Fiber distribution evaluation using digital image processing and its effect on tensile behavior of fiber reinforced cement composites

Abstract

This thesis presents a technique for evaluating the fiber distribution of a fiber-reinforced composite; it also investigates how the fiber distribution affects the tensile behavior of PVA-ECC and SFR-UHSC. The proposed evaluation technique is composed of stepwise tasks. First, the fiber images detected by a prototype thresholding algorithm are classified into five types by a watershed segmentation algorithm and an artificial neural network. Next, any aggregate fiber images, that is, misdetected fiber images, are detected correctly by means of the watershed segmentation algorithm and morphological reconstruction. Test results confirm that the fiber detection performance was enhanced and that the dispersion coefficient and orientation were calculated accurately. The developed evaluation technique was used to investigate how the fiber distribution affects the tensile behavior of PVA-ECC and SFR-UHSC. For the PVA-ECC, a fiber bridging constitutive law that quantitatively considers the distribution of fiber orientation was derived, and a fiber distribution analysis was conducted on four specimens with different mix proportions. After that, image analysis was used to obtain fiber bridging curves from the distribution of fiber orientation, and these curves were compared with those obtained from the assumption of a two-dimensional and three-dimensional distribution of the fiber orientation. Furthermore, the uniaxial tensile behavior of the ECC was analyzed by comparing the experimental test results with the simulation results based on the fiber bridging curves and micromechanical parameters. The comparison and simulation results confirm that the uniaxial tensile behavior can be approximately predicted by using the proposed method with image analysis of the fiber distribution characteristics. For the SFR-UHSC, flexural tests were conducted on specimens manufactured with two different placing directions, and measurements were taken of the flexural behaviors, includi...