scholarly journals The use of clamping grips and friction pads by tree frogs for climbing curved surfaces

2017 ◽  
Vol 284 (1849) ◽  
pp. 20162867 ◽  
Author(s):  
Thomas Endlein ◽  
Aihong Ji ◽  
Shanshan Yuan ◽  
Iain Hill ◽  
Huan Wang ◽  
...  
Keyword(s):  
Contact Area ◽  
Shear Stresses ◽  
Curved Surfaces ◽  
Sem Images ◽  
Flat Surfaces ◽  
Normal Forces ◽  
Adhesive Surface ◽  
Reaction Forces ◽  
Adhesive Pads ◽  
Tree Frogs

Most studies on the adhesive mechanisms of climbing animals have addressed attachment against flat surfaces, yet many animals can climb highly curved surfaces, like twigs and small branches. Here we investigated whether tree frogs use a clamping grip by recording the ground reaction forces on a cylindrical object with either a smooth or anti-adhesive, rough surface. Furthermore, we measured the contact area of fore and hindlimbs against differently sized transparent cylinders and the forces of individual pads and subarticular tubercles in restrained animals. Our study revealed that frogs use friction and normal forces of roughly a similar magnitude for holding on to cylindrical objects. When challenged with climbing a non-adhesive surface, the compressive forces between opposite legs nearly doubled, indicating a stronger clamping grip. In contrast to climbing flat surfaces, frogs increased the contact area on all limbs by engaging not just adhesive pads but also subarticular tubercles on curved surfaces. Our force measurements showed that tubercles can withstand larger shear stresses than pads. SEM images of tubercles revealed a similar structure to that of toe pads including the presence of nanopillars, though channels surrounding epithelial cells were less pronounced. The tubercles' smaller size, proximal location on the toes and shallow cells make them probably less prone to buckling and thus ideal for gripping curved surfaces.

scholarly journals Adsorption of Polymer-Grafted Nanoparticles on Curved Surfaces

Chemistry ◽  
2021 ◽  
Vol 3 (1) ◽  
pp. 382-390
Author(s):  
Aye Ozmaian ◽  
Rob D. Coalson ◽  
Masoumeh Ozmaian
Keyword(s):  
Self Assembly ◽  
Flat Surface ◽  
Separation Distance ◽  
Polymer Chains ◽  
Coarse Grained ◽  
Curved Surfaces ◽  
Flat Surfaces ◽  
Adhesive Surface ◽  
Grafted Nanoparticles ◽  
Pulling Force

Nanometer-curved surfaces are abundant in biological systems as well as in nano-sized technologies. Properly functionalized polymer-grafted nanoparticles (PGNs) adhere to surfaces with different geometries and curvatures. This work explores some of the energetic and mechanical characteristics of the adhesion of PGNs to surfaces with positive, negative and zero curvatures using Coarse-Grained Molecular Dynamics (CGMD) simulations. Our calculated free energies of binding of the PGN to the curved and flat surfaces as a function of separation distance show that curvature of the surface critically impacts the adhesion strength. We find that the flat surface is the most adhesive, and the concave surface is the least adhesive surface. This somewhat counterintuitive finding suggests that while a bare nanoparticle is more likely to adhere to a positively curved surface than a flat surface, grafting polymer chains to the nanoparticle surface inverts this behavior. Moreover, we studied the rheological behavior of PGN upon separation from the flat and curved surfaces under external pulling force. The results presented herein can be exploited in drug delivery and self-assembly applications.

scholarly journals Sticking like sticky tape: tree frogs use friction forces to enhance attachment on overhanging surfaces

2013 ◽  
Vol 10 (80) ◽  
pp. 20120838 ◽  
Author(s):  
Thomas Endlein ◽  
Aihong Ji ◽  
Diana Samuel ◽  
Ning Yao ◽  
Zhongyuan Wang ◽  
...  
Keyword(s):  
Slope Angle ◽  
Three Dimensional ◽  
The Body ◽  
Adhesive Tape ◽  
Large Contribution ◽  
Lateral Direction ◽  
Friction Forces ◽  
Normal Forces ◽  
Adhesive Pads ◽  
Tree Frogs

To live and clamber about in an arboreal habitat, tree frogs have evolved adhesive pads on their toes. In addition, they often have long and slender legs to facilitate not only long jumps, but also to bridge gaps between leaves when climbing. Both adhesive pads and long limbs are used in conjunction, as we will show in this study. Previous research has shown that tree frogs change from a crouched posture (where the limbs are close to the body) to a sprawled posture with extended limbs when clinging on to steeper inclines such as vertical or overhanging slopes. We investigated this change in posture in White's tree frogs ( Litoria caerulea ) by challenging the frogs to cling onto a tiltable platform. The platform consisted of an array of 24 three-dimensional force transducers, which allowed us to measure the ground reaction forces of the frogs during a tilt. Starting from a crouched resting position, the normal forces on the forelimbs changed sign and became increasingly negative with increasing slope angle of the platform. At about 106°±12°, tilt of the platform the frogs reacted by extending one or two of their limbs outwards. At a steeper angle (131°±11°), the frogs spread out all their limbs sideways, with the hindlimbs stretched out to their maximum reach. Although the extension was strongest in the lateral direction, limbs were significantly extended in the fore–aft direction as well. With the extension of the limbs, the lateral forces increased relative to the normal forces. The large contribution of the in-plane forces helped to keep the angle between the force vector and the platform small. The Kendall theory for the peeling of adhesive tape predicts that smaller peel angles lead to higher attachment forces. We compare our data with the predictions of the Kendall model and discuss possible implications of the sliding of the pads on the surface. The forces were indeed much larger for smaller angles and thus can be explained by peeling theory.

