Macro synthetic fiber pullout behavior in short- and long-term tests

The creep phenomenon in fiber-reinforced composites is particularly important when synthetic macro fibers are used. In addition to the low modulus of elasticity, the polymers used in fibers have pronounced viscoelastic behavior even at room temperature, which can lead to changes in the cracking control over time. The long-term fiber pullout response also results from fiber and interface creep contributions. To understand the above phe-nomena, pullout tests with short-and long-term loads were conducted on three types of polymeric macro fibers subject to different levels of long-term loads (20, 30, 40 and 50%). The results of the pullout tests were strongly dependent on the fiber configuration, surface corrugation and modulus of elasticity. Macro fibers with crimped surfaces and higher modulus of elasticity achieved higher bond stresses and lower creep deformations. The Burgers model was applied and showed a good agreement with the experimental creep curves, therefore con-sisting of a promising alternative for modeling long-term behavior. Microtomography and scanning electron microscopy images showed that a large portion of the strain in tension, under sustained load, can be attributed to the creep of the fiber itself, thus making it challenging to estimate the creep of this type of composite, given the considerable variability of fiber configurations.