scholarly journals Physical principles of fluid-mediated insect attachment - Shouldn’t insects slip?

2014 ◽  
Vol 5 ◽  
pp. 1160-1166 ◽  
Author(s):  
Jan-Henning Dirks
Keyword(s):  
Static Friction ◽  
Friction Forces ◽  
Wet Adhesion ◽  
Adhesive Pads ◽  
Adhesion Model ◽  
Attachment Model ◽  
Rigid Surfaces ◽  
Physical Principles ◽  
Insect Attachment ◽  
Adhesive Fluid

Insects use either hairy or smooth adhesive pads to safely adhere to various kinds of surfaces. Although the two types of adhesive pads are morphologically different, they both form contact with the substrate via a thin layer of adhesive fluid. To model adhesion and friction forces generated by insect footpads often a simple “wet adhesion” model is used, in which two flat undeformable substrates are separated by a continuous layer of fluid. This review summarizes the key physical and tribological principles that determine the adhesion and friction in such a model. Interestingly, such a simple wet-adhesion model falls short in explaining several features of insect adhesion. For example, it cannot predict the observed high static friction forces of the insects, which enable them to cling to vertical smooth substrates without sliding. When taking a closer look at the “classic” attachment model, one can see that it is based on several simplifications, such as rigid surfaces or continuous layers of Newtonian fluids. Recent experiments show that these assumptions are not valid in many cases of insect adhesion. Future tribological models for insect adhesion thus need to incorporate deformable adhesive pads, non-Newtonian properties of the adhesive fluid and/or partially “dry” or solid-like contact between the pad and the substrate.

scholarly journals Slipping–rolling transitions of a body with two contact points

2021 ◽  
Author(s):  
Mate Antali ◽  
Gabor Stepan
Keyword(s):  
Rigid Body ◽  
Contact Point ◽  
Static Friction ◽  
Rigid Body Dynamics ◽  
Contact Forces ◽  
Friction Forces ◽  
Contact Points ◽  
Body Dynamics ◽  
Coulomb Model ◽  
Rigid Surfaces

AbstractIn this paper, the general kinematics and dynamics of a rigid body is analysed, which is in contact with two rigid surfaces in the presence of dry friction. Due to the rolling or slipping state at each contact point, four kinematic scenarios occur. In the two-point rolling case, the contact forces are undetermined; consequently, the condition of the static friction forces cannot be checked from the Coulomb model to decide whether two-point rolling is possible. However, this issue can be resolved within the scope of rigid body dynamics by analysing the nonsmooth vector field of the system at the possible transitions between slipping and rolling. Based on the concept of limit directions of codimension-2 discontinuities, a method is presented to determine the conditions when the two-point rolling is realizable without slipping.

MEASUREMENT OF THE STATIC FRICTION COEFFICIENT BETWEEN A poly-V belt 5pk AND A PULLEY UNDER DRY CONDITIONS

Tribologia ◽  
2018 ◽  
Vol 277 (1) ◽  
pp. 57-62
Author(s):  
Krzysztof KUBAS
Keyword(s):  
Friction Coefficient ◽  
Nonlinear Function ◽  
Static Friction ◽  
Friction Forces ◽  
Good Accordance ◽  
Dry Conditions ◽  
Rest Time ◽  
Wrap Angle ◽  
Different Shapes ◽  
Static Coefficient

The paper presents the results of experimental measurements of static friction forces between a poly-V belt 5pk and a pulley on a specialised research stand. An average effective static coefficient is assumed depending on the wrap angle and preload force. Different shapes and positions of curves of the measured values for lower wrap angles are found, with similar curves in the set of measurements with higher angles. The Nelder-Mead optimisation method is proposed to approximate the measured results by a nonlinear function and to achieve good accordance. The dependence of the effective friction coefficient on the rest time between measurements is also presented.

Modeling the Effect of Surface Roughness on the Adhesion, Contact and Friction in Micro-Electro-Mechanical Systems (MEMS) Interfaces

2003 ◽  
Author(s):  
Noureddine Tayebi ◽  
Andreas A. Polycarpou
Keyword(s):  
Surface Texturing ◽  
Static Friction ◽  
Normal Operation ◽  
Root Mean Square Roughness ◽  
Adhesion Forces ◽  
Sensors And Actuators ◽  
Micro Electro Mechanical Systems ◽  
Friction Forces ◽  
Normal Forces ◽  
Adhesion Contact

It has been experimentally shown that surface texturing (roughening) decreases the effect of intermolecular adhesion forces that are significant in MEMS applications. These forces can hinder normal operation of sensors and actuators as well as micro-engines where they might increase friction, which could be catastrophic. In this paper, a model that predicts the effects of roughness, asymmetry, and flatness on the adhesion, contact, and friction forces in MEMS interfaces is presented. The three key parameters used to characterize the roughness the asymmetry and the flatness of a surface topography are the root-mean-square roughness (RMS), skewness and kurtosis, respectively. It is predicted that surfaces with high RMS, high kurtosis and positive skewness exhibit lower adhesion and static friction coefficient, even at extremely low external normal forces.

