Texturing Patterns Research Articles

Enhancement of adhesion strength by micro-rolling-based surface texturing

Structural adhesive bonding technology is widely utilized in various applications in modern automotive and aviation industries. Finding new techniques to enhance adhesion strength between bonded components in a more economical and environmental-friendly way is becoming an important issue. In this paper, a novel micro-surface texturing method by using a developed deformation-based micro-rolling system has been applied to modify surface conditions of a sheet metal in order to increase metal-to-metal adhesion strength. Additionally, different surface texturing patterns, such as micro-channel arrays and grid pattern, are produced by single-pass or two-pass micro-rolling strategies. The effect of these texture patterns on adhesion strength is studied through single-lap-joint shear strength test. Results indicate that surface with micro-textures are able to achieve noticeable improvement in adhesion strength.

Design and Analysis of Spectrally Selective Patterned Thin-Film Cells

This paper outlines several techniques for systematic and efficient optimization as well as sensitivity assessment to fabrication tolerances of surface texturing patterns in thin film amorphous silicon (a-Si) solar cells. The aim is to achieve maximum absorption enhancement. The joint optimization of several geometrical parameters of a three-dimensional lattice of periodic square silver nanoparticles, and an absorbing thin layer of a-Si, using constrained optimization tools and numerical FDTD simulations is reported. Global and local optimization methods, such as the Broyden–Fletcher–Goldfarb–Shanno quasi-Newton method and simulated annealing, are employed concurrently for solving the inverse near-field radiation problem. The design of the silver-patterned solar panel is optimized to yield maximum average enhancement in photon absorption over the solar spectrum. The optimization techniques are expedited and improved using a novel nonuniform adaptive spectral sampling technique. Furthermore, the sensitivity of the optimally designed parameters of the solar structure is analyzed by postulating a probabilistic model for the errors introduced in the fabrication process. Monte Carlo simulations and unscented transform techniques are used for this purpose.

New advances on maskless electrochemical texturing (MECT) for tribological purposes

Surface texturing can be applied to improve tribological performance of mechanical contacts, in particular in the case of lubricated systems. The purpose of this work was to improve an alternative method for surface texturing based on electrochemical dissolution without previous masking of the workpiece named maskless electrochemical texturing (MECT). Electrochemical dissolution combines high speed, good reproducibility and high cost-benefit ratio, which are important factors when an industrial application of surface texturing is pursued. The use of electrical discharge machining (EDM) for the manufacturing of the MECT tools enabled different microtexture patterns to be produced. The cathodic tool was an AISI 430 ferritic stainless steel plate containing a pattern of microholes and covered with an insulating paint layer. The effect of important parameters such as the gap between electrodes, the applied voltage and the texturing time were evaluated. Different texturing patterns containing dots, trace-dots and chevrons were successfully obtained using a NaCl solution electrolyte. Tribological tests textured surfaces under starved liquid lubrication showed friction and wear reduction, when compared with a smooth surface.

Geometry Optimization of Textured Three-Dimensional Micro- Thrust Bearings

This paper presents an optimization study of the geometry of three-dimensional micro-thrust bearings in a wide range of convergence ratios. The optimization goal is the maximization of the bearing load carrying capacity. The bearings are modeled as micro-channels, consisting of a smooth moving wall (rotor), and a stationary wall (stator) with partial periodic rectangular texturing. The flow field is calculated from the numerical solution of the Navier-Stokes equations for incompressible isothermal flow; processing of the results yields the bearing load capacity and friction coefficient. The geometry of the textured channel is defined parametrically for several width-to-length ratios. Optimal texturing geometries are obtained by utilizing an optimization tool based on genetic algorithms, which is coupled to the CFD code. Here, the design variables define the bearing geometry and convergence ratio. To minimize the computational cost, a multi-objective approach is proposed, consisting in the simultaneous maximization of the load carrying capacity and minimization of the bearing convergence ratio. The optimal solutions, identified based on the concept of Pareto dominance, are equivalent to those of single-objective optimization problems for different convergence ratio values. The present results demonstrate that the characteristics of the optimal texturing patterns depend strongly on both the convergence ratio and the width-to-length ratio. Further, the optimal load carrying capacity increases at increasing convergence ratio, up to an optimal value, identified by the optimization procedure. Finally, proper surface texturing provides substantial load carrying capacity even for parallel or slightly diverging bearings. Based on the present results, we propose simple formulas for the design of textured micro-thrust bearings.

