【作者】 李寅峰；

【导师】 李中华；

【作者基本信息】 上海交通大学 ， 固体力学， 2014， 博士

【摘要】 本论文关注了金属系统和生物系统中夹杂与界面的若干力学问题，针对两类系统中研究对象的特点，分别采用连续介质力学理论和分子动力学方法开展了一系列有意义的研究。金属材料中夹杂、界面、位错是影响材料宏观变形及微观失效机制的最重要因素，历来是固体力学和材料科学共同关注的研究热点。本文利用连续介质力学方法针对金属系统中的夹杂和界面问题进行研究，取得了以下重要进展：（1）基于弹性理论和Eshelby夹杂理论导出了应力梯度作用下，椭圆夹杂（包括空洞）由界面扩散控制的漂移速度的严密的理论解。该理论解所描述的夹杂迁移规律，可解释梯度应力中（如裂尖应力场）夹杂偏聚及相关的失效现象。（2）建立了位错与任意形状、任意性质非均质体（夹杂）相互作用的近似连续介质力学理论，运用该理论可获得位错与空穴、压力汽泡、剪切带及局部塑性变形区的相互作用力的近似理论解。该理论突破经典位错理论仅局限于处理位错与弹性夹杂相互作用的问题，而对弹性夹杂问题与经典解一致，因此是统一的连续介质理论。（3）分别获得金属基单向纤维增強、颗粒增強复合材料由界面扩散而引起的蠕变率及应力松驰的近似理论解，并讨论了单轴和双轴载荷条件的影响。该解为分析金属基复合材料在高温条件下强度损失、应力稳定性及界面滑移现象提供了理论分析依据。（4）获得金属多晶薄膜由界面扩散、表面扩散及晶界热蚀沟联合控制的蠕变率及应力松弛的理论解，发现具有粗粒化结构、低表面扩散率、高的表面自由能的薄膜有更高的抵抗蠕变能力及应力稳定性。该理论解为多晶薄膜材料的微结构设计、表面改性提供了理论指导。（5）建立了电场作用下的相场法数值分析模型，揭示了微电子器件的薄膜导线中夹杂的形态、电导系数、界面扩散各向异性等对夹杂的迁移与形态演变的影响规律。随着纳米科技的兴起和学科间交叉融合，纳米材料在生物系统的应用激发了广泛的关注，并在生物靶向、药物输运、免疫分析以及增强生物成像等领域展现出传统颗粒或蛋白质无法企及的优势。探索纳米材料与细胞界面交互作用的生物力学行为，对纳米材料的生物安全性控制和多功能化设计具有重要意义，是纳米生物力学的前沿热点课题。然而，连续介质力学方法不适用于该前沿问题的研究。本文基于分子动力学方法模拟了纳米材料穿透细胞膜进入细胞的动态过程，通过热力学积分方法与分子动力学方法的融合，计算了穿膜过程中体系自由能的变化，获得了以下学术成果：（1）利用耗散分子动力学的方法研究了四种表面改性的纳米颗粒穿透细胞膜能力，通过热力学积分方法计算了纳米颗粒进入细胞膜内部过程伴随的自由能变化，发现纳米颗粒表面上配体的物理排布能够显著影响颗粒穿膜进入细胞的模式，不仅合理地解释了生物学中令人困惑已久的实验现象，也为提高纳米颗粒的生物靶向、药物输运能力进行表面修饰控制的分子设计提供了依据。（2）结合粗粒化和全原子多尺度的分子动力学模拟以及活体细胞实验的成像观察，研究了石墨烯与细胞膜接触时的相互作用机理，首次揭示了石墨烯片可以通过尖角部位或者边缘上的凸起自发穿透细胞膜的穿膜模式。穿透过程会从局部穿透的部位沿着石墨烯边界进一步扩展。尺寸很小的石墨烯纳米片会在布朗运动和熵驱动力作用下调整到一个尖角垂直与细胞膜的方位，然后发生自发的尖角穿透。（3）选取了四种石墨烯的新型同素异构体，利用分子动力学方法模拟了对应的氢化结构，评估了0到100%范围内的氢化程度所对应结构的杨氏模量和固有强度[1]。结果表明，石墨烯同素异构体的力学性能随着氢化率的增加而逐渐退化，并对氢化表现出不同的敏感度。氢化反应使其力学性能衰退的规律和机理，为石墨烯同素异构体在超导、电子、能源以及光电等领域的潜在应用提供了分析依据。本论文的研究进展丰富并深化了近代连续介质力学有关夹杂和界面的理论体系，并通过学科交叉模式突破了连续介质力学的理论框架，拓展了固体力学在纳米生物这一前沿热点研究中的应用。更多还原

