Study Of Mechanical Behavior And Damage Mechanism Of Ultra-high Performance Concrete Based On Meso-mechanics

This paper takes a mesoscopic perspective,regarding ultra-high performance concrete(UHPC)as a three-phase composite material consisting of cement mortar,steel fibers,and the interfacial transition zone between the two.A collision detection algorithm for different types of steel fibers was developed using a PYTHON script program.Subsequently,a UHPC mesoscopic numerical model was established.Through simulating the uniaxial compression of UHPC,the effects of steel fiber volume fraction,length,and type on the axial compressive performance and damage process of UHPC were studied,revealing the damage and failure mechanism of UHPC.The main work of this paper includes:(1)Simplifying the collision detection algorithm for the conventional circular cross-section steel fibers using PYTHON script language,which improves the efficiency of steel fiber placement.Additionally,a collision detection algorithm for hooked-end steel fibers was further proposed using quadratic optimization.An algorithm for milling-type steel fibers’ collision detection was proposed under the conditions of bounding box algorithm and separating axis theorem.This algorithm is also applicable to the collision detection of other arbitrarily shaped steel fibers.A microstructural numerical model for different types of steel fibers was established based on a random fiber model.(2)Various single-fiber pullout tests were conducted for different types of steel fibers.The bond strength between circular straight steel fibers(hooked-end steel fibers),copper-coated microfilament steel fibers,and milling-type steel fibers with UHPC was calculated based on the test results.Based on the failure mode,phenomena,and bond stress-normalized slip curve of the experiments,a pullout model applicable to different types of steel fibers was proposed.On the basis of the experimental research,a microstructural numerical model for the steel fiber pullout test was established using ABAQUS software.Under the conditions of the cohesive force-friction model describing the steel fiber bond slip,the numerical simulation of the steel fiber pullout test was performed.The results showed that the numerical simulation was in good agreement with the experimental results,verifying the accuracy of the bond slip parameters proposed in this paper.(3)Based on the reasonable bond slip property parameters between steel fibers and UHPC matrix,the microstructural numerical model of UHPC was simulated under uniaxial compression.By controlling the variables of steel fiber volume fraction,length,and type,the effects of these parameters on the axial compressive performance and damage process of UHPC were explored,and the damage and failure mechanism of UHPC under axial compression were revealed.