An experimental method for quantitative analysis of real contact area based on the total reflection optical principle

The simulation of real contact area between materials is foundationally important for the contact mechanics of mechanical structures. The Greenwood and Williamson(GW) model and the Majumdar(MB) model are the basic models in this field, which are widely accepted and proven to be valid in many experiments and engineering. Although the contact models have evolved considerably in recent years, the verifications of the models are most based on the indirect methods such as electrical conductivity and contact stiffness, because of the lack of effective methods to directly measure the variation of contact surface. In this paper, the total reflection(TR) method is introduced into the verification of contact models.An experiment system based on TR method is constructed to measure the real contact area of two PMMA specimens. The comparison analysis between the results of experiment and models suggests that the experiment result has the same trend with simulation, the MB model has better agreement with the experimental result because this method can take into account the variation of radius and the merging of asperities, while the GW model has a huge deviation because of the dependence on resolution and the lack of considering the variation of radius and asperity's merging process. Taking the interaction of asperities into account could give a better result that is closer to the experiment. Our results and analysis prove that the experimental methods in this paper could be used as a more direct and valid method to quantitatively measure the real contact area and to verify the contact models.

Evolution of real contact area during stick-slip movement observed by total reflection method

We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted to overcome the bending moment in the lateral friction movement. Besides some classical phenomena of stick-slip movement such as periodical slow increase of frictional force in sticking phase and a sudden drop when slipping, a special phenomenon that the contact area increases with the tangential force is observed, which was called junction growth by Tabor in 1959.Image processing methods are developed to observe the variation of the junction area. The results show that the center of the strongest contact region will keep sticking under the tangential force until the whole slipping, the strongest point undergoes three stages in one cycle, which are named as sticking stage, fretting stage, and cracking stage, respectively. The combined analysis reveals a physical process of stick-slip movement: the tangential force causes the increase of the real contact area, which reduces the pressure between the contact spots and finally leads to the slipping. Once slipping occurs,the real contact area drops to the original level resulting in the pressure increase to the original level, which makes the sticking happen again.

Experimental analysis of interface contact behavior using a novel image processing method

The spatial and temporal evolution of real contact area of contact interface with loads is a challenge.It is generally believed that there is a positive linear correlation between real contact area and normal load.However,with the development of measuring instruments and methods,some scholars have found that the growth rate of real contact area will slow down with the increase of normal load under certain conditions,such as large-scale interface contact with small roughness surface,which is called the nonlinear phenomenon of real contact area.At present,there is no unified conclusion on the explanation of this phenomenon.We set up an experimental apparatus based on the total reflection principle to verify this phenomenon and analyze its mechanism.An image processing method is proposed,which can be used to quantitative analysis micro contact behaviors on macro contact phenomenon.The weighted superposition method is used to identify micro contact spots,to calculate the real contact area,and the color superimposed image is used to identify micro contact behaviors.Based on this method,the spatiotemporal evolution mechanism of real contact area nonlinear phenomena is quantitatively analyzed.Furthermore,the influence of nonlinear phenomenon of real contact area on the whole loading and unloading process is analyzed experimentally.It is found that the effects of fluid between contact interface,normal load amplitude and initial contact state on contact behavior cannot be ignored in large-scale interface contact with small roughness surface.

Mechanism analysis and improved model for stick-slip friction behavior considering stress distribution variation of interface

Studying the evolution of interface contact state, revealing the “black box” behavior in interface friction and establishing a more accurate friction model are of great significance to improve the prediction accuracy of mechanical system performance. Based on the principle of total reflection, a visual analysis technology of interface contact behavior is proposed. Considering the dynamic variation of stress distribution in interface contact, we analyze the nonlinear characteristics of contact parameters in different stages of stick-slip process using the above-mentioned experimental technology. Then,we find that the tangential stiffness of the interface is not a fixed value during the stick-slip process and the stress distribution variation is one of the important factors affecting the tangential stiffness of interface. Based on the previous experimental results, we present an improved stick-slip friction model, considering the change of tangential stiffness and friction coefficient caused by the stress distribution variation. This improved model can characterize the variation characteristics of contact parameters in different stages of stick-slip process, whose simulation results are in good agreement with the experimental data. This research may be valuable for improving the prediction accuracy of mechanical system performance.

