Preparation And Mechanical Properties Of Polyimide Fiber/Carbon Fiber Hybrid Composites

Carbon fiber itself not only has low density,extraordinary tensile strength,extremely high modulus and great chemical resistance,but also its composite materials are used in aerospace,marine,wind power blades,transportation,sports and leisure and other fields.There is greater potential for development in the future.However,the characteristics of high brittleness and poor toughness make carbon fiber composite materials relatively poor in impact resistance,resulting in a certain degree of damage inside the material when faced with impact,and the residual strength will be seriously reduced,limiting its wider application in various fields.Polyimide(PI)fibers have outstanding mechanical properties,high temperature resistance,UV radiation resistance and other characteristics,as well as good toughness and ductility,which make PI fiber composites have good impact resistance,but their tensile strength and stiffness are relatively lower.To this end,this paper aims to improve the impact resistance of carbon fiber composites,mixes carbon fibers and PI fibers in different forms,and uses the hybrid synergistic effect to improve the comprehensive properties of the composites.The main research contents include:PI fiber and carbon fiber prepreg were prepared by wet method,the thickness of single layer was 0.125 mm,14 different hybrid structures were designed by interlayer hybrid method,and PI fiber/carbon fiber hybrid composites were prepared by molding.The impact response and damage mechanism of hybrid composites were explored through drop hammer impact test and post-impact compression test,and the effects of the proportion of two kinds of fibers and the structure of the layer on the low-velocity impact property of the sample was studied.As can be seen from the results,when the content of PI fiber in the composites increased,the absorbed energy increased,the damage resistance was enhanced,and the damage area became smaller.When changing the layup order of the two fibers,the energy absorption effect of the composite with PI fibers on the surface was better than that of the composite with carbon fibers on the surface.Among them,the composite material with the PI fiber on both sides and the carbon fiber in the middle(H2)has the largest absorbed energy,and the composite material with the carbon fiber on the surface and the PI fiber on the bottom with the smallest damage area(H4),followed by H2.The residual compressive strength of the PI fiber/carbon fiber hybrid composite shows a positive hybrid effect.When the ratio of PI fiber to carbon fiber in the sample is 1:1,the positive hybrid effect reaches the maximum,and the PI fiber surface have stronger residual compressive strength than carbon fiber surface,and the residual compressive strength of C-H2 composite with PI fiber on both sides and carbon fiber in the middle is the highest.Comparing different hybrid ratios and layering sequences,the effects of PI fiber/carbon fiber hybrid composites on their mechanical properties were studied.The study found that as the proportion of carbon fibers in the composite increased,the tensile strength and modulus of the composite material showed an upward trend,but it was a negative confounding effect.When the ratio of PI fiber to carbon fiber is kept constant,the more uniform the distribution of the two fibers,the higher the tensile strength and modulus of the composite.With the increase of carbon fiber content,the flexural strength,modulus and shear strength of composites also showed an upward trend.The flexural properties of composite materials are mainly related to the fibers on the compression side.When the compression side is carbon fibers,the flexural strength and flexural modulus are higher.The law of shear performance is that when the carbon fiber is located on the compression surface,the shear strength of the composite is higher than that of the sample with the PI fiber located on the compression surface,and the more the number of interfaces between the fiber layers,the lower the shear strength of the composite.The failure mechanism of the samples is mainly as follows: the carbon fiber composite material is brittle fracture,the PI fiber composite material exhibits explosive ductile fracture,and the main cause of failure is that brittle fracture and ductile fracture happened at the same time,correspondingly the damage is not stronger.In addition,the exist of PI can partly stop the propagation of cracks so that raise the toughness of the composites.