Effect Of Interfacial Mechanical Parameters On Twin Fibers Pullout Test Of Concrete Matrix

Interface between fiber and concrete matrix is the key path to transfer stress. Lot of concrete lose their function due to failure of interface. However, it is difficult to conduct numerical simulation to investigate influence of interface on failure mechanism of fiber concrete, because tiny size of the interface and very strong couple effect between each phases of fiber concrete, even those studies on twin fibers pulling out tests which consider heterogeneity of each phases.In this study, heterogeneity of each phases has been included based on micro scale models.2D and 3D numerical simulation on twin fiber concrete matrix has been conducted by using a commercial code named RFPA (Realistic Failure Process Analysis). Various complete load vs.displacement curves have been obtained by changing mechanical properties and size of the interface, moreover AE evolution and stress distribution have also been investigated. Thus, the failure, strengthening and toughening mechanism could be analyzed in details. The main content is listed as followings:(1) 2D and 3D numerical models of pull-out test on twin fibers concrete have been generated based on various interfacial strength. The effect of interfacial strength has, therefore,been studied. The results show that the interfacial strength has distinguish effect on the peak load (strength) and toughness of the models. The higher the interfacial strength is, the higher the peak load and toughness of models are. Furthermore, the increase of peak load of the model is typically linear to the increase of the interfacial strength. Finally, the interfacial strength has influence on the failure pattern and the distribution of shear stress.(2) 2D and 3D numerical models of pull-out test on twin fibers concrete have been generated based on various interfacial modulus. The effect of interfacial modulus has, therefore,been studied. The results show that the toughness and strength of models with low interfacial modulus are higher than those with high modulus. It is good to release the stress concentration and the stress transferring between the fiber and concrete matrix, when the interfacial modulus is low.(3) 2D and 3D numerical models of pull-out test on twin fibers concrete have been generated based on various steel fiber diameters. The effect of fiber diameters has also been studied. The study shows that the fiber diameter has influence on the failure pattern and the distribution of shear stress in 2D simulation. In 3D modelling, its effect on strength and toughness vs. volume ratio could be more distinguished. When fiber diameter increases, the model strength and toughness provided by unit volume of steel fibers decrease. In addition, the debond speed is also found has relation with the fiber diameter. The larger the diameter is, the higher the debond speed is,which means the failure could happen within less time.(4) 3D numerical models of pull-out test on twin fibers concrete have been generated based on various interfacial thickness. The effect of interfacial thickness has been studied. The study shows that increasing interfacial thickness to certain value will be beneficial to the model strength and toughness. When interface is more thick,it is good to transfer more stress via interfaces and the mean shear interfacial strength increases. Moreover, with thicker interface,both the damage in the interface and the debond between fibers could be postponed.