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聚合物-异质材料界面微纳尺度力学行为的分子动力学模拟研究
Alternative TitleMolecular dynamics simulation of mechanical behavior of polymer/substrate interface at micro-/nano-scale
孟昶宇
Thesis Advisor廖丽涓
2019-05-27
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype硕士
Degree Discipline工程力学
Keyword聚合物-异质材料界面 微观力学行为 分子动力学模拟 粗粒化 微结构演化
Abstract

  聚合物-异质材料界面广泛存在于如聚合物基复合材料及粘接联结结构等体系中,其动力学行为直接决定系统的稳定性和可靠性。界面相的存在使得多相系统表现出异于各单一相的物理力学性质,其失效行为由聚合物本征物理性质、外部载荷及约束效应共同决定。本研究关注聚合物及其界面体系在微纳尺度下的力学行为,采用分子动力学模拟手段捕捉了聚合物-异质材料界面在拉伸条件下的失效演化过程,发展了聚合物的粗化粒子模拟方法,获得了微观相特性对界面力学行为的影响规律。本研究主要包括以下内容:

  1)建立了约束条件下聚合物-异质材料界面微结构参量演化与失效过程之间的对应关系;发展了一种界面体系稳定性和能量状态的预示方法,并确定了二面角分布状态对界面失效的决定性作用,进而给出应力应变曲线以及体系能量演化特征点的机理性解释。

  2)发现了约束条件下聚合物-异质材料界面的屈服强度具有聚合物层厚度依赖性,提出了描述聚合物分子链搭桥和缠结效应的表征参量,发现界面强度的厚度依赖性由搭桥效应所主导;界面屈服强度随加载率呈现分段单调变化;提出了一种描述失效模式的参数,并在一定范围内给出了界面失效模式关于聚合物层厚和加载率的图谱,并发现界面失效模式由加载率主控。

  3)发展了一种描述嵌段共聚物的粗粒化势函数,模拟了其块体材料的相分离行为,复现了内部硬段的“条带状”聚集构型;基于嵌段共聚物和异质材料两相界面体系力学行为的全原子模拟结果,获得了由聚合物内部硬段聚集导致的完全失效应变的加载率依赖性,并给出了其微结构解释。

Other Abstract

  Polymer/substrate interface is widely used in systems such as polymer matrix composites and adhesive bonded joint structures. Its dynamic behavior directly determines the stability and reliability of the system. Due to the presence of the interfacial phase, the physical and mechanical properties of the multiphase system are different from that of each single phase. The failure behavior of interface is determined by the intrinsic physical properties of the polymer, external loads and constrained effects simultaneously. The present study focuses on the mechanical behavior of polymers and the relating interface at micro-/nano-scale. Molecular dynamics simulation was used to capture the failure evolution process of polymer/substrate interface under tensile loading conditions. The coarse-grained molecular simulation method of polymer systems was developed and the influence of microscopic phases on the mechanical behavior of the interface was obtained. The main works of this paper are as followed.

  (1) The correlation between the evolution of the microstructure parameters and the critical moments of the failure behavior during the loading process of the constrained polymer/substrate interface was established. A prediction method of the instability and energy state of the interfacial system was developed. The dihedral distribution governs the interfacial failure behavior largely. The rational mechanism explanation of the feature points of the stress-strain curve and the system energy evolution was given.

  (2) The thickness-dependence of yield strength of the constrained polymer/substrate interface was illustrated. The characterization parameters used to describe the bridging and entanglement effects of polymer molecular chains were also proposed. It was concluded that the thickness dependence of the interfacial strength is dominated by the bridging effect. The non-monotonic relation between the yield strength and the loading rate was observed. In addition, a parameter describing failure mode was introduced. Accordingly, a phase diagram of failure mode with respect to polymer layer thickness and loading rate was provided within a given range. It showed that the failure mode is mainly controlled by loading rate.

  (3) A coarse-grained potential function was developed to describe the physical behavior of block copolymers. The phase separation phenomenon of block copolymers was reproduced with the "strip" aggregate structure of hard segments. The loading rate dependence of the total failure strain due to the aggregation of hard segments was obtained by all-atom simulation. The microstructural interpretationwas given to explain the rate dependence phenomenon.

Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/79103
Collection流固耦合系统力学重点实验室
中国科学院力学研究所
Recommended Citation
GB/T 7714
孟昶宇. 聚合物-异质材料界面微纳尺度力学行为的分子动力学模拟研究[D]. 北京. 中国科学院大学,2019.
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