腐蚀损伤诱发金属内部应力演化机理研究

For the complexity of initiation and propagation of the micro-crack at the corrosion damage area of the surface of metal structure under the corrosion environment, taking the methods of experiment, computer simulation and theoretical analysis, the stress evolution mechanism of crack initiation induced by the corrosion damage in metal is researched. Adopting the atomic force microscopy (AFM) in experiment to observe the dynamic evolution process of corrosion damage from atomic-scale to micro-scale and macro-scale on the surface of structure during the accelerated corrosion process of aluminum alloy plate which is widely used in aircraft structure, and extracting the information of structural evolution and analyzing it in real time. Based on the results of AFM corrosion tests, taking the cellular automation (CA) method, the electrochemical reaction and the diffusion process of the metal corrosion are simulate theoretically ,and the development rule of the corrosion damage accompanied with the time is obtained. Then, with the help of computer graphics image technology, the topologic characteristic graph of structure with corrosion damage can be obtained by extracting the corrosion information from the CA simulation. Finally, using the mesh-free method, the topology structure contained the corrosion information under external load is analyzed, and the stress distribution value around the corrosion damage is obtained. The results not only provide the theoretical basis for the micro-crack initiation and propagation at the area of corrosion damage, but also provide theoretical foundation and technical support for the safe operation of metal structure under complex service environment.

针对环境作用下金属材料表面腐蚀损伤处微裂纹萌生及扩展过程的复杂性，采用试验、计算机模拟与理论分析相结合的手段，对金属内部由腐蚀损伤诱发影响裂纹萌生的应力演化机理进行研究。试验上，采用原子力显微镜，对航空结构的铝合金板加速腐蚀过程中，材料表面腐蚀损伤从原子级到微观和宏观的动态过程进行观测，实时提取组织结构演化信息；理论上先结合模拟复杂系统的元胞自动机方法，用原子力显微镜观测腐蚀试验结果确定元胞自动机模型中的参数，对金属腐蚀过程中的电化学反应和扩散过程进行模拟，得到腐蚀损伤随时间的发展规律；再结合计算机图形图像处理技术，提取元胞自动机模拟结果中的腐蚀信息，获得结构含腐蚀损伤的拓扑特征图；最后用无网格方法，对包含腐蚀损伤信息的拓扑结构图在外载荷作用下进行分析，得到腐蚀损伤周围应力分布值。研究结果既为腐蚀损伤处微裂纹萌生及扩展提供理论依据，又为复杂环境下金属结构安全运转提供理论基础和技术支撑。

本项目以腐蚀损伤诱发金属内部应力演化机理为研究目标，采用试验与理论相结合的手段，对金属铝在环境与力学因素协同作用下的损伤演化过程进行研究，完成了以下重要工作：. 一是在试验室中, 通过加速腐蚀，利用原子力显微镜对金属铝表面腐蚀损伤从原子级到微观级和宏观的动态演化过程进行观测, 结果发现: 随着腐蚀时间增加，腐蚀坑的面积逐渐加大、深度逐渐加深，相邻的腐蚀坑会逐渐连通形成更大的腐蚀坑，最终逐渐遍布整个金属表面。 . 二是建立环境作用下金属铝表面腐蚀损伤形成及演化的元胞自动机模型,对材料表面腐蚀损伤的形成及扩展进行了研究。结果发现：材料表面腐蚀损伤形成及扩展与时间、溶液浓度和金属的溶解概率有关。. 三是建立求解含腐蚀损伤结构强度的理论模型,在元胞自动机方法研究材料腐蚀损伤演化规律的基础上，用开源计算机视觉库（OpenCV）结合图像分析技术对含腐蚀损伤结构的边界信息进行提取，结合光滑点插值法对结构内部的应力分布进行求解。. 四是建立腐蚀损伤处微裂纹萌生及微裂纹之间相互影响的模型,在C语言环境中开发完成了模拟腐蚀损伤处微裂纹萌生及扩展的程序，对金属表面腐蚀损伤处裂纹萌生及扩展进行了研究，结果发现：①微裂纹尖端的应力集中扰乱原子间的力平衡，导致相变；②微裂纹间的相互作用是通过应力场传递的；③微裂纹之间的相互作用不仅与裂纹之间的距离有关，而且与裂纹的大小有关；④微裂纹间相互作用对材料的弹性模量没有影响，但会影响材料的强度极限。. 五是建立环境作用下金属材料从腐蚀损伤到微观裂纹和宏观裂纹一体化破坏的元胞近场动力学模型，弥补了用光滑点插值法求解结构动强度需要做特殊处理不足。