Finite Element and Experimental İnvestigation of the İnclined Pull-Out Behavior of Hooked-End Steel Fibers From Carbon Nanotube-Reinforced Ultra-High Performance Concrete

Abstract

This research investigates, both numerically and experimentally, the combined effects of carbon nanotube (CNT) and inclination on the pull-out performance of hooked-end steel fibers embedded in CNT-reinforced ultra-high performance concrete (UHPC). For numerical simulation, the finite element method (FEM) was employed using ABAQUS software, with modeling implemented based on cohesive zone theory (CZM). The mechanical properties of the CNT-reinforced UHPC, along with the CZM parameters, were derived from experimental testing across a range of CNT weight percentages (0 %, 0.1 %, 0.2 %, 0.4 %, and 0.6 %). These experimental tests included inclined pull-out tests of both straight and hooked-end steel fibers from UHPC specimens incorporating the aforementioned CNT concentrations. Following validation of the FEM results, a parametric study was conducted to estimate the influence of inclination angle and CNT content on the pull-out response, including peak pull-out force, slip at peak force, pull-out energy, and the extent of matrix spalling observed in each configuration. Results indicate that the inclusion of CNTs enhances the fiber-matrix bond, leading to improved pull-out resistance.