Experimental and numerical fatigue behavior analysis of a plastically deformed passenger car tie rod

Passenger car tie rod is generally tested and analyzed by assuming that it has never been previously subjected to any load and no permanent deformation has occurred on it. However, the tie rod is subjected to various forces while driving and these forces can cause plastic deformation at the tie rod end. If tie rod is deformed to a value that does not affect the driving stability of the vehicle, the driver may not be able to detect it and continue driving. As a result, fatigue life can be influenced by this pre-deformation if repeated forces are applied to tie rod, which has undergone pre-deformation, during driving. The tie rod end can endanger the driving safety by causing fatigue damage earlier than the estimated life. In this thesis, fatigue strength, which is an important criterion for the design of passenger car tie rod end is investigated both on standard tie rod ends which were not pre-deformed and on tie rod ends which were deformed with a preload that caused plastic deformation on the part. The finite element method is used to determine the preload to be applied on the tie rod end and then fatigue tests and finite element analyses are performed at three different fatigue loads. The finite element analysis using Bergmann, Morrow and Smith-Watson-Topper fatigue parameters are compared. The effect of preliminary deformation on fatigue life is analyzed experimentally and numerically and finally the results are compared. For this purpose, analyses have been performed using the finite element method for the pre-deformed tie rod ends. In conclusion, the approach followed here demonstrate how the predeformation affects the fatigue life of the tie rod end which could be implemented in design and analysis studies.