Influence of Weld Lines on the Mechanical Properties of Talc Filled Polypropylene

Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). In this paper, two different injection molding tests were completed. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line region. Tensile samples were cut at different locations along the weld line on the injection molded plaques. The test results showed that both UTS and fracture strain increase when the sample locations are away from the insert. This trend is attributed to different meeting angles. Second, standard ISO tensile bars with and without weld line were injection molded to identify the size of the weld line affected zone. A FEA model was built in ABAQUS, where the tensile sample was divided into two different regions, the solid region and the weld line affected region. Stress-strain relationships of the solid region were derived from tensile tests of solid bars, while the mechanical properties of weld line affected zones were characterized from the weld line samples using Digital Image Correlation (DIC) analysis. By changing the width of the weld line affected zone in the FEA model, and comparing the predictions with experiment data, it is possible to find out the approximate width of the weld line affected zone.