Finite Element Simulation For Hybrid Fiber Strain Hardening Cementitious Composites

PVA fiber reinforced cementitious composite(PVA-ECC)is a kind of unique ultra-high ductility fiber reinforced cementitious composite featuring tensile strain hardening behavior,of which with tensile strength superior than 5 MPa,and with the tensile strain generally of 3% to 5%.However,the elastic modulus of PVA fiber is lower compared with cement matrix,thus fiber rupture occurs when the strength of matrix is high,and bridging effect of PVA fiber may be negatively influenced.According to the published researches,applying steel fiber into PVA-ECC can greatly enhance the ductile and strength of the material.At current stage,the research on PVA-steel-ECC focused on the experimental research,although the experiments were time and labor consuming,and finite element simulation and practical application of ECC are inadequate.This paper adopts finite element model to study the mechanical properties under uniaxial compression,four-point bending and drop weight tests.The main research contents and results of this paper are as follows:(1)A random delivery process of hybrid fiber by using the Monte Carlo method is established.This paper develops the algorithm for the entity fiber’s 3D random distribution in three dimensional space using MATLAB program.The model 3D linear hybrid fiber obtained from MATLAB program is adopted in ABAQUS finite element simulation model of PVA-steel-ECC.The hybrid fiber is modeled as T3D2 element with different angles and failure modes.According to different angles,and whether it is pullout or rupture,the constitutive relationship uses a fiber-matrix joint constitutive model based on the single fiber pull-out load-displacement curve under the influence of angle,embedment depth,failure modes,snubbing effect and matrix spalling effect.The matrix is modeled as C3D8 R,and the constitutive relationship adopts the Damage Plastic Model.Utilization of the Embed command to combine the hybrid fiber with the matrix to establish a finite element model of the hybrid fiber ECC.(2)Using the hybrid fiber ECC finite element model to simulate the static mechanical properties of materials in uniaxial compression and four-point bending tests.The effectiveness of the model is verified by comparison with the previous experimental results of the research group.The effects of the parameters including volume blending ratio,mixing ratio and matrix cracking strength on the mechanical properties of the material are studied.In the uniaxial compression simulation,the incorporation of steelfibers and PVA fibers improved the toughness of ECC.With the proportion of steel fibers increases,the compressive strength and peak strain of ECC both show an increasing trend,and the increase in the amount of PVA fibers increases the ECC compression toughness index.In the four-point bending simulation,with the increase of the PVA fibers,the bending toughness index of ECC increases,and steel fibers improves the cracking load and flexural strength.When the two reach a certain ratio,ECC has high strength and toughness at the same time.Properly reducing the cracking strength of the matrix helps to improve the toughness of the hybrid fiber ECC and achieve strain hardening performance.(3)Using the hybrid fiber ECC finite element model to simulate the dynamic bending performance of the material under the drop weight impact test.The effectiveness of the model is verified by comparison with the previous experimental results of the research group.The effects of parameters such as volume blending ratio,mixing ratio,matrix cracking strength and strain rate on the dynamic flexural properties of the material are also studied.The study found that as the steel fibers added increases,the strength of the test piece increases accordingly,but at the same time,it reduces the toughness and the energy absorption of the material.Choosing the appropriate cracking strength of the matrix can better take advantage of the material’s multi-slit cracking and has better energy absorption performance under impact.As the strain rate increases,the peak force and energy of the hybrid fiber ECC under impact increase accordingly,the dynamic bending strength increases,and the material exhibits a significant strain rate effect.