Lubricant Performance in Magnetic Thin Film Disks With Carbon Overcoat—Part I: Dynamic and Static Friction

1991 ◽  
Vol 113 (1) ◽  
pp. 22-31 ◽  
Author(s):  
J. L. Streator ◽  
B. Bhushan ◽  
D. B. Bogy
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Static Friction ◽  
Disk Surface ◽  
Stick Slip ◽  
Sliding Speed ◽  
Friction Coefficients ◽  
Friction Forces ◽  
Strong Adhesion ◽  
Lubricant Viscosity

Static and dynamic friction coefficients are presented for an Al2O3·TiC slider in contact with 130 mm carbon-coated rigid thin film disks lubricated with several different perfluoropolyether lubricants. The lubricants tested include three nonpolar liquid lubricants and one polar liquid lubricant with dihydroxyl end groups. The effects of lubricant film thickness, disk surface topography, sliding speed and lubricant viscosity are investigated. In many cases, the interfaces exhibited a sharp increase in the dynamic and static friction coefficients after a certain film thickness was reached, due to strong adhesion in the interface. In most cases, the lubricant thickness for the onset of high friction forces was found to increase with increasing disk surface roughness, lubricant viscosity and sliding speed. Under certain conditions stick/slip of the slider occurred during which the static friction increased with time of contact. The various data suggest that the rate at which strong adhesion develops depends on the lubricant viscosity.

Atomistics of Friction

2005 ◽  
Author(s):  
Motohisa Hirano
Keyword(s):  
Friction Force ◽  
Translational Motion ◽  
Static Friction ◽  
System Size ◽  
Dynamic Friction ◽  
Friction Forces ◽  
Internal Motions ◽  
Locking Mechanism ◽  
Roughness Model ◽  
Solid Bodies

The atomistic mechanisms are proposed for the origin of the static and the dynamic friction forces. The mechanism for the origin of the static friction force resembles the mechanical locking mechanism in a surface roughness model. The origin of the dynamic friction force is formulated as a problem of how the given translational kinetic energy dissipates into the internal relative motions of constituent atoms of bodies during sliding. From studying that the available phase space volume of the translational motion becomes negligible small for a large system size, compared with that of the internal motions, it is concluded that the energy dissipation occurs irreversibly from the translational motion to the internal motions. A phenomenon of superlubricity, where two solid bodies move relatively with no resistance, is discussed.

Analytical and Experimental Analysis of Static Friction Forces of Moving Cables Inside Curved Pipes

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Eduardo A. W. de Menezes ◽  
Filipe P. Geiger ◽  
Eduardo A. Perondi ◽  
Javier M. Fernández ◽  
Hugo F. L. Santos
Keyword(s):  
Experimental Tests ◽  
Static Friction ◽  
Polymeric Coating ◽  
General Strategy ◽  
Friction Forces ◽  
Simulation Performance ◽  
Curved Pipes ◽  
New Equation ◽  
Umbilical Cable ◽  
Hydrate Plug

In-pipe robots are a powerful tool for hydrate plug removal inside ultradeepwater pipes. Most of these robots operate with the energy supplied by umbilical cables. The present work focuses on the development of a general strategy for computing the required forces for pulling such cables confined in ducts of generic length and geometry. Based on classical mathematical models applied in cable friction evaluation, a new equation set was developed and implemented in a computational algorithm designed to evaluate the static friction force related to the cumulative effects along the arbitrary set of curves present in a generic pipe. Therefore, the proposed computational routine can calculate the static friction forces associated with a cable inside a given pipe, whose coordinates are fed by the user. To evaluate the simulation performance, the achieved results were compared with the data obtained through experimental tests performed using a cable with polymeric coating positioned inside ducts. Different geometries, loads, and lubricating conditions were tested, and the analytical model could suitably estimate the required force to move an umbilical cable inside pipes.

scholarly journals Insect tricks: two-phasic foot pad secretion prevents slipping

2009 ◽  
Vol 7 (45) ◽  
pp. 587-593 ◽  
Author(s):  
Jan-Henning Dirks ◽  
Christofer J. Clemente ◽  
Walter Federle
Keyword(s):  
Adhesive System ◽  
Continuous Phase ◽  
Stick Insect ◽  
Force Measurements ◽  
Friction Forces ◽  
Adhesive Pads ◽  
Foot Pad ◽  
Detailed Function ◽  
Adhesive Secretion

Many insects cling to vertical and inverted surfaces with pads that adhere by nanometre-thin films of liquid secretion. This fluid is an emulsion, consisting of watery droplets in an oily continuous phase. The detailed function of its two-phasic nature has remained unclear. Here we show that the pad emulsion provides a mechanism that prevents insects from slipping on smooth substrates. We discovered that it is possible to manipulate the adhesive secretion in vivo using smooth polyimide substrates that selectively absorb its watery component. While thick layers of polyimide spin-coated onto glass removed all visible hydrophilic droplets, thin coatings left the emulsion in its typical form. Force measurements of stick insect pads sliding on these substrates demonstrated that the reduction of the watery phase resulted in a significant decrease in friction forces. Artificial control pads made of polydimethylsiloxane showed no difference when tested on the same substrates, confirming that the effect is caused by the insects’ fluid-based adhesive system. Our findings suggest that insect adhesive pads use emulsions with non-Newtonian properties, which may have been optimized by natural selection. Emulsions as adhesive secretions combine the benefits of ‘wet’ adhesion and resistance against shear forces.