Excitation of the abdominal ganglion affects the electrophysiological activity of indirect flight muscles of the honeybee Apis mellifera

Our understanding of the nervous tissues that affect the wing flapping of insects mainly focuses on the brain,but wing flapping is a rhythmic movement related to the central pattern generator in the ventral nerve cord.To verify whether the neural activity of the abdominal ganglion of the honeybee(Apis mellifera)affects the flapping-wing flight,we profiled the response characteristics of indirect flight muscles to abdominal ganglion excitation.Strikingly,a change in the neural activity of ganglion 3 or ganglion 4 has a stronger effect on the electrophysiological activity of indirect flight muscles than that of ganglion 5.The electrophysiological activity of vertical indirect flight muscles is affected more by the change in neural activity of the abdominal ganglion than that of lateral indirect flight muscles.Moreover,the change in neural activity of the abdominal ganglion mainly causes the change in the muscular activity of indirect wing muscles,but the activity patterns change relatively little and there is little change in the complicated details.This work improves our understanding of the neuroregulatory mechanisms associated with the flapping-wing flight of honeybees.

Development of wet adhesion of honeybee arolium incorporated polygonal structure with three-phase composite interfaces

Inspired by the dynamic wet adhesive systems in nature,various artificial adhesive surfaces have been developed but still face different challenges.Crucially,the theoretical mechanics of wet adhesives has never been sufficiently revealed.Here,we develop a novel adhesive mechanism for governing wet adhesion and investigate the biological models of honeybee arolium for reproducing the natural wet adhesive systems.Micro-nano structures of honeybee arolium and arolium-prints were observed by Cryogenic scanning electron microscopy(Cryo-SEM),and the air pockets were found in the contact interface notably.Subsequently,the adhesive models with a three-phase composite interface(including air pockets,liquid secretion,and hexagonal frames of arolium),were formed to analyze the wet adhesion of honeybee arolium.The results of theoretical calculations and experiments indicated an enhanced adhesive mechanism of the honeybee by liquid self-sucking effects and air-embolism effects.Under these effects,normal and shear adhesion can be adjusted by controlling the proportion of liquid secretion and air pockets in the contact zone.Notably,the air-embolism effects contribute to the optimal coupling of smaller normal adhesion with greater shear adhesion,which is beneficial for the high stride frequency of honeybees.These works can provide a fresh perspective on the development of bio-inspired wet adhesive surfaces.

Design and Analysis of Biomimetic Nose Cone for Morphing of Aerospace Vehicle

Morphing capability is absolutely vital for aerospace vehicle to gain predominant functions of aerodynamics, mobility and flight control while piercing and re-entering the atmosphere. However, the challenge for existing aerospace vehicle remains to change its structure of nose cone agilely. This paper carries out a lot of observational experiments on honeybee＇s abdomen which enhances the flight characteristics of honeybee by adjusting its biomorphic shape. A morphing structure is adopted from honeybee＇s abdomen to improve both the axial scalability and bending properties of aerospace vehicle, which can lead to the super-maneuver flight performance. Combined with the methods of optimum design and topology, a new bionic morphing structure is proposed and applied to the design of morphing nose cone of aerospace vehicle. Furthermore, simulations are conducted to optimize the structural parameters of morphing nose cone. This concept design of biomimetic nose cone will provide an efficient way for aerospace vehicle to reduce the aerodynamic drag.

Drag Reduction in the Mouthpart of a Honeybee Facilitated by Galea Ridges for Nectar-Dipping Strategy

Some nectarivorous animals have evolved highly specialized tongues to gather nectar from flowers. Here we show that the Italian honeybee, Apis mellifera ligustica, uses the uniformly-distributed ridges on the internal wall of the mouthpart to reduce drag while drinking nectar. We discovered that the tip of the tongue is covered with bushy setae and resembles a brush, and the ridges are parallel distributed on the inner wall of the galeae. Using high-speed camera, we recorded the morphology of the mouthpart when dipping the sucrose water. Considering the ridges and the movement rule of the glossa, we proposed a model for analyzing the mechanism of drag reduction. Theoretical estimation of the friction coefficient with respect to the dipping frequency indicates that the erectable bushy hairs and the ridges can significantly reduce friction when a honeybee drinks nectar. Results show that dimensions of the ridges play a key role in reducing friction. It can be concluded that the ridges on the galeae of honeybee＇s mouthpart can reduce the friction coefficient by 86% compared with the case of the transverse distribution co- efficient S = 40. Finally, the capability of drag reduction in the mouthpart of honeybee may inspire a creative concept for de- signing efficient viscous micropumps.

