Characterization of steel fiber/cementitious matrix interfaces using a combination of fiber pullout and Moire interferometry techniques.

摘要

Fiber-reinforced cementitious matrix composites have been developed which provide enhanced toughness compared to the un-reinforced materials. The performance of these materials has been shown to be determined by the properties of the fiber/matrix interface: the interfacial fracture energy Gamma i and the interfacial sliding stress tau. Developing a complete understanding of the fracture behavior of these materials, including measurement of their interfacial properties, remains one of the key obstacles to developing useful, high-toughness cementitious composites.; A modified single fiber pullout test has been designed to study the fracture process of fiber reinforced cementitious materials. The test incorporates a crack-bridging fiber which accurately simulates the matrix cracking, crack deflection, and fiber debonding events which occur during failure of real composite materials. Using a suitable fracture mechanics debonding model, the interfacial fracture energies and sliding stresses have been calculated for composites incorporating steel fibers with cement paste and mortar matrices. Differences between the measured interfacial properties are associated with changes in the interfacial microstructure. Analysis of fiber unloading during debonding showed that the interfacial shear stress decreases with fiber/matrix sliding. Impedance spectroscopy was utilized to monitor the debonding process during the pullout experiment, showing that debonding occurs symmetrically with respect to the matrix crack in crack-bridging fibers.; The modified fiber pullout test was combined with Moire interferometry, allowing the simultaneous measurement of the fiber axial and interfacial shear stresses and the load vs. crack opening behavior. Together, this information provides a complete description of the fiber debonding and pullout process, including the progressive growth of the debond crack and the changes in shear stress along the debonded fiber. This observed debonding behavior is generally consistent with the assumptions of the selected fiber debonding model, with the exception of the observed decrease in shear stress due to fiber/matrix sliding.