The effect of temperature on mechanical properties and failure behaviour of hybrid yarn textile-reinforced thermoplastics

Multi-axially reinforced textile composites with thermoplastic matrix are investigated under thermomechanical loading conditions. Two groups of composites made of glass fibre/polypropylene hybrid yarn are chosen as examples: a novel 3-D textile-reinforced composite with multi-layered flat bed weft-knitted reinforcement and a composite with woven reinforcement. The presented study concentrates on determining the mechanical properties depending on temperature and investigating the complex failure behaviour and its provoking phenomenological damage processes like void growth and inter fibre damage at different temperatures by the use of optical microscopy and visual observations of specimens. With the focus on automotive applications, the elasticity constants and strength values have been determined in the range from −40 °C up to 80 °C using uniaxial tensile and compressive tests. As a result, the basic properties like stiffnesses and strengths are mathematically described depending on the temperature. Additionally, dynamic-mechanical analysis have been used to identify the glass transition range of the thermoplastic matrix system and to find correlation to the temperature-dependent mechanical properties.