A robust and predictive three-dimensional (3D) finite element (FE) model for evaluating the pullout behavior of steel fibers from a cementitious matrix

Abstract

Despite the extensive experimental and theoretical investigations on the pullout behavior of steel fibers from fiber-reinforced cementitious composites (FRCCs), the effects of the fiber clamping condition on the pullout behavior remain unclear. There is also a lack of rational assessment of the existing methods for evaluating the pullout behavior of steel fibers in FRCCs. This paper presents a simple, robust and predictive three-dimensional (3D) finite element (FE) model for elucidating these issues. Particularly, a modified Mohr-Coulomb (MMC) model was proposed to describe concrete spalling. A simple three-parameter cohesive-friction model was proposed to describe the fiber/matrix interfacial behavior. Having a low sensitivity to mesh size and a high meshing flexibility, the proposed FE model was computationally efficient. The robustness of the FE model was demonstrated by reproducing the experimental results from the literature covering both single-sided and double-sided pullout tests with a wide range of matrix strengths, fiber diameters and yield strengths, using only three physical fitting parameters (i.e., friction coefficient, confining pressure and cohesive strength). The numerical simulations showed that single-sided pullout tests overestimated the bond strength due to the unrealistic rigid-clamping conditions. Two-sided pullout tests with unequal fiber embedment lengths were preferable for resembling the action of fibers in cracked FRCCs. Traditional micromechanical models inappropriately evaluated the snubbing effect, as they predicted overly stiff bridging stress-crack opening (σ<inf>B</inf>−w) curves and overestimated the peak stress. A novel analytical model was proposed which provided comparably accurate predictions of the σ<inf>B</inf>−w curve with the FE simulations of two-sided pullout tests.