Numerical modelling of the dynamic pull-out of steel fibers from cementitious materials

Abstract

Since fiber pull-out is the main reason for the toughness of fiber-reinforced cementitious composites, it is important to properly simulate this mechanism in dynamic models for this type of materials. Available experimental results show that the pull-out response of steel fibers embedded in concrete matrices exhibits sensitivity to the loading rate. This paper presents a model for the dynamic pull-out of fibers from cementitious composites. The model takes into account inertia effects and rate effects that influence the forces at the fiber-matrix interface, matrix micro cracking, mechanical anchorage and snubbing effects. The tangential stresses at the interface are calibrated based on experimental results obtained from pull-out tests of straight fibers performed at different loading rates, from quasi-static loading to impact loading, for different types of concrete matrix, including ultrahigh performance concrete (UHPC). The paper is complemented by the simulation of the pull-out of hooked end fibers at different loading rates and inclinations. The comparison with experimental results shows that the developed pull-out model is able to simulate the dynamic pull-out of steel fibers with different geometries and orientations from different types of concrete matrices. The inertia effects are negligible compared to the contribution of the other mechanisms to the pull-out response and to the effects due to the strain rate dependence of the fiber-matrix interface parameters.