【作者】 张占立；

【导师】 杨继昌； 丁建宁；

【作者基本信息】 江苏大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 随着科学技术和仿生学的发展,仿生学在工程技术和微纳米科学方面的应用越来越广泛,因此人们更加重视从宏观范围到微观范围内对生物材料的形貌特征、力学性能及摩擦学行为等方面的研究。蛇类爬行动物腹鳞表面具有微观非光滑特性和疏水特性,对蛇的运动起着重要作用,并具有不沾泥土、保持蛇体清洁的作用。腹鳞的这些生物学特性对解决不同尺度范围内的减粘降阻及摩擦各向异性问题具有启示作用。本文以缅甸蟒蛇、乌梢蛇和红点锦蛇三种蛇的腹鳞为研究对象,从材料成分、微观结构、表面性能、力学性能、宏观和微观摩擦学行为等方面进行研究,建立了腹鳞表面摩擦运动的接触模型,旨在了解并掌握腹鳞的材料特性和摩擦学行为,揭示腹鳞的摩擦机理,为蛇类爬行动物腹部表皮的仿生制造提供依据。本论文的主要工作及结论如下:用傅立叶红外光谱仪、分析天平、物性测试仪分别测试腹鳞的材料成分、吸湿性和拉伸力学性能。结果表明,三种腹鳞的材料成分基本相同,是α角蛋白与β角蛋白的复合结构。腹鳞材料具有吸湿性,吸湿率在8%左右。腹鳞干样品的拉伸弹性模量为1.5 GPa左右,断裂强度为80 MN/m~2左右,蟒蛇腹鳞的弹性模量最高,乌梢蛇的最低;湿样品的弹性模量是干样品的1/5～1/3,断裂强度是干样品的1/2左右。这项研究主要在于了解腹鳞的材料特性,为腹鳞材料的摩擦特性研究及其仿生制造提供基础资料。用扫描电镜和原子力显微镜观察腹鳞表面的微观形貌。结果表明,三种不同腹鳞表面的微观形貌具有相似的结构特征,即高度有序的阵列结构,该结构可以看作由微凸体、微孔、凹坑以及板结构部分周期排列而成,并可以用排间距等11个参数定量描述。不同腹鳞表面上的微观形貌也有很大差异,主要表现在:蟒蛇腹鳞表面上的微凸体为手指状,其高度为200 nm左右,而红点锦蛇和乌梢蛇的微凸体是三角形,高度为60 nm左右;蟒蛇腹鳞的微凸体具有很大的后向角度,呈现出一边锋利、一边平缓的高度非对称性棘爪结构,而红点锦蛇和乌梢蛇腹鳞表面微凸体的后向角度很小;蟒蛇腹鳞表面微凸体的密度最高,是另外两种的1.8倍;蟒蛇和红点锦蛇的板结构部分约占排间距的1/2,而乌梢蛇腹鳞表面上基本没有板结构部分;乌梢蛇和红点锦蛇腹鳞表面凹坑的深度和直径远大于微孔,而蟒蛇腹鳞的凹坑深度相对较小;红点锦蛇腹鳞表面的微孔直径、深度及密度最大。腹鳞表面相似的微观结构特征使其具有减粘降阻及摩擦各向异性的作用,其差异是不同蛇类为了更好地适应栖息环境及运动方式造成的,并与蛇种有关。用接触角测量仪测量腹鳞表面的水接触角。结果表明,蛇类爬行动物腹鳞表面属于疏水表面,缅甸蟒蛇腹鳞表面的水接触角平均值是110.6°,乌梢蛇的是105.8°,红点锦蛇的是104.5°;腹鳞材料吸湿后表面的水接触角下降2°～3°。腹鳞表面的微观形貌可以增加表面的疏水性;在微纳米范围内,接触角随表面微凸体密度的增大而增大,随微凸体高度的增加而增大。用纳米硬度计研究腹鳞材料的纳米力学性能。结果表明,蟒蛇和红点锦蛇腹鳞材料压入弹性模量的最大值分别为1310 MPa、920 MPa,纳米硬度的最大值分别为104 MPa、90 Mpa;蟒蛇腹鳞的力学性能均高于红点锦蛇;压入过程中,腹鳞材料有蠕变,表明了腹鳞材料的粘弹性属性。腹鳞材料的纳米力学性能与蛇的生活环境有关。用UMT-2摩擦磨损试验机研究腹鳞表面的宏观摩擦特性。结果表明,腹鳞表面与不锈钢球摩擦副之间具有很低的摩擦阻力,摩擦系数为0.05～0.13,其中蟒蛇的摩擦系数最小,与聚四氟乙烯的相当,红点锦蛇的最大;干摩擦及水润滑时,摩擦系数随载荷的增加而减小,随滑动速度的增加而增加;油润滑时,摩擦系数随载荷的增加而减小,随滑动速度的增加而减小;水润滑时的摩擦系数是干摩擦时的1.3～1.9倍,油润滑时的摩擦系数是干摩擦时的0.8～2.3倍;腹鳞表面有宏观摩擦各向异性行为,前向运动时的摩擦阻力最小,后向运动时的摩擦阻力最大,是前向运动时的1.3～1.5倍,侧向运动时的摩擦阻力介于两者之间,并接近后向运动时的摩擦阻力。腹鳞滑动时的摩擦阻力由表面间粘着力、犁沟力、微凸体的机械变形阻力以及弹性滞后阻力组成,表面粘着力引起的阻力是摩擦力的主要部分;腹鳞表面的疏水性,减小了表面能;微凸体可以破坏水膜的连续性,表面凹坑存储的蛇体分泌液,增加了表面的疏水性,这些是腹鳞表面具有减粘降阻、减少泥土粘附的原因;腹鳞表面微观结构的倾斜角度是造成摩擦各向异性的主要原因。用原子力显微镜的LFM模式研究腹鳞表面的纳米摩擦性能。结果表明,腹鳞表面具有较低的粘附力和表面粘附能,缅甸蟒蛇、红点锦蛇、乌梢蛇腹鳞表面的粘附能分别为0.042J/m~2、0.045 J/m~2和0.047J/m~2;腹鳞表面的平均粘附力随着表面粗糙度的增加而减小;腹鳞表面的微观摩擦力与表面的微观形貌及其斜率有关,摩擦力的波动周期与微凸体的变化周期相同,但与微凸体的高度关系不大,与微凸体表面的斜率关系密切,并与微凸体的斜率分布相同;在蟒蛇腹鳞表面微凸体的边缘处,探针上升时的摩擦力变化剧烈,是下降时的2倍多,表现出微观摩擦的各向异性。腹鳞表面的摩擦力随载荷的增加而线性增大,与速度无关;三种腹鳞中,蟒蛇腹鳞的摩擦系数最低,红点锦蛇和乌梢蛇的基本相等。低载荷时,表面粘附力引起的摩擦力占微观摩擦力的主要部分。蟒蛇腹鳞表面上周期性排列的高度非对称的棘爪状微凸体结构是微摩擦各向异性的主要原因。研究结果表明,改变腹鳞表面上微凸体的倾斜角度、分布方式及密度可以改变不同方向上的摩擦力大小。本文的研究结果表明,蛇类爬行动物腹鳞表面在宏观和微观范围内均具有减粘降阻和摩擦各向异性作用,腹鳞的材料特性和表面的微观形貌是其主要原因。更多还原

【Abstract】 With the development of science and technology,the bionics has been widely used in engineering and the research on biomaterial micrograph, mechanical properties and tribological behavior received great attention from micro area to macro one in the past few decades.The snakes’ ventral scale has the micro non-lubricity and hydrophobe properties.It plays a great role in the snake body movement and keeps the body away from the clay,maintains the body clean.All these biological properties give a hand to figure out the problem of how to decrease the conglutination,less the resistance and overcome friction anisotropies.This paper focuses on the ventral scale research on Burmese python、Zaocys dhumnades and Elaphe rufodoreata.The contact model of the ventral scale friction movement is founded on the work of material component analysis,microstructure, surface characteristic and micro & macro tribological behavior.It aim is to understand the ventral scale material characteristic and tribological behavior and to reveal the ventral scale