研究了飞机主起落架半轮叉在使用过程中出现于30CrMnSiNi2A焊缝边缘的裂纹的形态、断口特征、形成及扩展原因。发现焊缝加强高凸部分和内侧板弧形表面的交角过小,引起应力集中；焊趾表层疏松及打磨的痕迹、蚀坑等促使裂纹萌生；主起落架在滑行、刹车、转弯的力矩使裂纹扩展。

This paper mainly discusses the cracks occurred at th welding edge of 30CrMnSiNi2A steel structure used for aircraft main landing gear, studies the crack's shape and fracture characteristics and analizes the couses of crack's formation and propagation. It is thought that the included angle between the projection of the welding seam and the camber surface of inner sideboard is too small, causing the stress concentration, the porosity of welding root, the scars of grinding and the corrosion pits may cause the occurrence of cracks, and the greater moment of force in the aircraft taxiing, braking and turning mahes it possible for cracks to develop.