Inversion of friction anisotropy in a bio-inspired asymmetrically structured surface

Friction anisotropy is an important property of many surfaces that usually facilitate the generation of motion in a preferred direction. Such surfaces are very common in biological systems and have been the templates for various bio-inspired materials with similar tribological properties. So far friction anisotropy is considered to be the result of an asymmetric arrangement of surface nano- and microstructures. However, here we show by using bio-inspired sawtooth-structured surfaces that the anisotropic friction properties are not only controlled by an asymmetric surface topography, but also by the ratio of the sample–substrate stiffness, the aspect ratio of surface structures, and by the substrate roughness. Systematically modifying these parameters, we were able to demonstrate a broad range of friction anisotropies, and for specific sample–substrate combinations even an inversion of the anisotropy. This result highlights the complex interrelation between the different material and topographical parameters on friction properties and sheds new light on the conventional design paradigm of tribological systems. Finally, this result is also of great importance for understanding functional principles of biological materials and surfaces, as such inversion of friction anisotropy may correlate with gait pattern and walking behaviour in climbing animals, which in turn may be used in robotic applications.

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Getting grip in changing environments: the effect of friction anisotropy inversion on robot locomotion

Applied Physics A ◽

10.1007/s00339-021-04443-7 ◽

2021 ◽

Vol 127 (5) ◽

Author(s):

Halvor T. Tramsen ◽

Lars Heepe ◽

Jettanan Homchanthanakul ◽

Florentin Wörgötter ◽

Stanislav N. Gorb ◽

...

Keyword(s):

Energy Efficient ◽

Legged Locomotion ◽

Hexapod Robot ◽

Friction Anisotropy ◽

Anisotropic Friction ◽

Walking Behavior ◽

Robot Locomotion ◽

Computational Morphology ◽

Anisotropic Structures ◽

Walking Environment

AbstractLegged locomotion of robots can be greatly improved by bioinspired tribological structures and by applying the principles of computational morphology to achieve fast and energy-efficient walking. In a previous research, we mounted shark skin on the belly of a hexapod robot to show that the passive anisotropic friction properties of this structure enhance locomotion efficiency, resulting in a stronger grip on varying walking surfaces. This study builds upon these results by using a previously investigated sawtooth structure as a model surface on a legged robot to systematically examine the influences of different material and surface properties on the resulting friction coefficients and the walking behavior of the robot. By employing different surfaces and by varying the stiffness and orientation of the anisotropic structures, we conclude that with having prior knowledge about the walking environment in combination with the tribological properties of these structures, we can greatly improve the robot’s locomotion efficiency.

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Hierarchical Nano/Micro-structured Surfaces with High Surface Area/Volume Ratios

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4049850 ◽

2021 ◽

pp. 1-36

Author(s):

Ketki Lichade ◽

Yizhou Jiang ◽

Yayue Pan

Keyword(s):

Surface Structure ◽

Surface Area ◽

Light Trapping ◽

High Surface ◽

High Surface Area ◽

Three Dimensional ◽

Structure Design ◽

Surface Structures ◽

Structured Surfaces ◽

Design And Manufacture

Abstract Recently, many studies have investigated additive manufacturing of hierarchical surfaces with high surface area/volume (SA/V) ratios, and their performance has been characterized for applications in next-generation functional devices. Despite recent advances, it remains challenging to design and manufacture high SA/V ratio structures with desired functionalities. In this study, we established the complex correlations among the SA/V ratio, surface structure geometry, functionality, and manufacturability in the Two-Photon Polymerization (TPP) process. Inspired by numerous natural structures, we proposed a 3-level hierarchical structure design along with the mathematical modeling of the SA/V ratio. Geometric and manufacturing constraints were modeled to create well-defined three-dimensional hierarchically structured surfaces with a high accuracy. A process flowchart was developed to design the proposed surface structures to achieve the target functionality, SA/V ratio, and geometric accuracy. Surfaces with varied SA/V ratios and hierarchy levels were designed and printed. The wettability and antireflection properties of the fabricated surfaces were characterized. It was observed that the wetting and antireflection properties of the 3-level design could be easily tailored by adjusting the design parameter settings and hierarchy levels. Furthermore, the proposed surface structure could change a naturally-hydrophilic surface to near-superhydrophobic. Geometrical light trapping effects were enabled and the antireflection property could be significantly enhanced (>80% less reflection) by the proposed hierarchical surface structures. Experimental results implied the great potential of the proposed surface structures for various applications such as microfluidics, optics, energy, and interfaces.

