Multiscale modelling and characterisation of nanoreinforced composite laminates

高强度热固性环氧树脂广泛应用于航空航天、汽车、船舶和电子封装领域的高性能轻质复合层压板。然而，这些环氧树脂的断裂韧性相对较差，不能容忍缺陷。虽然使用某些普通添加剂可以有限地提高韧性，但这些添加剂也会导致高温机械性能的降低。因此，本工作的目的是用纳米填料代替这些常见的添加剂，并通过数值和实验确定这些纳米填料的类型、尺寸和数量对所研究的复合材料层合板的强度和层间断裂韧性的影响。在数值上，将开发三维多尺度模型，具有改进的粗粒度分子动力学，用于解释纳米填料与环氧树脂分子之间的相互作用。采用具有顺粒自由度的有效哈密顿量来代替系统原有的哈密顿量，从而在不影响精度的前提下提高仿真效率。此外，还将开发一种新的“纳米元件”，将原子/连续区域耦合在一起，以克服使用通常采用的连续统有限元（FE）在这些区域强制位移连续性时遇到的困难。有限元将以节点位置矢量的形式表述，以确保原子/连续体区域的能量的统一描述。实验上，将进行广泛的机械测试、超声波和纳米结构分析，以表征层压板的有效性能和纳米填料在环氧树脂中的分布。将进行精心设计的试验，以评估不同数量的纳米填料和不同温度下的有效粘结强度/刚度、层间断裂韧性和应变能释放率。这将使模型的验证和新型高性能复合材料的创造成为可能，并在下一代飞机上使用。这项工作将导致HQP在前沿研究、知识传播和技术转让方面的培训。

High strength thermoset epoxy resins are extensively used in high performance lightweight composite laminates for aerospace, automotive, marine and electronic packaging applications. However, these epoxies suffer from relatively poor fracture toughness and are intolerant of defects. Whilst limited improvement in toughness can be achieved using certain common additives, these additives also lead to reductions in high temperature mechanical properties. It is therefore the objective of this work to replace these common additives with nanofillers, and to determine the influence of the type, size and amount of these nanofillers on the strength and the interlaminar fracture toughness of the studied composite laminates both numerically and experimentally. Numerically, 3D multiscale model, with modified coarse-grained molecular dynamics that accounts for the interaction between the nanofillers and the molecules of the epoxy resin, will be developed. An effective Hamiltonian with course grained DOF will be used to replace the original Hamiltonian of the system, thus increasing the simulation efficiency without compromising accuracy. Furthermore, a new "nanoelement", that couples atomistic/continuum regions, will also be developed to overcome the difficulties encountered when enforcement displacement continuity across these regions using commonly adopted continuum finite elements (FE). The FE will be formulated in terms of nodal position vectors to ensure a unified description of energy in the atomistic/continuum regions. Experimentally, extensive mechanical tests, ultrasound and nanostructure analysis will be conducted to characterise the effective properties of the laminates and the distribution of the nanofillers in the epoxy. Carefully designed tests will be conducted to evaluate the effective bond strength/stiffness, interlaminar fracture toughness and strain energy release rate for varying amounts of nanofillers and different temperatures. This will enable the validation of the model and creation of new high performance composites for possible patent and use in the next generation aircrafts. This work will lead to the training of the HQP in leading edge research, dissemination of knowledge and technology transfer.