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涂层是飞机的主要防腐体系,涂层局部破损失效后往往对其他完好区域产生影响,但有些位置比较隐蔽难于发现,给飞行安全带来了隐患。模拟飞机服役环境,对钛-钢螺栓搭接件进行腐蚀试验,基于电偶腐蚀数学模型,选取相应的边界条件,用有限元法分析了搭接件表面涂层失效原因及影响。结果表明,涂层失效过程分三个阶段,电偶腐蚀效应使搭接件周围形成电场,在电势梯度作用下,Cl-发生定向加速移动,导致电渗起泡。随着涂层失效面积的增加,阴、阳极面积比例不断变小,阳极腐蚀得到减轻;最大腐蚀电流密度的位置发生变化,数值变小,降低了发生点蚀的风险。通过对搭接结构周围溶液腐蚀电场的计算,可以预测涂层失效区域,为飞机涂层体系的维护保养提供技术支持。
The coating is the main anticorrosive system of the aircraft. After the coating partially fails to be damaged, it often affects other intact areas. However, some locations are relatively invisible and difficult to find, posing hidden dangers to flight safety. The service environment of the aircraft was simulated, and the corrosion test of Ti-steel bolt lap joint was carried out. Based on the mathematical model of galvanic corrosion, the corresponding boundary conditions were selected, and the causes and effects of lap coating surface failure were analyzed by finite element method. The results show that the coating failure process is divided into three stages. The galvanic corrosion effect causes the electric field to form around the overlap. Under the action of the potential gradient, Cl- accelerates and moves in directional direction, resulting in electroosmotic blistering. With the increase of coating failure area, the proportion of area of anode and cathode became smaller and the corrosion of anode decreased. The location of maximum corrosion current density changed and the value decreased, which reduced the risk of pitting corrosion. By calculating the electric field of the solution around the lap structure, the failure area of the coating can be predicted, providing technical support for the maintenance of the aircraft coating system.