The Honeybee＇s Protrusible Glossa is a Compliant Mechanism

Many biological structures can perform highly-dexterous actions by using dynamic surfaces. To deal with the contradictive demands of high feeding efficiency and low energy expenditure during nectar feeding, the glossal surface of a honeybee un- dergoes shape changes, in which glossal hairs erect together with segment elongation in a drinking cycle. In this paper, we extracted a transmission link embedded in the glossa from postmortem examination and found that the compliance of the in- tersegmental membranes provides more possibilities for this highly kinematic synchronicity. According to the morphing phe- nomena of honeybee＇s glossa, we proposed a compliant mechanism model to predict the deformation behavior of honeybee considering elastic properties of the glossal intersegmental membranes. The increase of membrane stiffness may improve the capacity of elastic potential energy transfer, but will still result in the increase of mass. An index is introduced to evaluate the contradiction for optimizing structural parameters. This work may arouse new prospects for conceptual design of mi- cro-mechanical systems equipped with bio-inspired compliant mechanisms.

Honeybees have Hydrophobic Wings that Enable Them to Fly through Fog and Dew

Honeybees have received public attention for their remarkable performance in low-altitude flying and their outstanding airborne hovering capability. However, minimal attention has been given to their capability to fly through the harshest climatic conditions. In this study, we used a high-speed camera and recorded an interesting phenomenon in which honeybees （Apis mellifera ligustica） flew effortlessly through mists or drizzling rain. To identify the mechanism behind honeybees flying through mists, the microstructure of their wings was examined via atomic force microscopy and scanning electron microscopy. Ex- perimental results showed that the surface of a honeybee wing was rough, with bristles distributed on both the dorsal and ventral sides. The measurement results of the contact angle proved that the surface of honeybee wings was hydrophobie. Furthermore, hydrophobic proteins, which contained at least one hydrophobic tetra-peptide （i.e., AAPA/V）, were obtained. The rugged sur- face and hydrophobic proteins caused the hydrophobicity of honeybee wings. These results identify the hydrophobic mechanism of honeybee wings, which will be useful in designing hydrophobic structures.

Operculum of a Water Snail is a Hydrodynamic Lubrication Sheet

Water snails developed a distinct appendage, the operculum, to better protect the body against predators. When the animal is active and crawling, part of the underside of the shell rests on the outer surface of the operculum. We observed the water snails （Pomacea canaliculata） spend -3 hours per day foraging, and the relative angular velocity between the shell and operculum can reach up to 10°·s^-1, which might inevitably lead to abrasion on the shell and operculum interface. However, by electron microscopy images, we found that the underside of the shell and outer surface of the operculum is not severely worn, which indicates that this animal might have a strategy to reduce wear. We discovered the superimposed rings distributed concentrically on the surface, which can generate micro-grooves for a hydrodynamic lubrication. We theoretically and experimentally revealed the mechanism of drag reduction combing the groove geometry and hydrodynamics. This textured operculum surface might provide a friction coefficient up to 0.012 as a stability-resilience, which protects the structure of the snail＇s shell and operculum. This mechanism might open up new paths for studies of micro-anti-wear structures used in liquid media.

The Morphology and Reciprocation Movement of Honeybee＇s Hairy Tongue for Nectar Uptake

A honeybee uses its brush-like tongue （glossa） to dip nectar and the setae densely distributed on it can increase the amount of trapped nectar observably. The glossa is often simplified as a cylinder covered by uniformly distributed and vertically erected setae during the drinking process, herein variations of the dimensions together with the erection angles of glossal setae are assumed to be negligible. In this paper, a dynamic model for the glossa retraction phase under the specific erection pattern of glossal setae is established, and the energy saving mechanism is extensively studied by comparing four types of erection pat- terns. Then the theoretically-optimal configuration, which satisfies the minimum energy consumption, is achieved from the dynamic model. Using the scanning electron microscope and a specially-designed high-speed camera system, we measure the dimensions of the glossal satae and capture dynamics of the hairy glossa in nectar feeding. It is proven that the erection angle of the glossal setae varies along the tongue axis, which shows a high concordance with our theoretically-optimal configuration. Compared with the hypothetical uniform distribution mode of glossal setae proposed by former researchers, we obtain a 16% increase in energy saving from actual erection pattern.

