热-力耦合作用下碳纤维增强热塑性复合材料的大变形宏/细观力学研究

Carbon fiber reinforced thermoplastic polymeric composites can go through melting/freezing repeatedly that makes them reshaped and recyclable. Therefore, they are commonly regarded as green materials that will undoubtedly replace thermosetting counterparts in the near future. In additional, thermoplastic composites are capable of deforming largely, which are attractive in many important domains and act as the best choice for the materials to fabricate special compositions, e.g. composite gun tube, artificial vessels and artificial skin, etc. Finite strain deformation of such composites with thermo-mechanical coupling effects is highly nonlinear, which is too complicated to clearly understand so far, and thus becomes the main obstacle in preventing the breakthrough of them into a broad field of applications. This project is to study nonlinear thermo-mechanical behaviors and corresponding micro-mechanisms for such composites by the use of theoretical, experimental and FEM investigations. The main objectives are i) to interpret the synergism effect between reinforcements and polymer molecular chains from a molecule conformation transition point of view, and ii) to quantitatively determine the relationship between macro/micro-mechanical behaviors and microstructures. Based on molecular chain network model, micromechanics theory shall be adopted to unify the constitutive equations for thermoplastic polymers at different temperature levels relative to glass transition temperature Tg. Anisotropic finite strain elasticity and Simo's additive-splitting method are untilized to construct an analytical model for the visco-elastic-plastic-damage behaviors of fiber reinforced thermoplastic composites. The project will be helpful to gain the deep understanding nonlinear finite strain deformation of such composites subjected to thermal, mechanical and combined loading. The final achievements are given in terms of robust theoretical models, efficient numerical codes and reliable experimental techniques, which are adopted in the designing, processing and application of such composites.

碳纤维增强热塑性复合材料具有可降解和易成型等独特性能，成为复合材料未来发展的主要方向。由于变形能力很大，所以该类复合材料在许多重要领域具有诱人的应用前景。热-力耦合作用下该类复合材料的变形呈现高度非线性，国内外相关研究都处于起步阶段。由于还不清楚变形机制，极大地阻碍了它们的广泛应用。本项目采用试验、理论和数值模拟相结合的方法解析非线性大变形及其微观机理。从分子构型演化出发，揭示增强体和聚合物分子链在变形过程中的协同效应，建立宏/细观力学性能和微结构参数之间的定量关系。基于分子链网络模型,运用细观力学方法建立热塑性聚合物在不同温度下的统一本构关系。运用各向异性大变形弹性理论和Simo的叠加原理建立热塑性复合材料的粘弹性-塑性-损伤力学模型和计算方法。本项目研究将促进碳纤维增强热塑性复合材料大变形力学行为的深入理解，为该类复合材料的优化设计、制备和应用提供可靠的理论模型、数值方法和试验技术。

项目“碳纤维增强热塑性复合材料的热-力耦合大变形力学研究” 旨在建立橡胶态和玻璃态聚合物的大变形本构理论；建立热-力耦合作用下碳纤维增强热塑性复合材料的大变形本构关系；通过破坏试验和数值模拟揭示损伤竞争机制，建立该类复合材料的粘弹性-塑性-损伤力学模型。经过3年的共同努力，项目组成员对于如下几个问题获得了非常好的研究成果。（1）基于Eshelby的等效夹杂理论建立了热塑性复合材料的大变形等效均匀化理论。该理论具有清晰的物理含义，精确度高。相对于现有其他模型，准确度最高，可以解释微结构的变形机制；（2）建立了热塑性复合材料的Eshelby大变形表达式，并合理预测了其有限变形机理和大变形应力-应变关系。同时利用分子链网络模型在分子尺度上揭示了该类复合材料的硬相-软相之间的协同效应；（3）基于Abaqus应用程序，调试成功玻璃态聚合物的有限变形本构子程序（UMAT），为以后分析碳纤维增强热塑性复合材料的热力学变形行为奠定了扎实的数值基础；（4）建立了颗粒增强热塑性复合材料的损伤破坏细观力学模型，对一些重要的微结构参数影响进行了分析；（5）对于颗粒增强非定型复合材料的韧化机理进行数值模拟，获得了颗粒和基体两相之间的协同机理。在该项目资助下，负责人在2012年成功入选教育部新世纪优秀人才支持计划，另外本项目研究成果会有助于热塑性复合材料的微观结构优化、工艺参数拟定和结构力学分析，为它们的制备，设计和应用起到指导作用。