Time-temperature-dependent mechanical durability analysis of short (glass) fiber-reinforced polyethylene terephthalate injection molding composites with weld line

The mechanical property and long-term durable life of short fiber composites are inevitably subjected to internal and external influences during molding and afterwards, such as weld, temperature, stress type, and so on. This study was concerned with the influence of weld on mechanical properties of short glass fiber reinforced polyethylene terephthalate injection molding composites and the investigation of their tensile properties at different temperatures and tensile speeds with varying fiber contents. The weld strength was about 50-60% less than the tensile strength at different temperatures and tensile speeds. As the fiber content increased from 15 wt% to 30 wt%, the weld strength was reduced by 10%. The tensile and weld strength were in general inversely proportional to the temperature and linearly proportional to the tensile speed. Tensile modulus showed an inverse association with temperature and a mostly non-linear relation with the tensile speed. The weld line integrity in tensile strength was independent of tensile speed and temperature below the glass transition temperature level. Morphology evaluation testified that the higher test speed emanated better fracture surface fiber-resin adhesion properties with comparatively brittle fracture tensile behavior. The time-temperature superposition principle was applied to find the scope of long-term durability, lifetime prediction and to describe the viscoelastic properties of the welded glass fiber reinforced polyethylene terephthalate composites. An Arrhenius type of shift factor was obtained to fit the tensile strength data which was independent of the fiber contents of the welds. The experimental results can provide a valuable reference for the design and manufacture of short fiber-reinforced composites in long-term durability applications.