Modelling of Couette flow in microchannels with textured surfaces

The effects of surface texturing patterns on the Couette flow in microchannels with sliding surfaces are analysed by means of computational fluid dynamics simulations. Different types of patterns are analysed, as well as different microchannel sizes. This study is focused on synthetic patterns, such as the microgrooves that are manufactured on the surface of a rubber seal to improve its friction performance. Based on the numerical results, an average model for the Couette flow is proposed. This average flow model includes a correction flow factor that has a direct dependence with the relative roughness, computed as the ratio of the mean height of the patterns and the channel hydraulic diameter.

Geodesic-driven visual effects over complex surfaces

Texture mapping is an important technique for adding visual details to geometric models. Image-based texture mapping is the most popular approach, but it relies on pre-computed images which often limit their use to static effects. For adding dynamic effects, procedural-based texturing is more adequate. Since it rely on functions to describe texturing patterns, procedural texturing allows for a more compact representation and control of visual effects by a simple change of parameters. In this work we describe GeoTextures, an approach that uses geodesic distance fields defined from multiple sources at different locations over a model surface to place, advect, and combine procedural visual effects over complex surfaces. The use of geodesics extends the scope of common procedural textures which are usually limited to using spatial 3D coordinates or 2D texture coordinates. We illustrate the flexibility of our real-time approach with a range of visual effects, such as time-based propagation of weathering phenomena, transparency effects, and mesh displacement over surfaces with smooth silhouettes using hardware based tessellation available in current graphics cards.

Evolutionary Optimization of Micro-Thrust Bearings With Periodic Partial Trapezoidal Surface Texturing

An optimization study of trapezoidal surface texturing in slider micro-bearings, via computational fluid dynamics (CFD), is presented. The bearings are modeled as micro-channels, consisting of a moving and a stationary wall. The moving wall (rotor) is assumed smooth, while part of the stationary wall (stator) exhibits periodic dimples of trapezoidal form. The extent of the textured part of the stator and the dimple geometry are defined parametrically; thus, a wide range of texturing configurations is considered. Flow simulations are based on the numerical solution of the Navier–Stokes equations for incompressible isothermal flow. To optimize the bearing performance, an optimization problem is formulated and solved by coupling the CFD code with an optimization tool based on genetic algorithms and local search methods. Here, the design variables define the bearing geometry, while load carrying capacity is the objective function to be maximized. Optimized texturing geometries are obtained for the case of parallel bearings for several numbers of dimples, illustrating significant load carrying capacity levels. Further, these optimized texturing patterns are applied to converging bearings for different convergence ratio values; the results demonstrate that, for small and moderate convergence ratios, a substantial increase in load carrying capacity, in comparison to smooth bearings, is obtained. Finally, an optimization study performed at a high convergence ratio shows that, in comparison to the parallel slider, the optimal texturing geometry is substantially different, and that performance improvement over smooth bearings is possible even for steep sliders.

Effect of Surface Texturing on Very Thin Film EHD Lubricated Contacts

Micro-dents of various depths and shapes have been produced on rubbing surfaces to find out whether there could be some operational conditions suitable for surface texturing applications in highly loaded non-conformal contacts. The significant effect of the size and shape of the micro-dents has been observed as a function of the slide-to-roll ratio. Shallow micro-features within concentrated contact were found to increase the film thickness by supplying more lubricant to the contact under rolling/sliding conditions. However, in many cases this effect was accompanied with local film thickness reduction that even caused lubrication film breakdown under thin film lubrication conditions. Longitudinally and transversely oriented short grooves were found not to be completely suitable for the surface texturing applications from this point of view. Conversely, small circular micro-dents seem to be more promising as to their use to help to separate rubbing surfaces when a micro-textured surface is moving faster than a non-textured one and the lubrication films become very thin. Nevertheless, it would require a well-balanced design, taking into account many factors as the lubrication regime, the slide-to-roll ratio conditions, the rolling contact fatigue, the technology of surface texturing patterns creation, etc.