Automotive Body Fatigue Analysis – Inertia Relief or Transient Dynamics?

In this paper, the application of inertia relief and transient dynamics methods in vehicle structural stress analysis is considered. Then the principles and formulation of inertia relief approach are described briefly. Using MSC/NASTRAN finite element code, the two methods are used for a free-free beam model and the stresses in some selected elements are compared. The same procedure is repeated for a simplified vehicle body in white (B.I.W) model. The results of the analyses show that for obtaining satisfactory correct stresses using inertia relief approach, the frequency of the applied force should be much less than the fist natural frequency of the structure. It is also seen that the accuracy of the results for different elements may vary depending on the mode shape of the structure.