PSI- Issue 9

Tareq Rahman Mahmood et al. / Procedia Structural Integrity 9 (2018) 71–85 Tareq rahman mahmood , et al./ Structural Integrity Procedia 00 (2018) 000–000

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time significantly affect these characteristics, see Fig. 16. The volume fraction of molten zone is a function of input heat which is governed by the welding parameters including welding current and welding time. In general, the increasing of the welding current causes increasing in the tensile strength rapidly. The liquid metal during nugget formulation is mashed to transform into a spatter by the excessive welding current and electrode force. Therefore, the decreasing tensile strength with increasing in electrode forces due to reduce the heat resistant, see Fig. 17. The role of the electrode force in forming nuggets in the RSW process is crucial. In general, by increasing the welding current, the strength increases. By reaching a maximum amount, the strength decreases, see Fig. 9. At higher electrode force there is a further decrease in strength because of excessive electrode force leading to enlarge the contact area between specimen and electrodes. Thus, the nugget size will be decreased by this effect.

Fig. 16. 3D surface interaction between welding current and welding time for low carbon steel with thickness 0.9 mm.

Fig. 17. Interaction between welding time and electrode force for HSLA steel.

The effect of the electrode force at higher welding currents depends greatly on the welding time, see Fig. 18. Because at the higher welding time (higher than 35cycle), the increasing of the electrode force will decrease nugget strength. This is also due to the penetration of the electrodes into the specimens (Al-Mukhtar 2016; A. Al-Mukhtar and Doos 2013). The effect of electrode force is crucial at high time.