微纳尺度下生物分层结构的力学性能表征及行为研究

发布时间：2018-04-16 13:35

本文选题：生物分层结构 + 牙釉质　；参考：《华东理工大学》2014年博士论文

【摘要】：分层结构广泛存在于牙齿、骨骼等生物材料和结构中,表现为优异的机械与力学性能。对其宏/微观结构-性能-功能之间关系的深入理解和认识,不仅使人们更好地认识生物材料和结构的进化规律,而且有助于设计、制造出拥有更佳性能的仿生结构和器件,相关研究一直是机械、材料、力学和医学领域共同关注的热点。本文以典型天然生物分层结构材料-牙釉质层(牙齿最外层材料)为实验研究对象,利用微纳米压/划痕实验、有限元模拟和理论分析等方法,系统研究了其微观摩擦磨损机理、微观力学性能表征以及循环接触行为。主要的研究工作和结论如下： (1)纳米尺度下牙釉质的各向异性摩擦行为。采用球锥形压头的纳米压痕仪,进行了不同载荷下釉质层在单个釉柱层级的咬合面和轴剖面上原位划痕实验,基于表面粗糙度、划痕深度和残余深度,分析了划痕过程中的弹性回复和非弹性变形行为。结果表明：釉柱咬合面上的弹性回复和非弹性变形明显小于轴剖面,且咬合面更加耐磨损。纳米尺度上牙釉质的摩擦系数表现为载荷相关性与位置相关性,摩擦系数的载荷相关性源于划痕过程中的犁沟效应,而位置相关性是由于正向加载、划痕方向与细长状羟磷灰石晶粒方向的夹角差异导致。 (2)圆柱/包围层微结构单元压痕力学分析。考虑到富蛋白质的釉柱鞘对硬质的釉柱压痕可能产生的影响,建立了圆柱/包围层结构的理论模型,得到了压痕载荷-位移关系的弹性理论解,结合有限元讨论了包围层的厚度和圆柱/包围层的弹性模量对压痕曲线的影响；此外,讨论了仪器化压痕测试圆柱/包围层结构弹性模量时所采用的Oliver-Pharr方法的局限性,提出了门槛压入深度参数,当压痕深度小于该门槛值时,测试模量的误差在±10%内。研究表明：对于可压缩弹性包围层,产生相同的压痕位移所需的载荷会随着模量的增加而降低；而不可压缩层对圆柱的弹性压痕响应影响不明显。另外,门槛压入深度与模量、包围层厚度和圆柱半径比密切相关,该结果对如何使用Oliver-Pharr方法测试类似釉柱/釉柱鞘结构的弹性模量有指导意义。 (3)微、纳尺度下牙釉质循环压痕行为的各向异性分析。利用Berkovich压头在釉质和釉柱两个层级上分别进行循环压痕实验,基于压痕位移曲线,分析了循环压痕过程中的变形行为和能量耗散。研究发现：压头在循环载荷作用下会连续压入材料,深度变化经历瞬态并达到准稳态。在准稳态时,每周压入深度和每周塑性能耗散与最大压痕载荷无关,但与循环载荷幅值成正比,并且轴剖面的压痕深度幅值和每周压入深度要大于咬合面。进一步提出,利用釉柱上的单循环和多循环载荷-位移曲线之间的偏差来描述咬合面和轴剖面的循环响应差异,发现在咬合面上,晶粒和蛋白质的界面剥离以及蛋白质分子循环过程中的不完全折叠是其疲劳损伤的主要原因,而在轴剖面上,除了与咬合面相同的损伤形式外,细长状晶粒因弯曲发生的断裂以及晶粒末端剥离对失效有影响。 (4)循环压痕作用下牙釉质变形模拟分析的双层结构模型。基于微纳尺度下内、外层釉质不同的釉柱排列形式,提出了循环压痕有限元分析的双层结构模型,以模拟其结构重复接触的问题。研究结果表明,外层釉质因其更大地抵抗接触变形的能力,承担了主要载荷,循环过程中的内层釉质上产生更大的等效塑性应变和较低的应力,内层釉质拥有更好的抵抗断裂的能力。 (5)生物/仿生材料广义错列结构的热-机应力分析。基于牙釉质结构的微观分析,提出表征承载生物分层结构材料的错列微观结构,通过修正经典的“剪滞模型”,从应力解和位移解的角度分别讨论结构在热-机载荷作用下的应力分布和等效热膨胀系数。与有限元计算结果对比表明：应力模型能更好地预测应力分布；当硬组织小板的纵横比和体积分数超过临界值时,结构的等效热膨胀系数会达到常数；两个理论模型的相对误差会随着两个小板错列程度的增加而增加。
[Abstract]:In this paper , we study the micro - friction wear mechanism , micro - mechanical property characterization and cyclic contact behavior of typical natural biological layered structure material - dental enamel layer ( the outermost layer of tooth ) . The main research work and conclusion are as follows :

