Multi-scale Study Of Compression After Impact Damage Of CFR Plain Woven Materials

Compared with traditional composite materials,CFR(carbon fiber reinforced)plain weave materials have very good in-plane properties,as well as higher specific modulus and specific strength.However,CFR plain woven materials will inevitably suffer low-energy impacts during use.For example,when maintenance workers are repairing machines,accidental drops of maintenance tools,etc.are all low-energy impacts.The laminate structure is affected by the impact.Internal damages such as delamination damage,fiber fracture,and matrix cracking often occur,which seriously weaken the damage tolerance and load-bearing capacity of CFR plain woven materials.At present,it is difficult for the traditional single macroscopic model to describe the failure behavior described above accurately and in detail.Therefore,in order to evaluate the damage tolerance of the structure,this paper adopts a multi-scale method(micro-scale,meso-scale and macro-scale)to analyze the CFR plain weave.The compression performance of the woven material after impact was calculated numerically and verified by experiments.First,establish the micro-fiber bundle model and meso-unit cell model of the CFR plain weave material,apply periodic boundary conditions,damage initiation criteria and stiffness degradation criteria to it,and calculate the mechanics of the micro-fiber bundle and meso-cell model The performance parameters are then calculated based on the progressive homogenization method to calculate the equivalent mechanical parameters of the 0° and 90° single layers,and the established progressive homogenization subcell model is expanded into a macroscopic CFR plain woven material laminate.The results show that the longitudinal tensile and compressive mechanical properties of micro fiber bundles are determined by fiber and matrix,while the transverse and shear mechanical properties are mainly determined by matrix.Under the longitudinal tensile load,the damage of meso unit cell first appears on the zonal fiber bundle,while under the longitudinal compressive load,the damage of meso unit cell first appears on the meridional fiber bundle,and finally fails due to the fracture and collapse of the meridional fiber bundle.Secondly,the laminated board expanded from the progressive homogenization model is used to build an integrated finite element model of low-velocity impact(LVI)and compression after impact(CAI).Bring the calculated equivalent performance parameters of 0° and 90° single layer into the macro model of the CFR plain woven material board.On this basis,the three-dimensional Hashin failure criterion is used to simulate the initial damage of the laminate,using continuous The damage mechanics model is used to simulate the damage evolution of the laminate and the cohesion model is used to simulate the interlayer damage,and the low-velocity impact and compression after impact numerical calculations are performed on the laminate.Finally,based on the integrated finite element model of low velocity impact and post impact compression established above,and combined with the post impact compression test of CFR plain woven material,the correctness of the multi-scale method of progressive homogenization is verified.The results show that the simulation results of CFR plain woven material under low velocity impact and compression after impact are in good agreement with the experimental results.With the increase of impact energy,the impact force and impact damage area of laminates increase in turn,and the impact front surface changes from no damage to slight damage,and finally cross damage.However,the damage on the back of impact develops from the initial cross shaped damage to the final cross shaped convex crack,and the damage on the back of impact is greater than that on the front;However,the CAI behavior is on the contrary.The compression load and the compression damage area are negatively correlated with the impact energy,which decreases with the increase of impact energy.The compression damage starts from the impact center,and finally extends to the two edges of the specimen.The impact front laminate cracks from the central area,and the impact back bulges with a small number of cracks;The impact side is crumpled,and obvious fiber fracture can be seen.The residual compressive strength of laminates decreases nonlinearly with the increase of impact energy.