Investigation on polypropylene friction stir joint: effects of tool tilt angle on heat flux, material flow and defect formation

Abstract

Tool tilt angle (TTA) is a critical factor that can control material flow in polymeric materials' friction stir joining (FSJ). This study selected a TTA range between 0° to 4° for FSJ of polypropylene (PP) polymer sheet. A modified computational fluid dynamic (CFD) technique was implemented to gain a deep understanding of the effects of TTA during FSJ of PP. The PP joint's internal flow, defect formation, heat generation, and tensile strength were investigated experimentally. The fracture surface of tensile samples was analyzed by scanning electron microscopy (SEM). Heat generation, heat flux, and defect formation results from simulation were evaluated by experimental tests output. The results indicate that the PP flow during FSJ is susceptible to TTA. Non-uniform volumetric weight transfer was caused at higher TTA in the joint line, which leads to tilted heat flux. At higher TTA, the generated heat increases, leading to PP exit from the joint line and internal gaps. According to selected parameters, the most robust joint (66 MPa) was produced at 1° TTA. The main reason for the mechanical properties of the PP joint was a dimension of the stir zone and internal defects. Shrinkage gaps were the root of crack initiation during the tensile test, and some local stretching in the fracture surface of the tensile sample after the test was detected.