5 - Textile fiber composites: Testing and mechanical behavior

Abstract

Mechanical properties of textile-reinforced concrete (TRC) materials such as strength, stiffness, and ductility are determined through standard or novel tests conducted under uniaxial or multiaxial conditions. By documenting the nature of cracking and damage evolution, the mechanisms that contribute to enhanced ductility in composites can be studied. This is achieved through closed-loop procedures to detect the incipient failure as the load is being applied and control the test accordingly, such that a constant rate of deformation is applied. Strain-hardening behavior is a characteristic response in TRC materials and is attributed to the gradual decrease of sample stiffness as parallel microcracking takes place. Load-carrying capacity increases with an increase in strain; however, widening of cracks in a tensile stress field results in delamination and fiber pullout modes of damage. The interpretation of the stress–strain curve thus obtained is not straightforward because it is influenced significantly by the specimen size, geometry, control mode of test and loading setup. Moreover, the deformation is not homogenous but is localized within a narrow zone that undergoes progressive damage and cracking. The strain-hardening response demonstrates the behavior of the specimen in terms of its ductility and energy-absorption capacity and parameters that contribute to it. A series of mechanical properties tests developed address tension, flexure, compression, pullout, drop-weight impact, and high-speed tension. Characteristic material responses obtained include elastic properties, stiffness, toughness, stress–strain curves, fracture toughness, ultimate tensile strength, crack width, crack spacing, and moment-curvature relationship.