某型飞机前轮叉裂纹失效分析与解决措施

外场服役的两架某型飞机的前轮叉与活塞杆在连接孔上表面相同位置处出现了裂纹。断口分析表明，前轮叉裂纹为应力腐蚀裂纹，裂纹从内表面侧起源，并在应力作用下不断向外表面侧扩展．最终贯穿前轮叉与活塞杆连接处。同时，通过建立有限元模型对裂纹处应力分析，发现前轮又与活塞杆及螺栓之间的干涉量与干涉应力基本上呈线性关系，而且装配时摩擦系数对应力的影响可以忽略不计。由此得小轮叉出现裂纹的主要原因是轮叉与活塞杆及螺栓间的干涉配合在裂纹位置处造成的较大装配应力和腐蚀介质的作用引起的。因此．在装配过程中严格控制其干涉量，并提高轮叉表面的防护质量，是避免轮叉出现应力腐蚀裂纹的有效措施．

Failure Analysis and Solving Measures of Cracks on Front Wheel Fork of a Certain Type of Aircraft

Front wheel fork and piston rod occurs crack at same position of connection hole upper surface on a certain type of two aircrafts, which service on field. Through fracture analysis, the cracks on front wheel fork is stress corrosion crack, which originated from the inner surface side and constantly extend to outward surface side under stress, finally through the position which connects the front wheel fork with the piston rod. The establishment of the finite element model of stress at the crack found that the amount of interference, between the front fork and the piston rod/bolt, essentially has a linear relationship with interference stress. When assembling, the friction coefficient on impact of stress can be neglected. The interference fit between wheel fork with the piston rod as well as wheel fork with the bolt, can cause the larger assembly stress at the crack location, which is the main cause of cracks on wheel fork. Strictly control the interference amount and improve the quality of surface protection are the effective measures to avoid stress corrosion cracking.