Typical Bio-tribological Structures And Their Biomimetic Applications

Many living creatures have capability to adhere to substrates through contact and can control their contacting behavior. Such animals as house mouse and long-horned grasshopper Gampsocleis gratiosa combined their biomaterial rigidity and structure flexibility perfectly and have a strong adhesion ability to the contact surfaces of their organ to substrates. Friction and adhesion are the important tribological phenomenon occurring in biology, which become the technical for many engineering problems. To learn from nature and to convert the advantage structures of the living creature to the engineering structures will push the development of science and engineering.There are two kinds of the main adhere structures in the organ of living creature for locomotion. Surface contact and adhesion are the main function characteristic of the foot pad. The part consisting of some foot pad can insert into the rough structure of the substrates and the hook organ of some animals can directly insert into such substrate as earth for locomotion or cut. The hook has widely universality in living creature, such as, some plant, many large mammals and many insects. Many living creatures grow the organs with hook-like structures. The hook-like structure possesses strong adhesion ability to the rough solid surfaces. There are, in general, main three kinds of hook-like structures of the living creatures according to their structure characters and the function behavior: tractive hooks, static hooks and scoop hooks.Animal foot pads contacting soil can disperse the load acted on their bottom, reduce impact effects and enhance the adhesive strength during locomotion. It can be found from the analysis of animal operation that a increased hardness of soil will make the ground react impact enlarge while the animal foot fall onto it. Nevertheless, the soft and flexibile muscle tendon system of the foot pads can reduce effective rigidity of foot-soil system and the impact force of fall onto the ground.It was shown that the touch of the the foot pads of animal with a hard ground surface display a rolling phenomenon on soil ground surface, making the the foot pad adhere ability reduced considerably. One of the important functions of the foot pads is that the force acted on the soft soil is dispersed.The tribological behavior in the jump process locust was analyzed and the tribolical functions were investigated. Two model of friction put forward. The relation of the locust and varied substrates was realized. It was found that the locust utilized the adhere of the tarsal ends to substrates to drive its body for jumping up. The rotationally driving operation would enhance driving efficiency, depress characteristic demands for structure and material of the locust legs.The micro morphologies of Gampsocleis gratiosa foot pads and substrate surfaces (glass and calcium carbonate sprays wall) were examined by scanning electron microscopy (SEM), atomic force microscopy (AFM) and stereoscopy. The adhesive behavior at interface between the Gampsocleis gratiosa foot pads and glass surface tested in laboratory. It was found from the tests that the foot pads surfaces of Gampsocleis gratiosa are smooth in micro scale; the foot pads surfaces of Gampsocleis gratiosa have many approximate hexagon construction units with a scale of 3-7μm in macroscale, the units are partitioned by grooves and there are soft and flexible material inside the foot pad and the hairs growing on the pad cuticles. The Gampsocleis gratiosa cannot adhere to the vertical wall with calcium carbonate coating, but it can adhere firmly to vertical flat glass surface and CD disk surface and crawl freely in any directions (including upside down). The AFM analysis showed that the macroscopic smooth glass surface has a rough structure with sharper asperities in micro scale. The wall coated with calcium carbonate is, in fact, covered with a layer of calcium carbonate powder, and a size of the flaky powder is bigger than that of the hexagon construction units of Gampsocleis gratiosa foot pad. The CD disk surface has band-like bulges with a height less 200 nm. It is shown from the above results that the substrate surface morphologies have an important impact on the adhesion functions and properties of Gampsocleis gratiosa.The experimental results of several groups Gampsocleis gratiosa in adhesion showed that Gampsocleis gratiosa foot pad has a large adhesive strength and frictions on the glass surface. It was concluded by tests that the average static friction of Gampsocleis gratiosa foot pad on vertical flat glass surface is 6.04 times of normal adhesive strength between them. The adhesion experiments showed that the foot pads of Gampsocleis gratiosa have effectively adhering ability on clean horizontal glass and the maximum coefficient of friction reached 14.59 and minimum coefficient of friction was above 4.5. The dynamic friction tests were run on a universal tribology tester (CETR Ltd.). The friction tests were conducted using specimens of the foot pads of Gampsocleis gratiosa in vitro. It was demonstrated that the dynamic friction coefficient of the foot pad of Gampsocleis gratiosa is very low. The maximum static friction coefficient was higher 100 times than the dynamic friction coefficient.The tribological behavior of the foot pads of Gampsocleis gratiosa on a horizontal glass surface in the conditions of existing a water film and micro soil particles, respectively. The results showed that the middle medium (water film and micro soil particles) at the contacting interfaces influence the adhesion and friction considerably. Compared with the clean glass substrate surface, the friction force is lower by 8%-28% in the condition with the middle medium at the contacting interfaces.The physical contact models of the foot pads of Gampsocleis gratiosa holding on vertical glass surface and the vertical calcium carbonate coating surface were established. The micro rough structure units of the Gampsocleis gratiosa foot pad surface and the glass surface are easy to insert each other. This makes the Gampsocleis gratiosa foot pad structure units hold the asperities of the glass surface and, as a result, the static friction and adhesion should be increased due to this mechanism.Biomimetic design model of the subsoiler structure of agricultural machinery established learning from a house mouse claw configuration feature. The biomimetic design of the components for squeezing bore without digging for underground bore were carried out learning from such soil-borrowing animal as earthworm. The soil-borrowing animals have multi-function behavior to reduce resistance against soil to earth when they move in soil, including hydrophobic surface materials, geometrical morphology, micro eletro-osmosis and cuticle flexibility of their body surface. These structures can be converted to work parts structure with analogical function through biomimetic method. Learning from the geometrical configurations and morphologies of soil-borrowing animals, we designed and processed 6 squeezing heads with biomimetic structure used for tests. The results showed that squeezing heads with biomimetic geometrical configuration can reduce the contact area with soil due to the partitioning action to the contact interface between the squeezing heads and soil. This partitioning action can breakdown the interface continuous water film compared with conventional (smooth) squeezing heads. So the interface adhesion strength was lowered considerably. Based on the contact relation between the biomimetic squeeze head and soil, a contact model of the biomimetic annular surface squeezing head with soil was established. It was found that the biomimetic annular surface possessed lower working resistance against soil and the lengthways concave type squeeze heads possessed effective resistance reduction property, demonstrating a reduced working resistance by 17% compared with the conventional head.