Deterioration of Fiber–Matrix Regime and Evaluation of Fiber Duct Damage during the Kinematic Pullout Process of Straight Steel Fibers in Cementitious Matrices

This paper presents a comprehensive study on how damage in fiber ducts could be reduced, and how the residual shear bond strength could be improved when straight steel fibers are pulled out kinematically from cementitious matrices. The shear-sliding mechanism of rigid material combined with elastic matrix was described using new elastoplastic recovery model. The problem of fiber–matrix regime deterioration was analyzed and resolved through three methods, theoretically using an analytical model, experimentally using pullout tests, and numerically using computer simulations. The various parameters controlling the behavior of the fictional bond strength were analyzed. The experimental results were validated by the numerical simulations, and the theoretical approaches using a calibration method. The derived equations were controlled by a deterioration coefficient determined empirically based on a given force–displacement curve. The results showed that long fibers exhibit slip-softening behavior, while shortening the embedment length boosts the slip-hardening behavior. Furthermore, based on the given dimensions of the studied fibers, the results showed that decreasing the fiber diameter by 83.3% increases the frictional shear bond strength by six times, and decreasing the embedment length by 45.2% increases the frictional shear bond strength by 91%. Finally, the results showed that decreasing the fiber aspect ratio by 45.3% increased the fiber duct resistance against damage and improved the frictional shear bond strength by 102.2%.