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Application of variothermal heating concepts for the production of microstructured films using the extrusion embossing process

Journal of Polymer Engineering ◽

10.1515/polyeng-2012-0502 ◽

2012 ◽

Vol 32 (2) ◽

Cited By ~ 2

Author(s):

Walter Michaeli ◽

Stephan Eilbracht ◽

Micha Scharf ◽

Claudia Hartmann ◽

Kirsten Bobzin ◽

...

Keyword(s):

Temperature Profile ◽

Large Scale ◽

Cost Effective ◽

Processing Parameters ◽

Surface Structures ◽

Structured Surfaces ◽

Heating Systems ◽

External Heating

Abstract The application of the extrusion embossing process is a fast and cost-effective way to produce large-scale films with structured surfaces. In principle, microscopic and macroscopic surface structures can be manufactured this way. Particularly for the fabrication of microscopic structures, the reproduction accuracy can be remarkably improved by applying variothermal heating concepts for the embossing roll. In this article, two possible heating concepts are investigated: one laser-based and another using an inductor. The generated temperature profile along the circumference of the embossing roll is studied, taking the material of the embossing roll as well as different processing parameters into account. Both external heating systems (laser vs. inductor) are tested and compared. Furthermore, the improvement of the accuracy of the replicated microstructures is examined.

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Durable superoleophobic polypropylene surfaces

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2016.0193 ◽

2016 ◽

Vol 374 (2073) ◽

pp. 20160193 ◽

Cited By ~ 25

Author(s):

Philip S. Brown ◽

Bharat Bhushan

Keyword(s):

High Temperature ◽

Plastic Material ◽

Polymer Surface ◽

Polymer Surfaces ◽

Surface Structures ◽

Structured Surfaces ◽

Mechanical Durability ◽

Plastic Containers

Polypropylene (PP) is a popular plastic material used in consumer packaging. It would be desirable if such plastic containers were liquid repellent and not so easily fouled by their contents. Existing examples of superoleophobic surfaces typically rely on poorly adhered coatings or delicate surface structures, resulting in poor mechanical durability. Here, we report a facile method for creating superoleophobic PP surfaces via incorporation of nanoparticles (NPs) into the polymer surface. A solvent–NP–PP mixture was spin coated at high temperature to achieve the necessary roughness. Such surfaces were further functionalized with fluorosilane to result in a durable, super-repellent surface. They were also found to exhibit some repellency towards shampoos. This method of incorporating NPs into polymer surfaces could also prove useful in improving the anti-bacterial, mechanical and liquid-repellent properties of plastic devices. This article is part of the themed issue ‘Bioinspired hierarchically structured surfaces for green science’.

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Influence of laser hardening on laser induced periodic surface structures on steel substrates

IOP Conference Series Materials Science and Engineering ◽

10.1088/1757-899x/1135/1/012024 ◽

2021 ◽

Vol 1135 (1) ◽

pp. 012024

Author(s):

Lewin Rathmann ◽

Tim Radel

Keyword(s):

Thermal Load ◽

Laser Power ◽

Contact Angles ◽

High Ratio ◽

Laser Hardening ◽

Surface Structures ◽

Single Droplet ◽

Periodic Surface ◽

Structured Surfaces ◽

Steel Substrates

Abstract Laser-induced periodic surface structures (LIPSS) are used to structure surfaces for functionalization. Thus, hydrophilic states are generated using LIPSS. However, these nanostructures do not withstand mechanical loads and therefore cannot be used for most tribological applications. Within this work the approach of laser hardening of LIPSS is investigated. It is shown that laser hardening leads to an alteration of prior structured surfaces. That effects the wetting behaviour. The higher the laser power during hardening, the more increases the contact angle of a single droplet on the surface and the more the surface lacks in terms of wetting behaviour. This phenomenon is attributed to changes in LIPSS’ aspect ratio. A high ratio leads to low contact angles and is shifted to low values when the laser power increases resulting in high contact angles. Hence, it is concluded that the thermal load during laser hardening, and it’s influence on the wettability must be taken into account when LIPSS are subjected to laser hardening.