【Abstract】 This thesis deals with the mechanics of inclusions and interfaces in metallic andbiological systems. Based on the nature of the studied subjects, the continuum theory andmolecule dynamics method are employed for these two systems respectively, and a seriesof new models, solutions and observations is drawn.The inclusions, interfaces and dislocations in metallic materials are key factorsinfluencing their deformation behavior and failure mechanisms, and they have beenacknowledged as the main focus in the long term research of Solid Mechanics andMaterials Science. Based on the theory of Continuum Mechanics, this thesis hasaccomplished the following important contributions:(1) Based on the theory of Plasticityand Eshelby inclusion theory, an explicit expression is derived for motion velocity of anelliptical inclusion defect (including void defect) in isotropic matrix driven by interfacediffusion under gradient stress field, and it reveals the physical mechanisms ofexperimental observations, such as inclusion aggregation at crack tip and related failurephenomenon.(2) An approximate continuum theory is developed for the interactionbetween dislocations and inhomogeneity of any shape and properties. The proposedcontinuum theory is applicable to a variety of inhomogeneities, such as pore, gas bubble,shear band and plastically deformed zone. Compared to the existing theories which arelimited to the elastic inhomogeneities, the developed theory is one of general continuumtheory that can effectively handle the problems of elastic inhomogeneities as well asnon-elastic inhomogeneities.(3) Approximate analytical solutions are derived for creep rate and stress relaxation induced by interface diffusion in fiber-reinforced andparticle-reinforced metal matrix composites. The effects of the uniaxial and biaxial loadingconditions are compared. The results provide theoretical bases for the strength loss, stressstability and interface slip of Metal Matrix Composites under high temperature.(4) Ananalytical solution that interprets the effects of grain surface and interface diffusion as wellas grain boundary grooving on the creep rate in free-standing polycrystalline thin metalfilms is presented. The results reveal that films with coarse-grained structure, low surfacediffusivity and high surface free energy have high creep resistance and stress stability, andthey provide guidance for the microstructure design and surface characterization ofpolycrystalline thin metal films. And (5) A phase field model is established formorphological evolution of inclusion in interconnects under electric field. The effects ofinclusion shape, conductivity as well as anisotropic inclusion interface are illustrated.With the rise of nanotechnology and the advances in interdisciplinary research,nanomaterials have received intense global interest due to their potential biomedicalapplications. Taking advantage of the unique size-dependent properties over traditionaldyes and proteins, nanomaterials have shown great potential applications in the areas ofspecific targeting, drug delivery, and enhanced bioimaging. The investigation about theinteraction between nanomaterials and cell is critical to safe design and functionalization ofnanomaterial-enabled biomedical materials, which is the cutting-edge project in the currentresearch of biomechanics. However, such novel materials cannot be effectively addressedby the theory of continuum mechanics. This thesis thus investigates the penetration ofnanomaterials across a cell membrane using molecular dynamics simulations andcalculates the accompanied free energy evolution of the biological system bythermodynamic integration method. The following progresses are achieved:(1) Thedissipative particle dynamics simulations are performed to analyze the evolution of freeenergy as the ligand-coated nanoparticles (NPs) pierce through a lipid bilayer. Fourcharacteristic ligand patterns are considered, and their penetration modes are found to be strongly influenced by the ligand pattern on the nanoparticle surface. The results reveal thephysical mechanism behind an intriguing experimental phenomenon, and they provideuseful guidelines for the molecular design of patterned NPs for controllable cellpenetrability.(2) The interactions of graphene microsheets with cell membrane areinvestigated by combining coarse-grained molecular dynamics (MD), all-atom MD,analytical modeling, confocal fluorescence imaging, and electron microscopic imaging.The entry mode for graphene is proposed for the first time that the penetration initiates atcorners or asperities. Local piercing by these sharp protrusions initiates the membranepropagation along the extended graphene edge. For a small graphene flake, the Brownianmotion and entropic driving forces in the near-membrane region first position the flakeorthogonal to the bilayer plane, leading to spontaneous corner piercing.(3) Moleculardynamics simulations are performed to investigate the mechanical properties of hydrogenfunctionalized graphene allotropes (GAs) for H-coverage spanning the entire range(0-100%). Four allotropes with larger unit lattice size than graphene are considered. Themechanical properties of the hydrogenated GAs are found to deteriorate drastically withincreasing H-coverage within the sensitive threshold, beyond which the mechanicalproperties remain insensitive to the increase in H-coverage. The above research outcomesprovide insights for the potential application of graphene allotropes in the areas ofsuperconducting, electronics, energy, and photoelectrics.In summary, the outcomes of this thesis enrich and advance the continuum theory onthe mechanics of inclusions and interfaces. The interdisciplinary researches of the thesisadvance the framework of traditional continuum mechanics and promote the developmentof Solid Mechanics in the challenging research topics of Nano-Bio science.更多还原