scholarly journals Adsorption of Polymer-Grafted Nanoparticles on Curved Surfaces

2021 ◽  
Author(s):  
Aye Ozmaian ◽  
Rob D. Coalson ◽  
Masoumeh Ozmaian
Keyword(s):  
Self Assembly ◽  
Flat Surface ◽  
Separation Distance ◽  
Polymer Chains ◽  
Coarse Grained ◽  
Curved Surfaces ◽  
Flat Surfaces ◽  
Adhesive Surface ◽  
Grafted Nanoparticles ◽  
Pulling Force

Nanometer-curved surfaces are abundant in biological systems as well as in nano-sized technologies. Properly functionalized polymer-grafted nanoparticles (PGNs) adhere to surfaces with different geometries and curvatures. This work explores some of the energetic and mechanical characteristics of the adhesion of PGNs to surfaces with positive, negative and zero curvatures using Coarse-Grained Molecular Dynamics (CGMD) simulations. Our calculated free energies of binding of the PGN to the curved and flat surfaces as a function of separation distance show that curvature of the surfaces critically impacts the adhesion strength. We find that the flat surface is the most adhesive, and the concave surface is the least adhesive surface. This somewhat counterintuitive finding suggests that while a bare nanoparticle is more likely to adhere to a positively curved surface than a flat surface, grafting polymer chains to the nanoparticle surface inverts this behavior. Moreover, we studied the rheological behavior of PGN upon separation from the flat and curved surfaces under external pulling force. The results presented herein can be exploited in drug delivery and self-assembly applications.

scholarly journals A Computational Model for the Analysis of Spreading of Viscoelastic Droplets over Flat Surfaces

Fluids ◽  
2018 ◽  
Vol 3 (4) ◽  
pp. 78 ◽  
Author(s):  
Aleck H. Alexopoulos ◽  
Costas Kiparissides
Keyword(s):  
Hyaluronic Acid ◽  
Acid Solution ◽  
Computational Model ◽  
Macroscopic Model ◽  
Curved Surfaces ◽  
Droplet Spreading ◽  
Flat Surfaces ◽  
Elastic Forces ◽  
Linear Viscoelastic ◽  
Linear Viscoelastic Fluid

The spreading of viscous and viscoelastic fluids on flat and curved surfaces is an important problem in many industrial and biomedical processes. In this work the spreading of a linear viscoelastic fluid with changing rheological properties over flat surfaces is investigated via a macroscopic model. The computational model is based on a macroscopic mathematical description of the gravitational, capillary, viscous, and elastic forces. The dynamics of droplet spreading are determined in sessile and pendant configurations for different droplet extrusion or formation times for a hyaluronic acid solution undergoing gelation. The computational model is employed to describe the spreading of hydrogel droplets for different extrusion times, droplet volumes, and surface/droplet configurations. The effect of extrusion time is shown to be significant in the rate and extent of spreading.

scholarly journals Experimental Investigations of Magnetic Abrasive Finishing on Titanium

2019 ◽  
Vol 4 (2) ◽  
Author(s):  
Shadab Ahmad ◽  
Ranganath M Singari ◽  
R S Mishra
Keyword(s):  
Surface Morphology ◽  
Material Removal ◽  
Experimental Investigations ◽  
Sem Images ◽  
Magnetic Abrasive Finishing ◽  
Flat Surfaces ◽  
Abrasive Finishing ◽  
Finished Surface ◽  
Titanium Material ◽  
Finishing Processes

Magnetic abrasive finishing (MAF) is one of the finishing processes which produces nano finished surfaces. The material removal process is in the form of microchips. The present paper introduces a novel work based on the principle of MAF for flat surfaces. The experiments were conducted on titanium material to investigate the response of MAF on hardness. Matlab has been used to evaluate the performance. The results obtained from the experimental investigations revealed that the hardness improves with MAF. The surface morphology of finished surface was studied with the help of SEM images

Development of a hydraulic driven bionic soft gecko toe

2021 ◽  
pp. 1-18
Author(s):  
Mingyue Lu ◽  
Guangming Chen ◽  
Qingsong He ◽  
Weijia Zong ◽  
Zhiwei Yu ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Low Cost ◽  
Hydraulic Pressure ◽  
Curved Surfaces ◽  
Type B ◽  
Surface Conditions ◽  
Flat Surfaces ◽  
Soft Actuator ◽  
Output Force

