Fractographic evaluation of welded joints of PPS/glass fiber thermoplastic composites

Abstract

Joints obtained by resistance welding of polyphenylene sulphide (PPS) laminates reinforced with bidirectional glass fiber (GF) fabrics were investigated by fractographic analyses. The welded joints were tested under lap shear loading at room temperature. The fracture surfaces were analyzed by scanning electron microscopy (SEM) technique. Electric resistance welding technique uses the matrix flow property, when the thermoplastic is heated above the softening temperature (for amorphous polymers) or above the melting temperature (for semicrystalline polymers), to promote the welding between the laminates. Fractographic aspects of the studied fracture surfaces show that the interfacial adhesion of matrix/heating element was efficient, with the presence of intralaminar and interfacial failures. The intralaminar failure was predominant in laminates with higher values of shear strength (9.6 MPa). On the other hand, interfacial failure was predominant in laminates with lower values of shear strength (1.9 MPa). The mechanical performance measured for the welded joints was attributed to the polymer chains interdiffusion mechanism in the welding region as well as to the good polymer anchoring in the mesh of heating element. The fractographic analyses performed proved to be an adequate tool because provide information to evaluate the quality of welding process of thermoplastic composites.