Mesoscopic Simulation Study Of The Influence Of Spacing And Matrix Strength Of Twin Fibers Pull-out Test Under Dynamic Load

As one kind of high performance multi-phase composite material,fiber reinforced concrete?FRC?has been widely used in the field of construction engineering in China.In engineering practice,in addition to the quasi-static load which changes slowly,the FRC structure is inevitably subjected to dynamic loads such as earthquake,explosion and external impact.Due to complex composition of FRC structure,there are many factors affecting the reduction of its mechanical properties.As one extremely important micro-structure of FRC,the interface is a bridge of stress transmission between fiber and concrete matrix.It is also the area where material initial failure appears.The interface properties affect significantly the overall macro-properties and damage mechanism of material.It is,therefore,of great significance to study the damage mechanism and interface mechanical behavior of fiber reinforced concrete under dynamic loading.The static mechanical properties of fiber reinforced concrete are inherently complicated,and stress field distribution,strain deformation and fracture process are more complicated when considering dynamic load.Moreover,due to extremely small interface size,it is particularly difficult to characterize the interface structure and its mechanical properties.That is one possible reason that the research results of the mechanical behavior of fiber-reinforced concrete interface under dynamic load are rare to be obtained.In this paper,by considing the complexity of FRC dynamic failure,A microscopic dynamic numerical model of twin fibers pull-out test composed of cement mortar,aggregate,steel fiber and interface has been established by using RFPA^2D-Dynamic?Realistic Failure Process Analysis?dynamic analysis software based on the meso-heterogeneity of concrete material and strong coupling effect between fibers.The complete process from micro-cracks initiation,propagation to crack penetration of twin fibers pull-out specimen under dynamic loading has been simulated.The dynamic failure mechanism,interface mechanical behavior and acoustic emission behavior of twin fibers pull-out specimen under dynamic loading have been analyzed from the mesoscopic level.The main contents are as follows:?1?With variables of loading peak and rate,dynamic numerical model of twin fibers pull-out test under interface control was established.The influence of loading peak and loading rate under dynamic load on twin fibers pull-out test has been studied.The results show that the dynamic failure pattern of the twin fibers pull-out test specimen has the correlation of loading peak and loading rate.The loading peak and rate have great influence on the interface crack propagation and interface shear stress transmission.When both loading peak and rate increase,the rate of interface crack propagation and interface shear stress transmission increase.The loading peak and rate differ in the magnitude of the acoustic emission peaks produced by the pull-out specimen.?2?With variable of twin fibers spacing,the dynamic numerical model has been established and the mechanical properties of twin fibers pull-out specimen was studied.The results show that the fiber spacing has great effect on failure pattern of specimens.Furthermore,both peak load and relative toughness show a tendency of increasing first and then decreasing along with increase of the twin fiber spacing.When the spacing is changed less or larger then the optimised one,both peak load and toughness decrease,and the test specimen shows more obvious brittle behavior.?3?With variable of matrix strength,the dynamic numerical model of twin fibers pull-out of concrete and cement mortar under interface control has been established.The mechanical properties of twin fibers pull-out specimen was then studied.The results show that the strength of the matrix has great influence on failure pattern of the specimen.As the strength of the matrix increases,the failure pattern of the pull-out specimen was transformed.The aggregate has alsogreat influence on the propagation of stress wave and failure pattern.More cracks and severer damage have been identifed in cement mortar matrix than in concrete matrix.