Abstract Geckos can climb freely on various types of surfaces using their flexible and adhesive toes. Gecko-inspired robots are capable of climbing on different surface conditions and have shown many important applications. Nonetheless, due to poor flexibility of toes the movements of gecko-inspired robots are restricted to flat surfaces. To improve the flexibility, by utilizing design technique of soft actuator and incorporating the characteristics of a real gecko's toe, the design of new bionic soft toes is proposed. The abilities of this bionic toe are verified using modelling and two soft toes are manufactured. One is Type A toe having varied semi-circle cross-sections as the feature of real gecko toe and the other is Type B toe with a constant semi-circle cross-section. The bending behaviors of the bionic toes subjected to a range of hydraulic pressure are also experimentally studied. It demonstrated that both toes can perform similarly large bending angles for the adduction (attachment) and abduction (detachment) motions. In comparisons, Type B toe exhibits larger output force, which is ascribed to the fact that at proximal section of Type B corresponds to larger volume for bearing fluid. Both toes can not only provide sufficient adhesion, but can be quickly detached with low peeling forces. Finally, different curved surfaces are used to further justify the applicability of these bionic toes. In particular, the flexible toes developed also have the advantages of low cost, lightweight, and simple control, which is desirable for wall-climbing robots.

Detachment Criterion for Static Axisymmetric Bubbles on Horizontal Flat Surfaces

2009 ◽  
Author(s):  
Shong-Leih Lee ◽  
Chao-Fu Yang
Keyword(s):  
Contact Area ◽  
Contact Angles ◽  
Maximum Volume ◽  
Flat Surfaces ◽  
Bubble Detachment ◽  
Numerical Result ◽  
Detachment Criterion ◽  
The Stability ◽  
The Many ◽  
Maximum Contact

The static Young-Laplace equation is solved with the geometry method to yield the bubble shape on a horizontal flat surface under various contact angles. Multi-solution modes are found. Among the many possible equilibrium shapes of the bubble, however, only the fundamental solution mode could occur naturally. The value of VAR (volume to contact area ratio) could be a good measure for stability of equilibrium bubbles. The bubble becomes less stable when VAR increases. The numerical result reveals that in the course of bubble growth (i.e. volume increases) the VAR of the bubble increases linearly until the maximum contact area is reached. After that, VAR has a sharp increase due to a decreasing contact area. Beyond the maximum volume, equilibrium bubble does not seem possible. Based on the finding, it is postulated that bubble detachment occurs somewhere between the maximum contact area and the maximum volume according to perturbations from environment. However, the postulation seems to underestimate the stability of the bubble significantly for contact angles of larger than 160 degrees. A correction is proposed in the paper. Numerical result of bubble detachment criterion is fitted with polynomial functions of the contact angle.

Spin moment calculation and its importance in railway dynamics

2009 ◽  
Vol 223 (5) ◽  
pp. 453-460 ◽  
Author(s):  
A Alonso ◽  
J G Giménez ◽  
L M Martín
Keyword(s):  
Contact Problem ◽  
Contact Area ◽  
Vehicle Dynamics ◽  
Contact Forces ◽  
Dissipated Energy ◽  
Shear Stresses ◽  
Spin Moment ◽  
Railway Dynamics ◽  
Tangential Contact ◽  
Original Algorithm

The objective of this work is to analyse the influence of the spin moment generated at the wheel—rail contact area on both vehicle dynamics and dissipated energy that is closely related to wear. From the different methods used in railway simulation programs to model the tangential contact problem, FastSim algorithm has been selected in this work due to its accuracy in the calculation of the contact forces and also because it allows obtaining the spin moment integrating the shear stresses. In the first part of the article the accuracy of FastSim in the calculation of spin moment is analysed. Also, some modifications are introduced in the original algorithm in order to improve its accuracy. In the second part, the influence of the spin moment on the results of some typical situations is presented. It has been checked that its influence on railway dynamics is negligible. On the contrary, it has been found that the value of the dissipated energy can be greatly modified if this parameter is taken into account.

Analytical Studies of Contact of Nominally Flat Surfaces; Effect of Previous Loading

1971 ◽  
Vol 93 (4) ◽  
pp. 451-456 ◽  
Author(s):  
B. Mikic
Keyword(s):  
Size Distribution ◽  
Contact Area ◽  
Thermal Contact ◽  
Thermal Contact Conductance ◽  
Contact Conductance ◽  
Flat Surfaces ◽  
Analytical Studies ◽  
Previous Loading

This work analytically investigates effect of previous loading on contact area, number of contact prints, their size distribution, and the value of thermal contact conductance for two nominally flat surfaces in contact. The model used in the analysis assumes that the surfaces are Gaussian and that in the first loading deformation of the surface asperities is plastic.

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