Investigation of fatigue behavior in outer tie rods in passenger cars

Tie rods which are subjected to static, dynamic and bearing loads are one of the important linkage components of the steering gears. Especially their fatigue endurances should be high since they are a safety component in steering gear. In case at design phase, a breakage is detected before completion of tie rod fatigue life, hardening process is applied to outer tie rod ball pin in order to be completed fatigue life. Nowadays many hardening process methods are available. Selecting the method which has the property of improving the surface quality is an important point in terms of developing the process. In this study, fatigue behavior has been evaluated for the outer tie rods which are subjected to fatigue loads at the vehicle. The study aims to increase the strength of the ball pin against fatigue and to improve the surface properties by deep rolling which is the hardening process applied to the ball pins. Within the scope of the study, the effects of deep rolling process on fatigue life has been evaluated by performing fatigue test to the specimens which are implemented and not implemented deep rolling. Surface hardness, surface roughness and geometric dimensional inspections were carried out.