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Gait Pattern Based on CMAC Neural Network for Robotic Applications

Neural Processing Letters ◽

10.1007/s11063-012-9257-6 ◽

2012 ◽

Vol 38 (2) ◽

pp. 261-279 ◽

Cited By ~ 2

Author(s):

Christophe Sabourin ◽

Weiwei Yu ◽

Kurosh Madani

Keyword(s):

Neural Network ◽

Gait Pattern ◽

Cmac Neural Network ◽

Robotic Applications

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Acquisition of Heuristic Knowledge for the Prediction of the Frictional Behavior of Surface Structures Created by Self-Excited Tool Vibrations

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.504-506.963 ◽

2012 ◽

Vol 504-506 ◽

pp. 963-968 ◽

Cited By ~ 5

Author(s):

Thilo Breitsprecher ◽

Rouven Hense ◽

Franz Hauer ◽

Sandro Wartzack ◽

Dirk Biermann ◽

...

Keyword(s):

Data Mining ◽

Metal Forming ◽

Process Development ◽

Expert Knowledge ◽

Surface Structures ◽

Full Potential ◽

Forming Process ◽

Structured Surfaces ◽

Frictional Behavior ◽

Tool Vibrations

The selective control of the frictional behavior (tailored friction) in metal forming processes is of high importance with regard to technical and economic aspects. This applies especially for the sheet-bulk-metal forming process. Milling with intentionally invoked regenerative tool vibrations can be applied in order to generate structured surfaces with tailored friction properties on the forming tool. These structures affect the formation of lubrication pockets during the forming process which determine the local frictional properties exceedingly. The full potential of this emerging technology can, however, only be revealed if the heuristic and design-relevant knowledge is acquired and provided to the tool-designer already in the early phases of process development. One thing the tool-designer has to specify is the local frictional behavior on the tool surface. But, however, he does not know which milling parameters lead to the necessary surface structures because in most cases he has no expert knowledge in milling, tribology and forming tools. In this paper data mining is used to determine the frictional behavior based on these parameters. The potential of this method in the described context is revealed by the application on data derived from simulation results, both from milling simulations and contact simulations. The latter are performed by using a Halfspace model for rough surface contact. Both approaches for these simulations, the data mining process and the results are explained to the reader.

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Mass production of bio-inspired structured surfaces

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1243/09544062jmes540 ◽

2007 ◽

Vol 221 (10) ◽

pp. 1181-1191 ◽

Cited By ~ 23

Author(s):

S J Abbott ◽

P H Gaskell

Keyword(s):

Mass Production ◽

Basic Science ◽

Surface Structures ◽

Current Understanding ◽

Machine integrated telecentric surface metrology in laser structuring systems

ACTA IMEKO ◽

10.21014/acta_imeko.v2i2.106 ◽

2014 ◽

Vol 2 (2) ◽

pp. 73 ◽

Cited By ~ 2

Author(s):

Robert Schmitt ◽

Tilo Pfeifer ◽

Guilherme Mallmann

Keyword(s):

Closed Loop ◽

Optical Measurement ◽

Surface Structures ◽

Innovative Technology ◽

Surface Metrology ◽

Closed Loop Control ◽

Loop Control ◽

Structured Surfaces ◽

Laser Structuring ◽

Micro Structures

The laser structuring is an innovative technology used in a broad spectrum of industrial branches. There is, however, a market trend to smaller and more accurate micro structures, which demands a higher level of precision and efficiency in this process. In this terms, an inline inspection is necessary, in order to improve the process through a closed-loop control and early defect detection. Within this paper an optical measurement system for inline inspection of micro and macro surface structures is described. Measurements on standards and laser structured surfaces are presented, which underline the potential of this technique for inline surface inspection of laser structured surfaces.

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Anisotropic Friction in Cold Rolling of Flat Steel Strips

World Tribology Congress III, Volume 1 ◽

10.1115/wtc2005-63986 ◽

2005 ◽

Cited By ~ 1

Author(s):

N. Legrand ◽

B. Becker

Keyword(s):

Cold Rolling ◽

Rolling Direction ◽

Work Roll ◽

Friction Anisotropy ◽

Anisotropic Friction ◽

Steel Strips ◽

Flat Steel ◽

Cold Rolled ◽

Suitable Process

This work analysed the role of friction and other process parameters on strip edge drop and width variations during cold rolling of flat steel strips. Comparisons of 3D numerical simulations with experimental datas from rolling trials have shown that roll bite friction is anisotropic: friction in the transverse direction is twice to four times higher than that in the rolling direction. Work roll circumferential grinding striations and the associated roll roughness anisotropy are considered to be responsible for this anisotropy. Moreover by modifying friction anisotropy (decrease of transverse friction for the same longitudinal friction), it is possible to compensate for width narrowing usually observed on commercial cold mills (narrowing is due to strip thermal contractions in the mill interstands). Therefore, friction appears as a suitable process actuator for control of cold rolled product dimensions.

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