Damage-tolerant, delamination-free high-performance fibre-reinforced polymer composites

纤维增强聚合物复合材料(FRP)的多尺度、各向异性结构导致了复杂的破坏行为。因此，会发生不同类型的失效，微观层面上的母体失效会影响到所有更高观察层面上的失效过程。分层是指FRP中不同取向的层的分层，是一种关键的破坏模式，因为它导致层合板的承载能力显著降低，特别是在压缩载荷或层压板平面外的载荷下。薄层指的是层厚小于60m的复合材料。对无缺口的多向薄层板进行的准静态UD拉伸试验表明，基体开裂的起始时间推迟到完全断裂之前，显著提高了强度。然而，抑制基质损伤会导致缺口层压板的强度显著降低，因为不会发生分层引起的应力集中退化。对薄层板基损伤的抑制也会影响低速冲击载荷造成的损伤。然而，由于层结构设计中的扩展自由度，薄层叠层也允许采用全新的方法来影响失效行为。因此，一种影响FRP损伤行为的新方法是使用新颖的、受自然启发的层结构。在甲壳类动物受冲击的身体部位发现的螺旋层结构，即所谓的Bouligand结构是很有前途的。申请人的初步工作表明，使用仿生螺旋结构可以控制玻璃钢的破坏行为，从而完全抑制分层，并且在最终破坏之前只发生亚临界基质损伤：-通过薄层和层间的小角度可以实现无分层的铺层结构。-通过薄层和小层角可以实现几乎没有缺口的层积。-与传统的层合结构相比，冲击损伤后的剩余强度提高了15%。然而，结果也引发了一些问题：单层必须有多薄，层之间的夹角必须有多小才能充分利用效果？必须考虑的是，这些几何因素基本上是由纤维的硬度和层间能量释放率GIIc决定的。-从亚临界基质开裂到层间分层的损伤模式的临界角和边界层厚度是多少？本研究项目的目的是全面了解螺旋层板结构的力学行为，并对其进行建模，以减少高实验工作量，从而使螺旋层板在技术上可用。

The multi-scale, anisotropic structure of fibre-reinforced polymer composites (FRP) leads to complex failure behaviour. Thus, different types of failure occur and the matrix failure at the micro level influences the failure process at all higher levels of observation. Delamination refers to the layer separation (delamination) of differently oriented layers in an FRP and is a critical failure mode as it leads to a significant reduction in the load-bearing capacity of the laminates, especially under compressive loading or loads outside the laminate plane. Thin-ply refers to composites with a layer thickness less than 60 m. Quasi-static UD tensile tests on unnotched, multidirectional thin-ply laminates have shown that the initiation of matrix cracking is delayed until just before complete fracture, significantly increasing strength. However, suppression of matrix damage results in a significant reduction in the strength of notched laminates, as no degradation of stress concentrations due to delamination occurs. The suppression of matrix damage in thin-ply laminates also affects the resulting damage from low velocity impact loading. However, thin-ply laminates also allow completely new approaches to influence the failure behaviour due to the extended degrees of freedom in the design of the layer structure. Thus, a new approach to influencing the damage behaviour of FRP is the use of novel, nature-inspired layer structures. Promising are helicoidal layer structures found in impact-loaded body parts of crustaceans, so-called Bouligand structures.As shown in the applicant's preliminary work, the use of bio-inspired helicoidal ply structures can control the failure behaviour of FRP such that delamination is completely suppressed and only subcritical matrix damage occurs before ultimate failure:- Delamination-free ply constructions can be realised by thin-ply and small angles between the plies.- Layer build-ups with almost no notch effect can be achieved by thin-ply and small layer angles.- The residual strength after impact damage was improved by 15% compared to conventional laminate structures.However, questions also arise from the results:- How thin must the single ply be and how small must the angle between the plies be to take full advantage of the effects? It must be taken into account that these geometric factors are essentially determined by the stiffness of the fibres and the interlaminar energy release rate GIIc.- What are the critical angle and the boundary layer thickness at which the damage mode changes from subcritical matrix cracking to interlaminar delamination?This research project aims to fully understand the mechanical behaviour of helicoidal laminate structures and to model the behaviour in order to reduce the high experimental effort and thus make helicoidal laminates technically usable.