Effect Of Fiber Drawing Characteristics Of The Resistance Of The Matrix Crack In Fiber Reinforced Cementitious Composites

The interaction between the matrix and the fiber is one of the most important factors which influence the mechanic properties of the cement composite. The interaction can be described by the pull-out properties of the fibers in matrix, In this thesis, the bridge action of the fibers on the crack propagation in matrix are discussed both by analytical and experimental methods. The main contents of this thesis are as follows:1. The process of the fiber pull-out from matrix is analyzed and two kinds of the pull-out model are established analytically. One model is based on the assumption of the shear-slid relationship and the other is based on the shear stress distribute area assumption, the analytical expressions of the pull out curves F - 5 are obtained; By extended the first kind pull-out model to the two end pull -out problem, the two end pull out curve F - 5 are obtained analytically.2. The crack propagation of the mode I crack with fiber bridge are discussed in the view of the stress intensity factor and power function near the tip of the crack, the bridging effect of the fiber on the critical condition of the crack propagation are analyzed and two critical model are established and discussed.3. A series experiments were designed to demonstrate the analytical discussion above. The first group of the experiments was to discuss influence of the volume ratio of the fibers in the crack area on the propagation of the crack; the second was to discuss influence of the intensity of the cement matrix on the propagation of the crack; and the last was to discuss the cyclic load on the propagation of the crack. The experiment results indicated that with the increase of the volume ratio of the fibers, the fibers can provide lager bridge force on the crack surface and so the critical external force will increase. For the samples subjected to cyclic load, the interface bond between the fiber and matrix are damaged and the bridge force decrease, as the result the external critical loads of the crack propagation were decreased. All the result demonstrated the relationship between the pull out property and the crack propagation in matrix qualitatively.