垂尾方向舵悬挂点螺栓断裂分析及改进

目的 分析某型飞机在使用中其方向舵第4悬挂点连接螺栓出现不同程度断裂损伤的原因，并进行设计改进。方法 从宏观和微观2个方面研究螺栓的断口形貌和特征，对螺栓材料进行金相组织分析和力学性能测试，与同类型飞机相同位置螺栓的结构和功能进行对比分析。结果 螺栓断口边缘无明显的腐蚀和氧化特征，无有害的夹杂物和磷化物，硬度及拉伸强度符合材料力学性能要求。该型飞机方向舵第4悬挂点连接螺栓的结构较同类型飞机相同位置的螺栓结构应力集中更加明显，材料强度更低，存在设计缺陷。结论 连接螺栓断裂性质为疲劳断裂，螺栓受到异常的拉伸和弯曲循环载荷作用是导致其疲劳断裂的主要原因。基于裂纹原因及性能对比分析提出的设计改进方案，在螺栓选材、强度、刚度和耐久性等方面符合飞机结构设计规范，经验证，满足飞机装配技术要求，实践表明，能够确保飞机寿命期的安全使用。

Fracture Damage Analysis and Improvements on the Bolt at Suspension Point of Vertical Tail's Rudder

The fracture damages at different levels of No.4 connecting bolts at vertical tail''s rudder are found in the service of an aircraft, this paper aims to analyze the causes and make design improvement measures. In this paper, the fracture morphology and characteristics of the bolt are studied from the macrocosm and microcosm, the microstructure and mechanical properties of the bolt materials are analyzed, and the structure and function of bolts in the same position as those in the same type of aircraft are compared and analyzed. The results show that the fracture edge of the bolt has no obvious corrosion and oxidation characteristics, no harmful inclusions and phosphide, and the hardness and tensile strength meet the requirements of the material properties. The structure of the connecting bolt at the 4th suspension point of the rudder of this type of aircraft is more obvious in stress concentration and lower in material strength than that of the same type of aircraft at the same position, this link structure has design defects. The fracture property of the connecting bolt is fatigue fracture, and the main cause of fatigue fracture is that the bolt is subjected to abnormal tension and bending cyclic load. According to the results of bolt fracture and performance analysis, the proposed design improvement scheme can meet the requirements of bolt material selection, strength, stiffness and durability in aircraft structural design specifications. It has been verified that the solution meets the technical requirements of aircraft assembly and can ensure the safe use of the aircraft throughout its life.