Adhesive reinforced friction stir welded thermoplastic tube-to-tubesheet hybrid joints

Thermoplastic materials are gaining popularity, because of their anti-fouling and chemically inert properties, for use in industrial applications that involve heating and cooling of highly reactive fluids. The current work studies the effect of adhesive reinforcement and radial clearance (RC) on developing friction stir welding (FSW)-based thermoplastic tube-to-tubesheet hybrid joints (TTHJs), which has applications in the thermoplastic heat exchanger and piping industries. The workpieces (sheets and tubes) made of carbon black reinforced high-density polyethylene were used. First, the effect of FSW parameters on the tube pull-out behavior was studied. The fractographic investigations (macroscopic and SEM) suggest that the FSW joints can fail in a brittle, ductile, or mixed manner, depending on the FSW conditions used. The FSW technique provides better load bearing capacity (326 N (0.0 RC), 517 N (0.5 mm RC)) compared to adhesive joints (226 N (0.0 RC), 206 N (0.5 mm RC)). For 0.0 RC, the adhesive reinforcement increased the load bearing capacity by 15.6 %. On the contrary, for 0.5 mm RC, the adhesive reinforcement negatively impacted the load bearing capacity and reduced it by 40.6 %. The FSW technique with 0.5 mm RC provides a higher leak path of 77 % remaining tubesheet thickness (> tube thickness) compared to that of 46.6 % (< tube thickness) achieved at 0.0 RC. However, the adhesive reinforcement can enhance the leak path of 0.0 RC FSW joints to around 100 % remaining tubesheet thickness (> tube thickness) by introducing the adhesive material at the tube-sheet interface.