Experimental Verification on Steering Flight of Honeybee by Electrical Stimulation

The artificial locomotion control strategy is the fundamental technique to ensure the accomplishment of the preset assignments for cyborg insects.The existing research has recognized that the electrical stimulation applied to the optic lobes was an appropriate flight control strategy for small insedts represented by honeybee.This control technique has been confirmed to be effective for honeybee flight initiation and cessation.However,its regulation effect on steering locomotion has not been fully verified.Here,we investigated the steering control effect of honeybee by applying electrical stimulation signals with different duty cycles and frequencies on the unilateral optic lobes and screened the stimulus parameters with the highest response successful rate.Moreover,we confirmed the effectiveness of steering control by verifying the presence of rotation torque on tethered honeybees and the body orientation change of crawling honeybees.Our study will contribute some reliable parameter references to the motion control of cyborg honeybees.

Effects of Nectar Property on Compensated Dipping Behavior of Honey Bees with Damaged Tongues

In nature,bees with damaged tongues are adapted to have a feat in collecting nectariferous sources in a large spectrum of concentrations(19%-69%)or viscosities(10^(-3)Pa·s to 10^(-1)Pa·s);however,eff ects of nectar property on compensated dipping behavior remain elusive.Combining the bee tongue anatomy,high-speed videography,and mathematical models,we investigate responses of honey bees with damaged tongues to fluidic sources in various properties.We find that,bees with 80%damaged tongues are deprived of feeding capability and remarkably,the dipping frequency increases from 4.24 Hz to 5.08 Hz while ingesting 25%sugar water when the tongue loses 0-30%in length,while declines from 5.08 to 3.86 Hz in case of 30%damaged tongue when sucrose concentration increases from 25%to 45%.We employ the energetic compensation rate and energetic utilization rate to evaluate eff ectiveness of the compensation from the perspective of energetic regulation.The mathematical model indicates that the energetic compensation rate turns higher in bees with less damaged tongues for ingesting dilute sugar water,demonstrating its capability of functional compensation for combined factors.Also,the tongue-damaged bees achieve the highest energetic utilization rate when ingesting~30%sugar water.Beyond biology,the findings may shed lights on biomimetic materials and technologies that aim to compensate for geometrical degradations without regeneration.

Thermoregulation Capacity of Honeybee Abdomen for Adaptability to the Ambient Temperature

Honeybees are ectotherms that have the specific ability to control their body temperature to match environmental change. Honeybees, such as Apis mellifera L., can flex and extend their abdomen to transfer heat with the environment. Their folded intersegmental membranes which are distributed in the segments of their abdomen, play key roles in heat transfer with abdominal movements. In this study, a temperature-controlled device was established to simulate varying ambient temperature and the abdominal behaviors of honeybee were investigated. Experimental results show that the folded intersegmental membranes make a considerable difference on the bees＇ heat transfer ability. Bees can achieve temperature equilibrium by moving their abdomen, in this way bees increase convection to achieve temperature equilibrium. The higher the experimental temperature was, the faster the membrane moved and the shorter time required to reach heat balance. The function of folded intersegmental membranes on heat transfer was further elucidated by proposing a convective heat transfer model. The study on thermoregulation mechanism of honeybee abdomen helps explain its strong adaptability to the external environment as well as its defensive behavior against foreign invaders.

A Review of Energy Supply for Biomachine Hybrid Robots

Biomachine hybrid robots have been proposed for important scenarios,such as wilderness rescue,ecological monitoring,and hazardous area surveying.The energy supply unit used to power the control backpack carried by these robots determines their future development and practical application.Current energy supply devices for control backpacks are mainly chemical batteries.To achieve self-powered devices,researchers have developed solar energy,bioenergy,biothermal energy,and biovibration energy harvesters.This review provides an overview of research in the development of chemical batteries and self-powered devices for biomachine hybrid robots.Various batteries for different biocarriers and the entry points for the design of self-powered devices are outlined in detail.Finally,an overview of the future challenges and possible directions for the development of energy supply devices used to biomachine hybrid robots is provided.