Measuring deformation and mechanical properties of weld lines in short fibre reinforced thermoplastics using digital image correlation

Weld lines in injection moulded short fibre reinforced thermoplastics can significantly reduce the mechanical strength of a product. However, knowledge about the mechanical properties in the weld line region is limited. A reason for this is the difficulty in measuring strains at small scales. In this study, the feasibility and usefulness of high spatial resolution digital image correlation to measure strain profiles in the weld line region is demonstrated on a short fibre reinforced polyamide. The elastic modulus of weld lines in the reinforced material was determined to be equal to the matrix modulus, while the weld line strength was higher than the bulk matrix material. A suggested explanation for the strength increase is that fibres, although not crossing the weld line, reinforce it by preventing necking.