A new car in operation of only 8,000 km, because of malfunction, resulting in lost control and rammed into the edge of
the road, and then the basic vehicle scrapped. According to the investigation of the site, it was found that the tie-rod of
the car had been broken. For the subjective analysis of the accident and identifying the true causes of rupture of the tierod,
a series of studies, from the angle of theory to experiment on the bended broken tie-rod, were conducted. The
mechanical model was established; the stability of the defective tie-rod was simulated based on ANSYS software.
Meanwhile, the process of the accident was simulated considering the effect of destabilization of different vehicle speed
and direction of the impact. Simultaneously, macro graphic test, chemical composition analysis, microstructure analysis
and SEM analysis of the fracture were implemented. The results showed that: 1) the toughness of the tie-rod is at a
normal level, but there is some previous flaws. One quarter of the fracture surface has been cracked before the accident.
However, there is no relationship between the flaw and this incident. The direct cause is the dynamic instability leading
to the large deformation of impact loading. 2) The declining safety factor of the tie-rod greatly due to the previous flaws;
the result of numerical simulation shows that previous flaw is the vital factor of structure instability, on the basis of the
comparison of critical loads of the accident tie-rod and normal. The critical load can decrease by 51.3% when the initial
defect increases 19.54% on the cross-sectional area, which meets the Theory of Koiter.