Overloading Effect on the Fatigue Strength in Resistance Spot Welding
,QWHUQDWLRQDO-RXUQDORI)DWLJXH ² Contents lists available at ScienceDirect International Journal of Fatigue journal homepage: www.elsevier.com/locate/ijfatigue Overloading effect on the fatigue strength in resistance spot welding joints of a DP980 steel ⁎ J.H. Ordoñeza, R.R. Ambriza, , C. Garcíab,G.Plascenciaa, D. Jaramilloa a Instituto Politécnico Nacional CIITEC-IPN, Cerrada de Cecati S/N, Col. Sta. Catarina, C.P. 02250 Azcapotzalco, Ciudad de México, Mexico b Facultad de Ingeniería, Universidad Autónoma de San Luis Potosí, Av. Dr. Manuel Nava No. 8, Zona Universitaria, C.P. 78290 San Luis Potosí, S.L.P., Mexico ARTICLE INFO ABSTRACT Keywords: Dual phase steel DP980 sheets were joined by resistance spot welding (RSW) process. Mechanical resistance of DP980 steel the welds was characterized by microhardness, tensile shear and fatigue tests. A significant hardness decreases Resistance spot welding was observed in the RSW lap joints with respect to the base material, which was attributed to phase transfor- Fatigue behavior mations during the heating and cooling of the steel. Fatigue Wöhler curves using a fixed load ratio of 0.1 were Compressive residual stresses obtained. It was found that the spot weld at the nugget interface close to the fusion zone induced a critical stress concentration factor, which decreased the fatigue life of the joints in the as-welded condition. Failure of the welds was initiated at the interface between welded sheets. Two predominant fatigue fracture modes were observed associated with mode I/III cyclic loading, which were correlated with the fatigue crack initiation and propagation stages. Compressive residual stresses were induced by a loading-unloading cycle on the spot welds, which tends to increase the fatigue life of the joints when compared to the as-welded condition.
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