operating at the laser wavelengths of 1064 nm, 532 nm and 355 nm, respectively on the target material were investigated. The principal finding is based on the geometrical parameters such as width, depth and recast layer in the case of the groove. Various roughness parameters inside the grooves were studied. Whereas in the case of the dimple, various parameters like dimple diameter, depth and recast laser were analyzed. A study to find the optical reflectivity of the moly-chrome material at different laser wavelengths was conducted. The groove and dimple formed with the laser wavelength of 1064 nm showed a high material removal and re-cast layer compared to 532 nm and 355 nm. The roughness Ra inside the groove formed with the laser wavelength of 1064 nm and 355 nm exhibited a percentage increase of around 68% and 20% compared to the 532 nm.

Flow and heat transfer characteristics and optimization study on the water-cooled microchannel heat sinks with dimple and pin-fin

In order to develop high-efficiency low-resistance heat exchangers, the heat transfer performance and further optimization of water-cooled microchannel heat sink with dimple and pin-fin were numerically studied in this work. Firstly, the combination effects of structure parameters (diameter of pin-fin D1, depth of dimple δ and stream-wise spacing S) on flow structure and heat transfer were investigated in detail. The results show that the proposed designs exhibit heat transfer augmentation with energy-saving and low-resistance features. The increase of D1 and decrease of S bring out the increase of Nu/Nu0 under all Re studied. Flow structures induced by pin-fin make the development of separation flow in the dimple happened in advance. The increase of D1 enlarges the scale and intensity of wake flow of pin-fin, resulting more violent actions of flow on heated walls, then, enhances the heat transfer augmentation. Also, relative small δ will be beneficial for heat transfer enhancement at lower Re conditions. Furthermore, the automatic calculation configuration optimization analysis by means of pattern search method was validated and conducted successfully to achieve better TP, and the maximum increasement of TP, 10.3%, is obtained at Re = 200 as a result. The area of high temperature regions, especially on the side walls, decreases, also, the temperature gradient decreases and the uniformity of heated walls is enhanced. The proposed method can be extended to optimize configuration of microchannel with flow control devices accurately with less time-consuming.