Effect Of Embedment,Interfacial Modulus And Heterogeneity On Single Fiber Pull-out Test Of Concrete Matrix Under Dynamic Load

Interface is one of important component of steel fiber reinforced concrete（SFRC）.Normally,failure of the interface debonding occurs before damage of SFRC.In engineering practice,it is always seen that concrete structures are seriously damaged under dynamic load.Hence,it is of great research value to analyze the influence of physical and mechanical properties of the interface under dynamic load on the tensile performance of SFRC.At present,there are many studies on the dynamic mechanical properties of SFRC.However,only few detailed studies have been conducted on the effects of various phases on overall dynamic mechanical properties of SFRC under dynamic load.Since the interface dimension is very small,it is very difficult to analyze the interface performance under dynamic load,the study on the interface between steel fiber and concrete matrix in the dynamical field is even rarer.In this thesis,mechanical properties of three phases,i.e.steel fiber,interface and concrete matrix have been investigated in details.Numerical models of single fiber pull-out test under dynamic load have been created based on meso-level heterogeneity of material by using dynamic analysis software,named RFPA^2D（Realistic Failure Process Analysis）Dynamic Version.By changing the physical and mechanical properties of the interface in the model,complete curves of axial load vs.displacement of the SFRC specimens under dynamic load are obtained.Shear stress distribution at the interface is then analyzed.Bases on observations on acoustic emission（AE）characteristics,failure pattern and energy dissipation capacity of the specimens have been investigated for dynamic damage of different single fiber pull-put specimens under dynamic load.Main findings in this thesis are summarized as follows:1.Numerical models of single fiber pull-out test under dynamic load have been created with various embedding depth.The influence of embedding depth under dynamic load on single fiber pull-out test of SFRC has been studied.The results show that failure pattern and interfacial debonding performance under dynamic load are significantly different to each other with different embedding depth.When embedding depth increases,amount of damaged concrete cells and interface cells of specimen reduces.Residual load capacity of the specimen is relatively higher.The ability of the sample to resist the dynamic load is,therefore,enhanced.2.Numerical models of single fiber pull-out test under dynamic load have also been created based on various interfacial modulus.The influence of interfacial modulus under dynamic load on single fiber pull-out test of SFRC has been studied.The results show that amount of damaged cells of matrix is different to each other for different interfacial modulus,even during the same dynamic loading period.When elastic modulus of interface increases,failure pattern of the SFRC under dynamic load changes from strength failure（with steel fiber not pulled out）of steel fiber to debonding failure（with steel fiber pulled out）.3.Furthermore,numerical models of single fiber pull-out test under dynamic load have been created based on various interface heterogeneity.The influence of interface heterogeneity under dynamic load on single fiber pull-out test of SFRC has been studied.The results show that when the interfacial heterogeneity increases,brittleness of SFRC then increases.Specimens will fail in a shorter time.Energy required for failure energy and dissipation capacity of the specimen reduce.