Meso-mechanics Influence On Spacing And Embedded Length Of Twin Fibers Pullout Test

Fiber reinforced concrete has now been widely used in civil engineering. Adding different kinds of fibers could efficiently enhance the overall mechanical properties of concrete. The interface is formed when concrete is hydrating with fibers and it has completely different mechanical properties to concrete and fiber, thus it will cause a series of complicated physical and chemical reactions. The mechanical property of interface has great effect on the macro mechanical properties. There are many methods for characterizing the mechanical behavior of interface, among these methods, single fiber pull out test is the most common used one. However, single fiber pull out test could only characterize one specimen but twin fibers pull out test is the foundation of multi-fibers pull out test, which has great significance in studying the failure mechanism of multi-fiber reinforced concrete. In most of pull out theories and numerical study, interaction of cement, aggregate, fibers are not considered. In addition, interface are based on material homogeneity and axisymmetric.In this paper, 2D numerical models are generated basing on meso-level material heterogeneity by using RFPA2 D. All components like cement, aggregate, fibers and interface are simulated in the models. Furthermore, 3D models are generated by using ANSYS and RFPA3 D. Parallel computation approach has also been involved in the study. The mechanical properties of twin fibers pull out models by changing twin fibers spacing and embedment depth under interface control have been studied. Moreover, the mechanical properties of single fiber pull out models by changing interface heterogeneity have been studied either. On the other hand, physics experiments of twin bars pull out test have also been conducted and corresponding load-displacement curves are obtained.The major content in this paper are summarized as followings:(1) With variable of twin fibers spacing, both 2D and 3D numerical models are generated. The mechanical properties of the pullout test are analyzed. The results show that the change of twin fibers spacing could affect the peak load of the models. When the spacing increases, the peak load increases either. The toughness of the specimens increases first then decreases with the increasing of the spacing. Furthermore, the variation of the twin fibers spacing has great impact on failure process and stress distribution.(2) With variable of twin fibers embedded depth, both 2D and 3D models are established and the mechanical properties are studied. The results indicate that the change of the embedded depth has great influence on the damage process of the matrix. The acoustic emission(AE) accumulation and the toughness index increase either. In addition, the change of embedment depth also has great effect on the failure process and stress distribution.(3) Twin steel bars pullout experiments have also been conducted. Load-displacement curves are obtained for subsequent theoretical research.(4) With variable of interface heterogeneity, both 2D and 3D numerical models of single fiber pullout specimens are established. The study shows that, with the increase of the heterogeneity, the peak load and the AE accumulation increase simultaneously. Furthermore, with low heterogeneity, the specimen shows good toughness and with high heterogeneity, it shows brittleness in performance. Furthermore, with low interface heterogeneity, the interface could efficiently buffer stress concentration and regulate stress redistribution.