Preparation And Mechanical Property Of Isotropic Carbon Fiber Reinforced Plastic Composites

In recent years,many countries all over the world have paid great attention to environmental pollution and automobile emissions,and put forward higher requirements for automobile manufacturing.Thus,the light-weighting strategie by the selection and design of car body composites has become research hotspots.At present,carbon fiber reinforced polymer(CFRP)is one of the key automotive lightweight materials.CFRP as an advanced composite material of car body,has many advantages,such as: light weight,high strength,excellent fatigue resistance,corrosion resistance and easy processing,can effectively reduce fuel consumption and the exhaust emissions of car as well as increase the mileage range of new energy vehicles.However,the high manufacturing cost,complicated production process and low recycling utilization rate of CFRP's have been the greatest obstacles to its widespread application in vehicles.The present industrial applications of CFRP normally uses two-dimensional woven carbon fiber cloth or unidirectional carbon fiber as reinforcing main body.However,the woven carbon fiber cloth/polymer composite is hard to use in fabrication of components with the complex curved surface due to the great in-plane shear deformation or even wrinkling and other defects occur,resulting in their composites' larger anisotropy and dispersion in mechanical properties.It is difficult to repair as an anisotropic composite for the car body application.In order to solve the problem that the anisotropic mechanical properties of the CFRPs prepared from unidirectional carbon fibers and two-dimensional woven carbon fiber clothes,the non-woven carbon fiber cloth and the carbon fiber with fixed length were selected as CFRP reinforcement.The CFRP composites with isotropic macro-mechanics were prepared by using the vacuum hot pressing process.This process,utilizing the isotropic distribution characteristics of the non-woven carbon fiber cloth and the fixed length carbon fiber to solve the anisotropic disadvantage of CFRP,not only saves the cost of the carbon fiber knitting,but also provides a more flexible method for the design of composite material.In addition,the effects of different fiber volume fractions on the tensile and flexural strength of the composites and the relationship of the two fiber reinforcements and the composites mechanical isotropic characteristic were investigated by adjusting fiber volume fractions in CFRP composites.The mechanical performance test results of the fixed-length carbon fiber/vinyl resin thermosetting composites showed that the addition of fixed-length carbon fibers with a length of 30 mm could significantly increase the tensile and bending strength of their thermosetting composites.With the increase of fiber content,the tensile and flexural strength and isotropic characteristics of the composites increase first and then decrease.With the fiber fraction in composites increasing to 25vol% and 30vol%,the tensile strength and flexural strength reach to 141.4 and 549.0MPa,respectively.In comparison with the CFRP composite with 15vol% carbon fiber,their mechanical properties increased by 112.8% and 129.6%,respectively.By analyzing the fracture morphology of the composite,the fracture characteristics of the fixed-length fiber-reinforced vinyl resin composite show a brittle fracture,and its failure models are matrix cracking and deformation,fiber debonding and fracture,and interlayer crack extension.The thermoplastic CFRP composite were also prepared from the non-woven fabric carbon fiber with surface density of 60g/m2 and nylon 6 resin by a vacuum hot pressing process,showing that the mechanical properties of the resin matrix have been enhanced greatly.The tensile and flexural strength of the composites increase rapidly with the increase of the fiber volume fraction.The mechanical test results demonstrate that the tensile strength and bending strength reach to the maximum value of 127.6 and 144.4MPa with 25vol% and 30vol% carbon fiber fractions,respectively.It could be seen that when the fiber volume fraction of the non-woven carbon fiber in CFRP is the same as that of the fixed-length fiber/vinyl resin system,the bending strength of former is only one quarter of the latter.The obvious differentia in the bending strength of the two CFRP composites may have close relation with the layer structure of the non-woven carbon fiber cloth in composite.The tensile strength of non-woven carbon fiber reinforced vinyl resin thermosetting composites the fiber fraction was 25vol% reaches to the optimal value,which increases by 167.5% in comparison with the composite with 15vol% fiber fraction.The dispersion coefficient of tensile strength of this composite is the lowest,suggesting that composite possesses stable mechanical property which can be contributed to the good infiltration of non-woven carbon fiber cloth in the resin.In addition,the tensile strength differentia in various directions of the composites prepared by non-woven carbon fiber reinforced vinyl resin is very small.It indicates the CFRP composites prepared from non-woven carbon fiber cloth effectively avoidedthe mechanic anisotropy of the traditional CFRP composite reinforced by two dimensional woven carbon fiber cloth.