Abstract
It is well known that fibers improve the performance of cementitious composites by acting as bridging ligaments in cracks. Such bridging behavior is often studied through fiber pullout tests. The relation between the pullout force vs. slip end displacement is characteristic of the fiber-matrix interface. However, such a relation varies significantly with the fiber inclination angle. In the current work, we establish a numerical model to simulate the entire pullout process by explicitly representing the fiber, matrix and the interface for arbitrary fiber orientations. Cohesive elements endorsed with mixed-mode fracture capacities are implemented to represent the bond-slip behavior at the interface. Contact elements with Coulomb’s friction are placed at the interface to simulate frictional contact. The bond-slip behavior is first calibrated through pull-out curves for fibers aligned with the loading direction, then validated against experimental results for steel fibers oriented at 30 and 60. Parametric studies are then performed to explore the influences of both material properties (fiber yield strength, matrix tensile strength, interfacial bond) and geometric factors (fiber diameter, embedment length and inclination angle) on the overall pullout behavior, in particular on the maximum pullout load. The proposed methodology provides the necessary pull-out curves for a fiber oriented at a given angle for multi-scale models to study fracture in fiber-reinforced cementitious materials. The novelty lies in its capacity to capture the entire pullout process for a fiber with an arbitrary inclination angle.
Highlights
Since conventional concrete tends to fail in a brittle manner under excessive loading, fibers are often added to improve its ductility and durability
Mesh sensitivity analysis is first conducted along the fiber transverse and debonded segments of the fibre occurs and the most superficial pieces of matrix longitudinal directions in order to determine the particular mesh to be employed for further studies
We have proposed a numerical model to explicitly reproduce the pullout behavior of a single fiber embedded within a cement-based matrix
Summary
Since conventional concrete tends to fail in a brittle manner under excessive loading, fibers are often added to improve its ductility and durability. The effectiveness of the given type of fibers, steel fibers in particular, is often assessed through a pullout test, in which the force required to pull a fiber out of the hardened concrete is measured. The transmission of this force is achieved through the interfacial bond, defined as the shear stress at the interface between the fiber and the surrounding matrix [7,11,12,13]. Naaman et al [12] pointed out that aligned fibers (i.e., load is applied at the fiber longitudinal direction) exhibit two types of shear bonds at the interface: elastic and frictional. When the elastic shear stress at the interface exceeds the bond strength of the interface, the bond becomes frictional in nature
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