Full-field measurement of strain and temperature in tensile testing of short fibre-reinforced thermoplastic composites

Short fibre-reinforced thermoplastic composites are increasingly popular in the automotive industry thanks to low cost, short cycle times and recyclability. They can be easily injection-moulded into complex shapes. However, compared with thermoset composites or metals, they are more sensitive to environmental and loading conditions. The aim of this study is to characterise the tensile behaviour of injection-moulded short glass fibre-reinforced polyamide 6 (PA6) under conditions that are representative of in-service applications. This is done by varying fibre orientation, temperature, humidity, and strain rate. The material is heterogeneous and has a complex microstructure. This calls for a dedicated measurement setup during tensile testing. Strains are mapped full-field on the specimen surface by means of stereo digital image correlation (DIC). An infrared (IR) camera is synchronised and calibrated together with the DIC cameras, so that the temperature field can also be tracked on the deformed surface. This gives insights into coupled thermo-mechanical phenomena like self-heating due to plastic dissipation, enabling correct interpretation of the material response. This technique could prove equally suitable for cyclic loading and other classes of materials, when inhomogeneous strain fields and thermal effects are likely or expected to occur.