The Role of Relative Humidity, Surface Roughness and Liquid Build-Up on Static Friction Behavior of the Head/Disk Interface

1993 ◽  
Vol 115 (1) ◽  
pp. 28-35 ◽  
Author(s):  
Hong Tian ◽  
Takeo Matsudaira
Keyword(s):  
Surface Roughness ◽  
Relative Humidity ◽  
Static Friction ◽  
Height Distribution ◽  
Head Disk Interface ◽  
Friction Behavior ◽  
Friction Forces ◽  
Disk Interface ◽  
Percent Relative Humidity

Stiction at the head/disk interface has become one of the major concerns as smoother surfaces are required to achieve lower flying heights of magnetic heads over magnetic disks. In this paper, static friction forces on three types of disk samples with different surface roughness values were measured at various relative humidities. It was found that static friction coefficients were well correlated with total thickness of liquid (lubricant and adsorbed water) at the head/disk interface. The experimental data also agreed fairly well with the calculated values based on a proposed stiction model. It is implied in the stiction model that the bearing ratio or the shape of asperity height distribution, especially the part of high asperities, determines the stiction force. Moreover, long-term stiction was investigated on the unlubricated disk surfaces at 80 percent relative humidity and on the lubricated disks at 5 percent relative humidity to separate the effects of water build-up and lubricant build-up at the head/disk interface. It appears that long-term stiction occurs only when enough mobile lubricant is present and the thickness of liquid at the head/disk interface is close to a critical thickness value which is related to surface roughness values.

Functional Morphology and Design Constraints of Smooth Adhesive Pads

MRS Bulletin ◽  
2007 ◽  
Vol 32 (6) ◽  
pp. 479-485 ◽  
Author(s):  
W. Jon. P. Barnes
Keyword(s):  
Fluid Layer ◽  
Adhesive Force ◽  
Average Thickness ◽  
Force Component ◽  
Design Constraints ◽  
Friction Forces ◽  
Adhesive Pads ◽  
Tree Frogs ◽  
Strong Attachment ◽  
Air Liquid Interface

AbstractSmooth adhesive pads are found among the arthropods, amphibians (particularly tree frogs), and in some mammals. They are used for dynamic adhesion when an animal is climbing steep or overhanging smooth surfaces. There is a need for strong attachment to avoid falling and easy detachment to enable the animal to move. This article describes the morphology and physical properties of smooth adhesive pads, stressing how there is little variation in structure, within tree frogs at least, even among pads that have evolved independently. This is clear evidence of an optimum design; best adhesion occurs when there is a continuous, thin film of fluid between the pad and the surface. Smooth adhesive pads adhere by wet adhesion, the main force component being capillarity, produced by the air/liquid interface (meniscus) around the edge of each pad. Smooth adhesive pads also produce substantial friction forces, probably because of actual contact between the pad surface and substrate (tree frogs) or non-Newtonian properties of the secreted fluid (insects). This is possible because the fluid layer beneath the pad has an average thickness of only a few nanometers. The article also discusses the scaling of adhesive force with size and, finally, implications for biomimetics.

scholarly journals Contact compliance effects in the frictional response of bioinspired fibrillar adhesives

2013 ◽  
Vol 10 (83) ◽  
pp. 20130182 ◽  
Author(s):  
Marco Piccardo ◽  
Antoine Chateauminois ◽  
Christian Fretigny ◽  
Nicola M. Pugno ◽  
Metin Sitti
Keyword(s):  
Shear Failure ◽  
Friction Mechanisms ◽  
Static Friction ◽  
Lateral Loading ◽  
Contact Interface ◽  
Friction Forces ◽  
Contact Compliance ◽  
Set Up ◽  
Fibrillar Adhesives

The shear failure and friction mechanisms of bioinspired adhesives consisting of elastomer arrays of microfibres terminated by mushroom-shaped tips are investigated in contact with a rigid lens. In order to reveal the interplay between the vertical and lateral loading directions, experiments are carried out using a custom friction set-up in which normal stiffness can be made either high or low when compared with the stiffness of the contact between the fibrillar adhesive and the lens. Using in situ contact imaging, the shear failure of the adhesive is found to involve two successive mechanisms: (i) cavitation and peeling at the contact interface between the mushroom-shaped fibre tip endings and the lens; and (ii) side re-adhesion of the fibre's stem to the lens. The extent of these mechanisms and their implications regarding static friction forces is found to depend on the crosstalk between the normal and lateral loading directions that can result in contact instabilities associated with fibre buckling. In addition, the effects of the viscoelastic behaviour of the polyurethane material on the rate dependence of the shear response of the adhesive are accounted for.

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