Analysis Of Low Velocity Impact Properties Of Basalt Fiber Composites Considering Strain Rate Effect

Basalt fiber reinforced composites are considered as a promising new type of composites with high strength,high modulus,high fracture toughness,corrosion resistance and flame retardancy,which have great potential in aerospace and automotive applications.The braided fiber structure can improve the interlaminar and intralaminar strength of the fiber composite and the delamination resistance of the fiber composite.The obvious strain rate effect exists in fiber composites under dynamic loading.The strain rate sensitivity of composites varies due to their different properties.Low-speed impact can cause certain damage to the interior of composites,such as matrix cracking,fiber breakage,etc.For the low-speed impact simulation of composites,the quasi-static performance parameters of materials are used,and the effect of strain rate effect on the performance of composites is not considered,which makes the simulation results inaccurate.Therefore,the establishment of constitutive model considering strain rate effect is very important to improve the accuracy of low-speed impact simulation results.In order to study the influence of strain rate effect on low-speed impact properties of basalt fiber reinforced composites,samples of basalt fiber reinforced composites laminates were prepared,and quasi-static and dynamic tensile and shear tests were carried out to obtain the basic mechanical properties of the materials.The effect of strain rate on low-speed impact properties of basalt fiber composite was analyzed.The three-dimensional progressive damage constitutive model related to strain rate was established and the effects of impact energy,material thickness and ply angle on low-speed impact performance with and without strain rate were analyzed.In order to further analyze the evolution process of tensile and compressive damage of laminates under low-speed impact,a cell model at micro-scale is established,and the tensile and compressive simulation considering strain rate effect is carried out,and the damage evolution process is analyzed.The specific research content and research results are as follows:（1）The samples of basalt fiber composite were prepared,and the quasi-static tensile and shear tests,dynamic tensile and shear tests and low-speed impact tests were carried out to obtain the performance parameters and low-speed impact load-time curves of the material at different strain rates.When the strain rate increases from 0.0003s^-1 to 200s^-1,the tensile strength of the basalt fiber composite increases from 305MPa to 563MPa and the shear strength increases from 58MPa to 140MPa,which proves that the basalt fiber composite is sensitive to the strain rate.Meanwhile,the strain rate correction coefficients in different directions are obtained for subsequent simulation studies.（2）A constitutive model related to strain rate is established.Considering in-plane shear failure and inter-laminar failure,an improved three-dimensional Hashin failure criterion is established.The criterion includes fiber tension and compression failure in the warp and weft directions,in-plane shear failure and delamination failure;linear stiffness degradation program based on fracture toughness is chosen,and the modulus and strength are updated through the strain rate correction factor.The above-mentioned strain rate related constitutive model is compiled into a VUMAT subroutine and embedded in Abaqus for debugging.（3）Low-velocity impact performance of laminates is analyzed considering the effect of strain rate.A low-speed impact simulation model considering strain rate effect is established.Compared with the test results,it is found that the strain rate-dependent constitutive model can greatly improve the simulation accuracy,and the validity of the strain rate-dependent constitutive model is verified.The low-velocity impact under different conditions is simulated to analyze the effect of strain rate on the low-velocity impact performance of basalt fiber composites.The study found that as the increase of impact energy and laminate thickness,the strain rate sensitivity of basalt fiber composites increases.The strain rate sensitivity of basalt fiber composite under low-speed impact decreases with decreasing fiber ply angle The impact damage of the laminate is mainly the fiber compression damage on the impact surface,the fiber tensile damage on the back surface,and the delamination damage is mainly distributed inside the laminate.The in-plane shear damage will be distributed by±45°with the change of the principal stress direction,and will change with the change of the fiber layer angle.（4）Meso-damage considering the effect of strain rate is analyzed.A meso-scale unit cell model is established,and the unit cell model is subjected to tensile and compression simulation analysis under different strain rates.The validity and accuracy of the unit cell model considering the strain rate effect are contrasted and verified by comparing the simulation results with the experimental results.On this bases,the damage evolution of the unit cell under tensile and compressive loads is analyzed.Stress concentration occurs at the interweaving position of warp yarn and weft yarn with tensile load,which leads to serious matrix crack,and the fiber bundle also shows tensile fracture at the interweaving position.Under the compressive load,the compression failure of the matrix is serious,but the damage of the fiber bundle is not obvious.