Fatigue Strength of Spot Welded Joints under Corrosive Envirnoments

Abstract

To investigate effects of the corrosive environments on the fatigue strength of spot welded joint, the fatigue strength of spot welded joint which have suffered from corrosion under the outdoor exposure is first investigated. Next, in order to investigate effects of the corrosion caused by highway de-icing salt on the fatigue strength of spot welded joints in some countries, the fatigue tests of spot welded joints in the salt water spray and the salt water dipping are carried out. For the purpose of comparison, moreover, the fatigue test of spot welded joints in the pure water dipping for some test specimens are also intended to try.
Test specimens used are of mild steel (SPCC) in most experiments and 440 MPa- and 780 MPa-classes high strength steels in a few experiments, which thicknesses are all 0.8 mm.
As the results, unignorable decrease of the fatigue strengths of spot welded joints in each case is found. Moreover, in the experiments under the outdoor exposure and the salt water spray, it is proved that sheet separation of spot welded specimen plays an important role in the decrease of these fatigue strengths.