汽车转向横拉杆断裂失效分析

Stability and Failure Analysis of Steering Tie Rod

为对事故原因进行仲裁分析,找出横拉杆断裂的真实原因,对发生弯曲断裂的横拉杆从理论及实验等方面进行了系列研究,建立了力学模型,利用有限元软件模拟了含缺陷横拉杆的结构稳定性,并模拟事故的发生过程,考虑了汽车速度及冲击方向对失稳的影响,同时对事故拉杆进行了表面宏观检验、化学成分分析、显微组织分析以及断口扫描电子显微镜分析.结果表明,该横拉杆的材质正常,韧性良好,但具有早期缺陷,事故发生前断裂的横截面上约有1/5的区域已经开裂.而该缺陷与本次事故没有直接的因果关系,事故的直接原因是动态失稳造成转向横拉杆在冲击载荷作用下发生了大变形屈曲.横拉杆的初始缺陷大大降低了其安全系数,通过对比事故横拉杆与正常拉杆临界载荷的数值模拟结果发现,结构稳定性对初始缺陷十分敏感,当初始缺陷达到横拉杆横截面积19.54%时,其临界载荷降低51.3%,与Koiter理论结果极为相似.

For the arbitrary analysis of an accident and to identify the true causes of rupture of the tie rod,a series of studies,from theories to experiments on the bended broken tie rod,are conducted. A mechanical model is established and the stability of the defective tie rod is simulated based on ANSYS software. Meanwhile,the process of the accident is simulated considering the effect on destabilization of different vehicle speeds and directions of the impact. Simultaneously,macro graphic tests,chemical composition analysis,microstructure analysis and SEM analysis of the fracture are implemented. The results show that： 1） the toughness of the tie rod is at a normal level,but there are premature flaws. One quarter of the fracture surface has cracked before the accident. However,the flaw has no direct relationship with this incident. The direct cause of the accident is the dynamic instability caused by the large deformation of the car under impact loading. 2） The safety factor of the tie rod declines greatly due to the premature flaws and the result of numerical simulation shows that premature flaw is the vital factor of structure stability on the basis of the comparison of critical loads between the accident tie rod and a normal one. The critical load decreases by 51. 3% when the initial defect reaches 19. 54% of the cross-sectional area,which meets the standards of Theory of Koiter.