Research On Compression And Impact Resistance Of Open-hole Composite Laminates Reinforced By Z-pin

Composite material has been widely used in aerospace field due to its excellent properties and has become an important structural material.Due to the need of connection and other design,the composite structure often needs to be perforated,thus serious stress concentration phenomenon appears around the hole edge,which complicates the damage accumulation and reduces the strength of the perforated structure.As a typical interlayer enhancement technology,Z-pin enhancement technology can be used to improve interlayer performance and alleviate the occurrence of hole edge damage.This paper presents an experimental study into the loading capacity of open-hole composite laminates reinforced by Z-pin and discuss the effects of different parameters.ABAQUS finite element analysis method was applied to modeling and analyzing the enhancement mechanism of Z-pin.(1)The forming process of the open-hole composite laminates reinforced by Z-pin was optimized and the perforated samples were prepared.An experimental study was carried out to investigate the enhancing effect of Z-pin for the compressive capacity of open-hole laminates.The influence of different volume contents of Z-pin implantation and different hole diameters has been studied.The forming quality of open-hole laminates can be significantly improved.The experimental results show that Z-pin implantation can significantly improve the compression bearing capacity of the open-hole laminates.When the volume content of Z-pin is 3%,its compression strength increases by 23.06% at the maximum.The comparison of the experimental results with different diameters shows that when the volume content of Z-pin was lower than 1.5%,the 10 mm diameter sample had the most significant enhancement effect,and when the volume content of Z-pin was higher than 2%,the 6mm diameter sample had the best enhancement effect.(2)Finite element model was established to analyze the influencing mechanism of Z-pin for the open-hole composite laminates.The strengthening effect of composite matrix and Z-pin was simulated based on progressive damage analysis and cohesive element method.The Z-pin enhancement region was simulated by cohesive unit layer,and the damage change of element layer was approximately regarded as the bearing change of Z-pin.The numerical results show that the compression damage extends from the edge of the hole to both sides,and the lamination in the center of the laminate is the first to be damaged,among which the cohesive elements in the 6th and 10 th layers are the first to be damaged.The simulation results are in good agreement with the test results.(3)The post-impact compression test was carried out on the open-hole composite laminates.The experimental results show that 6.36 J and 12.72 J impact energy were applied to the open-hole laminates respectively,the maximum impact contact force was increased by 12.35% and 1.50% due to Z-pin,the total energy absorbed in the impact process was reduced by 10.54% and 1.25%,the area of layered damage after impact was reduced by 8.76% and 24.83%,and the residual bearing capacity of the structure was increased by 17.44% and 21.44%,respectively.Under the influence of the two kinds of impact forces,laminates with Z-pin spread all over the plane have the maximum impact force increased by 5.48% and 1.13%,the total energy absorption reduced by 19.94% and 9.81%,the area of stratified damage reduced by 25.41% and 30.88%,and the residual compression strength after impact increased by 18.73% and 11.72%,respectively.Z-pin has a more obvious enhancement effect on the compression process,and all Z-pin implantation has a better damage improvement effect.