Effect of Wall Thickness and Flow Distance behind an Obstacle on the Weldline Strength of Thermoplastic Composites

Abstract

The strength of the weldline behind an obstacle in injection molded thermoplastic composites was investigated in this study. The effects of part thickness, glass-fiber length, and concentration on the weldline strength at different positions behind the obstacle were examined. The results showed that the mechanical properties of the specimen containing weldline were much lower as the fiber length and content increased. Considering the effect of part thickness on the weldline strength, it was observed that the weldline strength decreased as the part thickness increased. This was due to the fiber orientation and the void generation within the molded parts. The results obtained for the weldline strength at various positions along the weldline indicated that the weldline strength tended to increase with the increase of flow distance, especially for polypropylene containing 40 wt% long-glass-fibers. The explanation for this could be associated with the change in fiber orientation during the flow development.