friction mechanism so that the bionics fabrication on ventral scale can be made.Firstly,the ingredients of ventral scale are analyzed by Fourier transform Infrared spectrometer.The results indicate that spectrums of the three ventral scale are extremely similar and the main structure isα-helix keratin.Texture analyzer is used to test the tension mechanical character of the ventral scale material.It shows the elastic modulus of the ventral scale is about 1.5 GPa and the fission strength is lower than 90 MN/m~2.The material of ventral scale has moisture absorption ability,the rate of which is about 8%.The elastic modulus of the python’s ventral scale is the highest of all while that of the Zaocys dhumnades is the lowest.The elastic modulus of the damp sample is 1/5 to 1/3 of the dry one.All conclusions above all aim to know the material characteristic and to provide the basic resource of bio-fabrication.The topography of ventral scale surface is obtained with SEM and AFM.Regularly arrayed micro-structure is on the snake ventral scale surface.The structure is observed as a structure comprised of periodically arrayed micro-convex,micro-pits,micro-holes and plate-like part.Eleven parameters are used to depict the topography quantificationally.The micro-topography of ventral scale surface varies as species.The micro-convex on ventral scale surface of python is finger-like convex,and its height is 200 nm.The one of the Elaphe rufodoreata and Zaocys dhumnades is triangle and its height is 60 nm.This mciro-convexs is the claw-like structure with one side sharp and the other is flat.Its forward angle is small.The backward angle of the Elaphe rufodoreata and Zaocys dhumnades is small while the one of python is quite great.The density of micro convex on the ventral scale surface of python is the highest of all, which is as 1.8 times as that of the others.There is no plate-like structure on the ventral scale surface of Zaocys dhumnades,the plate-like structure of the Burmese python and Elaphe rufodoreata is 1/2 of the periodicity of terraces.The density of micro-pits on the ventral scale surface of Elaphe rufodoreata’s is high,and the one of Zaocys dhumnades is low.The depth and diameter of micro-holes on the ventral scale surface of Zaocys dhumnades and Elaphe rufodoreata are far bigger than their micro-pits.The similar microstructure of the ventral scale surface makes it have the role to decrease the conglutination,less the resistance.The difference of different kind’s snakes is to make them to adapt for the outer environment.The water contact angle of the ventral scale surface is measured by water contact angle tester.The result shows that the ventral scale surface snakes are hydrophobic.The mean water contacting angle of ventral scale surface of python,Zaocys dhumnades and Elaphe rufodoreata is 110.6°, 105.8°and 104.5°,respectively.The water contacting angle decreases by 2°to 3°after wetted.The increase of the density and the height of micro convex on the ventral scale surface will enlarge the water contacting angle.The nano mechanical properties of the ventral scale material are researched by using nanoindentation.The result shows that the elastic moduli for ventral scale of the Burmese python and Elaphe rufodoreata are 1310 MPa and 920 MPa,respectively and the nano-hardness are 104 MPa and 90 Mpa,respectively.The mechanical properties of the python’s ventral scale are higher than the one of Elaphe rufodoreata.Creep deformation in the ventral