The results show that the elastic recovery and inelastic deformation of the enamel layer on the occlusal surface of the enamel column are obviously smaller than those of the axial section and the occlusal surface is more wear - resistant . The results show that the elastic and inelastic deformation of the enamel on the occlusal surface of the enamel is obviously smaller than that of the axial section , and the occlusal surface is more resistant to wear . The friction coefficient is caused by the plow groove effect in the scratch process , and the positional correlation is caused by the difference of the forward loading , the scratch direction and the direction of the elongated hydroxyapatite grain .

( 2 ) The indentation mechanical analysis of the microstructure unit of the cylindrical / surrounding layer . The theoretical model of the structure of the cylinder / surrounding layer is established in consideration of the possible influence of the rich protein glaze sheath on the indentation of the hard glaze column , and the elastic theoretical solution of the indentation load - displacement relationship is obtained . The influence of the thickness of the surrounding layer and the elastic modulus of the cylindrical / surrounding layer on the indentation curve is discussed in combination with the finite element method .
In addition , the limitation of the Oliver - Pharr method used in the testing of the elastic modulus of the cylindrical / surrounding layer of the instrumented indentation is discussed , and the threshold pressure - in depth parameter is proposed . When the indentation depth is less than the threshold value , the error of the test modulus is within 卤 10 % . The study shows that the load required for generating the same indentation displacement for the compressible elastic surrounding layer decreases with the increase of modulus ;
In addition , the threshold press - in depth is closely related to the modulus , the thickness of the surrounding layer and the ratio of the radius of the cylinder . The results are of great significance to how to use the Oliver - Pharr method to test the elastic modulus of the similar glaze / enamel structure .

The deformation behavior and energy dissipation in the process of cyclic indentation are analyzed by using the results of cyclic indentation experiments at two levels of enamel and glaze . The results show that the interfacial peeling of grains and proteins and incomplete folding in the process of molecular cycling are the main causes of fatigue damage .

( 4 ) The double - layer structure model of the simulated analysis of the tooth enamel deformation under the action of cyclic indentation is presented . The double - layer structure model of cyclic indentation finite element analysis is proposed based on the different patterns of enamel columns in the inner and outer layers of the micro - nano - scale . The results show that the outer enamel has higher equivalent plastic strain and lower stress on the inner enamel due to its greater resistance to contact deformation , and the inner enamel has better resistance to fracture .

( 5 ) The thermal - mechanical stress analysis of the generalized staggered structure of biological / bionic material . Based on the microscopic analysis of the tooth enamel structure , the stress distribution and the equivalent thermal expansion coefficient of the structure under the action of heat - machine load are discussed from the angles of the stress solution and displacement solution based on the microscopic analysis of the tooth enamel structure .
When the aspect ratio and the volume fraction of the hard tissue panel exceed the critical value , the equivalent thermal expansion coefficient of the structure can reach constant ;
The relative error of the two theoretical models increases with the increase of the error of the two small plates .

【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TH117.1;TB302

【参考文献】