Abstract
Vehicles are tested to prove the structural durability at proving ground. In case of fatigue failure of a prototype vehicle structure during this durability test, the vehicle design engineer investigates the shape of fatigue failure in a view point of crack initiation and propagation and makes modification to improve its structural durability. Nearly 70% of fatigue failures occur near the spot weld area, so it is necessary to investigate the position of crack initiation and propagation directions on spot weld area. This paper includes an analysis and test of fatigue crack initiation and propagation on high strength steel sheet with resistance spot welding. Finite element analysis was preformed to predict the position of fatigue crack initiation and propagation directions. The concept of strain energy density in inner surface around spot weld was adopted in order to predict fatigue crack initiation and propagation.