scale material occurs during the process of impressing.UMT-2 model of universal micro materials tester is used to research the macro friction properties of the ventral scale surfaces.It is found the friction resistance between ventral scale surface and steel ball is low,and the coefficient is 0.05 to 0.13.The friction coefficient of python’s sample is the lowest of all,which is equal to the one of the PTFE,and the one of the Elaphe rufodoreata is the biggest of all.Under dry friction and water lubrication,the friction coefficient decreases as the load or sliding velocity increases.Under oil lubrication condition,the friction coefficient decreases with the increase of the load and the sliding velocity.The friction coefficient under water lubrication is 1.3 to 1.9 times of that under dry friction.And the friction coefficient under oil lubrication is 0.8 to 2.3 times of that under dry friction.The friction force for the ventral scale surface is anisotropic.The forward motion friction resistance is the lowest of all and the backward one is the biggest.The friction resistance in the lateral motion is between the two above,which is nearly equal to the backward one.The friction resistance in backward motion is 1.3 to 1.5 times of that in the forward motion.The lean angle of the micro convex on the ventral scale surface is the main cause of the friction anisotropy.The friction resistance of sliding motion is composed of the resistance due to the adhesion force on the surface,plough force,the mechanical distortion resistance of the micro-convex and elastic resistance,and among them the adhesion force is the main one.The hydrophobia of the ventral scale surface decreases the surface energy.The micro-convex can destroy the continuous water film. The micro-hole on the surface stores the snake’s secretion,increasing the surface’s hydrophobia.And these are the reasons for decreasing adhesion force and soil’s adhesion force function of snake ventral scale surface.The slope angle of microstructure in the ventral scale surface is the main cause of anisotropic friction properties.The nano friction properties of ventral scale surface are researched by using LFM mode of AFM.As a result,the adhesion force and surface energy for ventral scale surface of snake is low.The adhesion energies for ventral scale surface of Burmese python,Elaphe rufodoreata and Zaocys dhumnades are 0.042 J/m~2,0.045 J/m~2 and 0.047 J/m~2,respectively.The mean adhesion force of ventral scale surface decreases as the surface roughness increases.The friction force of ventral scale surface is related to topography and slope of the micro-convex.The periodicity of the friction variation is the same as the one of the micro-convex.It is not related to the height of the micro-convex,but is highly related to the slope of the micro-convex surface,which is the same as the distribution of the micro-convex.At the brink of the micro-convex on ventral scale surface of python,the friction force vary greatly when the tip is ascending phase,and the varying range is twice the one when the tip is drop phase.The friction force of the ventral scale surface linearly increases as the load increases, but not related to the velocity.During the low load,due to the surface adhesion,the micro friction becomes the main factor of the friction.The friction coefficient for the ventral scale of python is the lowest of all,which is basically the same as the one of Elaphe rufodoreata and Zaocys dhumnades.更多还原