Mechanical behaviour of friction stir spot welds of polycarbonate sheets

The present investigation is aimed at analyzing the influence of the processing speeds and processing times on mechanical behaviour of friction stir spot welding (FSSW) joints produced on polycarbonate sheets. The analysis in- volved the variation of rotational speed, tool plunge rate, pre-heating time, dwell time and waiting time. Mechanical characterization of joints was carried out by means of single lap shear test. Experimental tests were conducted according to two full factorial designs. First, an exploratory 25 full factorial plan was carried out to determine the most influencing factors determining the mechanical behaviour of FSSWjoints. Then, a33 optimization plan was performed by varying the most relevant process parameters among three levels. Therefore, analytical models were developed to predict the mechanical behaviour of welds (maximum shear strength, stiffness and absorbed energy) produced under different processing condi- tions. In addition, an artificial neural network (ANN) model was developed to improve the matching between experimen- tal measurements and model predictions. On the basis of the achieved results, a framework for improving the mechanical performances of thermoplastic joints was established. Accord- ing to the achieved results, tool plunge rate, dwell time and waiting time are the most influencing parameters for the joint strength and weld extension. On the other hand, pre-heating time and tool rotational speed have lower influence on the mechanical behaviour of FSSW joints.