Simulation of single fiber pullout response with account of fiber morphology

A finite element model was developed at the single fiber length scale to predict the quasi-static pullout response of individual fibers from cementitious composites. The model accounts for energy dissipation through granular flow of the interfacial transition zone (ITZ) and matrix, plastic work in the fiber, and frictional dissipation at the fiber–ITZ interface. The considered fiber morphology was a triangular cross section that had been uniformly twisted along the fiber length. The model was calibrated to published experimental data for fiber pitches of 12.7 and 38.1 mm/revolution pulled from cement mortar with a 44-MPa unconfined compressive strength. The model was used to investigate slip-hardening behavior, tunneling of the cement mortar, in situ pullout behavior of helically twisted fibers at a crack plane, and provide an alternate explanation for the pullout response of twisted fibers from a 84-MPa unconfined compressive strength matrix containing silica fume. Calculations show that twisted fibers can provide up to 5 times the peak pullout force and 10 times the total work compared with straight fibers and infer work-hardening behavior during fiber pullout. The findings indicate that the tailoring of fiber morphology and control of constituent properties are important avenues for achieving significant improvements in the performance of fiber-reinforced cementitious composites.