Characterization of bolt hole residual stresses for assessing structural behavior of truck frame rails

Chassis frame rails in a truck are load bearing structural members that integrate vehicle power train with superstructure to form a complete vehicle. Large numbers of bolt holes that are cut into these frame side members act as joineries and points of attachments for various sub systems of the truck. While bolt holes are unavoidable due to its primary functional importance, the near hole residual stresses remaining from hole cutting operations may play a significant role in deciding the life of frame rail sections as they lead to early initiation of fatigue cracks around bolt hole surface. In order to assess the extent of plastic deformation and resulting residual stress pattern in near hole areas of bolt holes, experimental investigation through microstructure analysis, micro-hardness and X-ray diffraction measurements has been taken up. The hole cutting operations considered for this exercise are drilling, punching, laser cutting and water jet cutting used to cut holes on truck frame rail sections. Apart from this, an assessment of shot-peened hole surface was also taken up to understand the effect of shot-peening on structural behavior of frame rail bolt hole sections. The experimentally measured near hole residual stress profiles can be considered as initial conditions for further numerical analysis to study the influence of bolt hole residual stresses on fatigue life of frame rail sections. © (2012) Trans Tech Publications, Switzerland.