Single Pullout Test And Theoretical Analysis Of Tapered Steel Fiber

In this paper, tapered steel fibers with different angles were designed modelled on the micro wedge structure of nacre. The ends of the fibers with tapered angle were buried into cement motar and a series of tests were performed. A theoretical model was established to simulate steel fiber taper end be pulled out from the cement mortar matrix in stable pullout state.In this work, steel fibers that buried into cement mortar were pulled out from the matrix at static load. The steel fibers in static experiment has various tapered angles and they were classified into chemical and no chemical based on the surface of the fiber was treated or untreated（reflect the matrix and fiber friction coefficient to a certain extent）. We pulled the tapered fiber out from the cement motar matrix by using the MTS universal testing machine and designed fixture at different speeds（2.5 mm/min, 25 mm/min, 250 mm/min） and get the maximum pullout force and work of pullout force. The results show that the taper angle of steel fiber have a positive effect on the maximum pullout force; There in no consistent effect of the pullout speed of all kinds of angle steel fiber on the maximum pullout forc e; the equivalent bond strength of small angle steel fiber increases with the increase of the angle, but the equivalent bond strength of bigger angle steel fiber is smaller because of the matrix failure; the maximum pullout force of untreated fibers is bigger than that of treated fibers in overall; the work of pullout force of 2 ° fiber is the biggest at all test speed and whether the surface of the fiber were treated or untreated have no effect on the work of pullout force; when the specimen failure, the pullout displacement of the treated fibers is bigger than that of untreated ones.Drop hammer impact instrument was used in this p aper to perform dynamic impact pullout tests of 2°and 5°steel fibers from cement motar matrix. The effect of tapered angle and load rate on pullout test results were studied. The test result shows that the tapered angle of steel fiber have effect on the ma ximum pullout force and it associated with the impact pullout rate. On the whole, with the increase of impact velocity, the maximum pullout force has obvious increasing trend. The angle and the work of pullout force have no definite correlation. Overall, t he increase of impact pullout velocity will make the equivalent bond strength of steel fiber and matrix a corresponding increase. The tapered angle of steel fiber have effect on the equivalent bond strength of steel fiber and matrix.A theoretical model was established in this paper to simulate steel fiber taper end be pulled out from the cement mortar matrix in stable pullout state and we calculated the pullout force F and F_θ>0/ F_θ=0 about the parameters of the taper part of the fiber. Analysis results show that the matrix strength ζc, the tapered angle, and the coefficient of friction f have obvious effect on the pullout force F and F_θ>0/ F_θ=0. but the modulu of matrix E, hardening shrinkage strain of the cement mortar matrix εs have no unconspicuous effect on them. Partial result of the model can well correspond with the test results.