Integrated Computational-Experimental Study of Microstructurally Short Crack Propagation in AA7xxx alloys

新一代7xxx系列铝合金具有比强度高、生产成本低的特点，是飞机结构应用中常用的材料。然而，这些合金表现出增加的易感性环境辅助开裂（EAC），这需要更好地了解。因此，这些合金的EAC性能是航空航天工业日益关注的一个领域。目前对EAC的关键早期阶段知之甚少，发表的数据很少。因此，该项目旨在提高对裂纹起始的理解，特别是微观结构短裂纹如何生长，以及它们如何过渡到可能继续导致失效的可行长裂纹。在短裂纹阶段，特定的裂纹前缘几何形状和微观结构的相互作用（如邻近裂纹和晶界）主导了裂纹的扩展。然而，现有的短裂纹驱动力模型忽略了这些细节，因此其预测能力有限。该项目的目的是通过考虑空间分辨裂纹前缘几何和微观结构相互作用来改进现有的裂纹扩展模型。从最先进的原位测试中获得的时间和空间分辨率的三维x射线计算机断层扫描（CT）数据将直接导入有限元模拟中，以获得裂纹尖端应力场和裂纹前缘驱动力的局部描述。目标是用局部微观结构细节补充现有的全局裂纹扩展模型。这将有助于我们了解为什么有些裂缝会扩展形成长裂缝，而另一些裂缝在很小的时候就停止了，以及为什么在某些情况下，被阻止的裂缝会重新开始生长。

New generation 7xxx series Al alloys are commonly used material in aircraft structural applications due to their high specific strength and low production costs. However, these alloys exhibit an increased susceptibility environmentally assisted cracking (EAC) which needs to be better understood. The EAC performance of these alloys is thus an area of growing concern for the aerospace industry.The critical early stages of EAC is currently poorly understood with little published data. This project will thus aim to improve understanding of the initiation of cracks and specifically how microstructurally-short cracks grow, and their transition to a viable long crack which may go on to cause failure. During the short-crack phase, growth is dominated by the specific crack-front geometry and microstructural interactions, such as neighbouring cracks and grain boundaries. However, existing models for short-crack driving forces neglect these details and are thus limited in their predictive capability.The aim of this project is to refine the existing crack growth models, by considering the spatially-resolved crack-front geometry and microstructural interactions. Temporally and spatially resolved 3D X-ray computed tomography (CT) data of crack propagation from state-of-the-art in-situ testing will be directly imported into FE simulations to obtain the crack tip stress field and a local description of crack-front driving forces. The objective is to complement existing global crack-propagation models with local microstructural detail. This will provide insight into why some cracks propagate to form long cracks whilst other cracks arrest whilst they are still small, and why in some cases the growth of arrested cracks restarts.