PULLOUT OF INCLINED FLEXIBLE FIBER IN CEMENTITIOUS COMPOSITE

The performance of fiber-reinforced composites is strongly dependent o n the debonding/pullout behavior of the fibers. In cementitious compos ites, fibers are usually distributed in a quasi-random manner. It is t herefore important to study the pullout of fibers that are inclined to a crack. For flexible fibers, a simple model of a String passing over a frictional pulley has been developed to describe inclined fiber pul lout. The existing model is based on experimental results obtained fro m specimens with initially bent fibers. To evaluate the validity of th e experimental results and the model, pullout tests are carried out wi th polypropylene fibers using (1) specimens with initially straight fi bers; and (2) specimens with initially bent fibers. Significant differ ences are found between the two sets of results. Since the pullout beh avior of initially straight fibers is more representative of that in r eal composites, a new model for flexible fiber pullout is developed. B y considering (1) the increase of both interfacial friction and snubbi ng factor with sliding; and (2) spalling of matrix at fiber exit point in the new model, excellent fitting of the experimental results can b e obtained.