Flow-dependent fiber orientation distribution and its effect on the tensile behavior of ultra high performance cementitious composites

Abstract

In this dissertation, it was intended to understand the effect of the fiber orientation distribution on the tensile behavior of UHPCC and to estimate flow-dependent fiber orientation distribution and the corresponding tensile behavior of UHPCC. First, as a preceding research in order to predict the effect of the fiber orientation distribution on the tensile behavior of UHPCC, the pullout behavior of fiber in UHPCC was investigated. The fiber inclination angles considered in the pullout tests were $0\deg$, $15\deg$, $30\deg$, $45\deg$, and $60\deg$. From the pullout tests, it was observed that the largest peak load was obtained at an angle of $30\deg$ or $45\deg$, and the peak slip increased as the fibers were oriented at more inclined angles. The relation between fiber inclination to tensile load axis in pullout test and bond resistance was quantified, and a pullout behavior model of steel fiber in UHPCC was proposed considering fiber inclined angle. Then, the effect of the fiber orientation distribution on pre-cracking and post-cracking tensile behavior of UHPCC was investigated. Pre-cracking tensile behavior is expressed using the mechanism of elastic shear transfer between the matrix and the fiber in the composites. Meanwhile, in order to predict post-cracking behavior, a probability density function for the fiber orientation distribution across crack surface and a pullout model of steel fiber are considered. The effect of the fiber orientation distribution was found to be very small on pre-cracking behavior, but to be significant on post-cracking behavior of UHPCC. The predicted results were compared with the experimental results, and the comparison presented good agreement. The variation of the fiber orientation distribution along the flow of fluid was studied. In order to describe the rotational motion of a single fiber, Jeffery’s equation was adopted, in which the interaction among fibers is neglected. Two cases of flow patterns were considered; t...