Papers by Keyword: Spot Welded Joint

Abstract: Deformation response and failure process of a spot welded joint are investigated in this study. For this purpose, a cross-tension spot welded joint sample made of dual phase steel sheets (DP600) is prepared and tensile tested to failure. Complementary FE simulation of the test is performed. The FE model acknowledges the variation of properties across the spot welded region. Rice-Tracey ductile damage model is approximated and employed in the simulation. Close comparison of load-displacement curves and deformed shape with measured values serve as validation of the FE model. Results show that FE simulation with damage-based model adequately predicts tensile deformation and failure of the spot welded joint. Tensile failure of the joint is confined to the heat affected zone and heat affected/fusion zone interface of the joint. Localized through-thickness necking of the sheet metal is captured. In addition, the predicted fracture of the spot welded joint is accompanied by localized extensive plastic deformation.

Abstract: A finite element (FE) model incorporating a progressive material damage with Rice-Tracey damage initiation criterion is developed in this study. The relationship between local ductility reduction and stress triaxiality was established experimentally. The FE model was validated by comparisons of load-displacement response of the spot welded lap joint specimen at displacement rate of 5 mm/min and the observed ductile failure mechanism. Results show that Rice-Tracey damage initiation criterion used is sufficient to reproduce the observed ductile failure response of the specimen. Failure of the spot welded lap joint is initiated at the HAZ/fusion zone interface with localized necking.

Abstract: In this paper, fatigue tests and finite element analyses are carried out on spot welded joints of mild steel (270MPa class) and ultra-high strength steel (980MPa class) in order to investigate the influence of strength level of base steels on fatigue strength and fracture morphology of spot welded joints. From the fatigue tests the following results are obtained: (1) Fatigue limit of spot welded joints is almost the same in both steels. (2) Fatigue fracture morphology of spot welded joints depends on the load level in the ultra-high strength steel, but not in the mild steel. From discussion based on the finite element analyses the following results are obtained: (3) The fatigue limit of spot welded joints can be predicted by stress intensity factors for a nugget edge, fracture criterion for a mixed mode crack and threshold value for fatigue crack growth in base steel. (4) Plastic deformation around a nugget in spot welded joints strongly affects the fatigue fracture morphology.

Abstract: An effective way to reduce the weight of vehicle body seems to be application of new materials, and such trend is remarkable. Among the various materials for automobile body, stainless steel sheets and cold rolled steel sheets are under the interests. However, in order to guarantee reliability of new material and to establish the long life fatigue design criteria for body structure, it is necessary to assess spot weldability and fatigue strength of spot welded lap joints fabricated under optimized spot welding condition. In this paper, spot weldability of stainless steel sheets, STS301L and STS304L, and cold rolled steel sheets, SPCC and SPCD. Fatigue strength of lap joints spot welded between similar and dissimilar materials were also assessed.

Abstract: An effective way to reduce the weight of vehicle body seems to be application of new materials, and such trend is remarkable. Among the various materials for vehicle body, stainless steel sheets and cold rolled steel sheets are under the interests. However, in order to guarantee reliability of new material and to establish the long life fatigue design criteria for body structure, it is necessary to assess spot weldability and fatigue strength of spot welded lap joints fabricated under optimized spot welding condition. In this paper, spot weldability of stainless steel sheets, STS304L and STS316L, and cold rolled steel sheets, SPCC and SPCD. Fatigue strength of lap joints spot welded between similar and dissimilar materials were also assessed.

Abstract: Resistance spot welding is used extensively to fasten sheet for automotive applications. In many components, these welds should maintain their integrity under severe loading conditions. However fatigue strength of the spot welded joint is considerably lower than base metal due to stress concentration at the nugget edge, and is influenced by its geometrical and mechanical factors such as welding condition and etc. In this paper, it is estimated that effect of strain rate variation on fatigue life of spot welded joint. The analytical method proposed to overcome above difficult using lethargy coefficient concept for evaluating the fatigue life cycle of spot welded joint. The reliability of the life cycle is completed by comparing with the life cycle obtained by fatigue test for the specimen with the welding current. And the above procedure is numerically extended to get the life of dynamic strain rate region.