In the present paper, effects of welding current, welding time, electrode pressure and holding time on the weld nugget size were studied. A failure mechanism was proposed to describe both interfacial and pullout failure modes. This mechanism was confirmed by SEM investigations. In the light of this mechanism, the effect of welding parameters on static weld strength and failure mode was studied. Then, an analytical model was proposed to predict failure mode and to estimate minimum nugget diameter (critical diameter) to ensure pullout failure mode in shear tensile test. On the contrary to existing industrial standards, in this model, critical nugget diameter is attributed to metallurgical characterisation of material (weld nugget hardness to failure location hardness ratio), in addition to sheet thickness. For a given sheet thickness, decreasing H WN H FL increases interfacial failure mode tendency. The results of this model were compared with experimental data and also with the literature.
The effects of weld nugget size and expulsion on the performance of low carbon steel resistance spot weld have been investigated in the present paper. Failure mode, peak load and failure energy obtained in tensile-shear test have been used to describe the performance of spot weld. The influence of voids and porosity as well as electrode indentation associated with expulsion on peak load and failure energy is discussed. The results showed that although expulsion does not reduce the load carrying capacity of spot welds, it decreases their energy absorption capability which was attributed to the change of failure location due to excessive electrode indentation associated with expulsion.
By developing mathematical models for the arc and the weld pool in the GTAW process, the effect of the electrode tip angle on both arc and weld pool was studied. The present paper is concerned with the model for the arc. By applying a variable cathode surface area, the effect of the electrode tip angle (in the range of 10 to ) on the arc properties, especially on the anode current density, heat flux and gas shear stress over the weld pool, was investigated. Comparison of the calculated results with the available experimental data for 200 A arcs of different lengths showed that the model predictions for temperatures higher than 10 000 K are in very good agreement. For temperatures less than 10 000 K, some modifications were necessary to take into account the absorption of heat by the cooler parts of the arc. It was found that by increasing the electrode tip angle, the anode spot at the weld pool surface tended to be more localized. This led to a higher maximum heat flux and anode current density. On the other hand, the gas shear stress increased on decreasing the electrode tip angle.
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