PSI - Issue 5

Shayan Eslami et al. / Procedia Structural Integrity 5 (2017) 1433–1438 Shayan Eslami et al./ Structural Integrity Procedia 00 (2017) 000 – 000

1434

2

the welding tool, under an axial force. The solid-state welding process refers to the welding temperature lower than the base materials ’ melting point, helping to preserve the mechanical properties of the parent materials. However, polymeric FSW is not an absolute solid-state welding process, but mixture of solid and liquid molecular chains due to the different molecular weights of polymers [2, 3]. The schematic demonstration of the most common FSW tool (consists of rotating shoulder and probe) for lap-joint configuration is illustrated in Figure 1. Using conventional FSW tool (rotating shoulder), the shoulder is responsible for generating most of the frictional heat, while the probe stirs the plastically deformed materials together under the axial force. However, strong welds are very hard to obtain using the conventional FSW tool design concept, due to formation of flash defects, which causes the soft materials to push out of the weld bead [4]. In order to achieve high performance welds with good surface quality for polymers, a stationary shoulder is essential to avoid formation of the flash defects by pushing down the molten material into the weld bead under the axial force. However, with absent of a rotating shoulder, most of the required heat is generated by the rotating probe.

Figure 1-Schematic of typical FSW lap-joint [5].

The FSW process proved to be a reliable method producing joints with high mechanical properties. Transportation industry gradually being dominated by this technique due to its numerous advantages over other available welding methods [6, 7]. Tensile and fatigue assessments are the most common testing methods to evaluate joint efficiency. Fatigue failure is a critical issue especially in transportation industry due to the different loading conditions [8]. Fatigue life evaluation of FSW joints have expanded recently due to the increasing demands of FSW process in industry. It was noticed that fatigue life of the specimens fabricated by FSW process were higher than traditional fusion welding methods such as MIG and TIG [9]. However, the literature suffers from absence of fatigue assessment and lifetime analysis of FSW polymeric materials, and more development is required in this area. In this study two commercially used polymers used to weld in the lap-joint configuration to evaluate the fatigue life of the welded specimens under cyclic shear loading conditions.