Characterization Of Tensile Properties Of Carbon Fiber/polypropylene Composites

Composite materials have excellent mechanical properties,such as high tensile strength,bending strength and impact strength,which make the composite materials have a wide range of applications in various fields.Carbon fiber has the characteristics of light weight,high strength and high modulus,so it is often used in the composite system based on resin,metal,ceramic,cement,etc.In recent years,more and more attention has been paid to the study of carbon fiber reinforced polymer composites.It is of great significance to characterize the mechanical properties of carbon fiber reinforced polymer composites in a more detailed and in-depth way to understand their strengthening mechanism.The mechanical behavior and damage mechanism of two kinds of polypropylene composites containing carbon fiber series were studied by experiments,finite element method and theory.In this paper,a series of tensile samples of carbon fiber reinforced polypropylene composites were designed and prepared,and their mechanical properties were characterized by experiments.The effects of orientation and lengthdiameter ratio of carbon fiber on tensile strength of composites and the mechanism of interface damage were investigated numerically by finite element method.Combined with Mori-Tanaka model theory,the equivalent modulus of the composite was characterized.The results achieved are as follows:(1)A series of carbon fiber filling mass fraction,two lengths and adding maleic anhydride coupling agent carbon fiber/polypropylene composite splines were designed and prepared by melt blending process,and the tensile mechanical properties were measured,characterizing the effects of different carbon fiber mass fraction on the strength and elastic modulus of the composite.The results showed that the strengthening effect of 5-20% carbon fiber on polypropylene was 40.9%-43.2%.The effectiveness of maleic anhydride as a coupling agent to improve the binding properties of the interface was verified.The compatibilizer increased the strength by 5.6% and 7.8% when the filling amount was 5%and 10%,respectively.By exploring the reasons for the differences in mechanical properties of carbon fiber composites of two lengths,it was found that the strength of short carbon fiber with length of 6mm was lower than that of carbon fiber powder,which was due to the uneven mixing caused by its fracture during processing.Microstructure observation shows that the strengthening mechanism of carbon fiber is achieved by preventing the crack propagation in the matrix.(2)A three-dimensional(3D)finite element model of carbon fiber/polypropylene composite was established,and the effects of carbon fiber content,length-diameter ratio and arrangement direction on mechanical properties of carbon fiber/polypropylene composite were obtained through numerical simulation.The strength and modulus of the simulated composites are consistent with the experimental trend,and increase with the increase of the mass fraction of carbon fiber.The loadbearing stress difference of fibers in different directions is large,and the strengthening effect of fibers deteriorates as the Angle from the loading direction increases.Larger length-diameter ratio of carbon fiber has better reinforcement effect.Through the analysis of stress evolution,the damage and failure process of the two-phase interface of composite materials were characterized.(3)Based on the Mori-Tanaka meso-mechanical model theory,the equivalent modulus of the carbon fiber reinforced polypropylene composite was characterized and compared with the experimental results.Based on the catastrophic damage model and the simulation results,the damage failure rate of the two-phase interface conforms to the power law of 0.5.