A Study Of Creep Behavior Of Carbon Fiber Reinforced Polypropylene Composites

As new energy vehicles,civil aviation and other fields have put forward higher requirements for the lightweight performance of materials,composite materials have attracted more and more attention,and their application in the industry is more and more common.However,in the design and use of composite materials,the creep behavior of materials will cause excessive deformation,which will affect the stability of composite materials in the structure,and even cause fracture damage.This makes it extremely important to study the creep behavior of composite materials.In addition,as countries around the world cooperate to achieve the goal of "carbon neutrality",the composite industry is also actively exploring the recycling of carbon fiber and resin.Each year,tens of thousands of tons of carbon fiber are discarded during the production of carbon fiber composites.Most of the discarded carbon fiber is recycled in the form of staple fiber.In this study,the dumbbell sample of recycled carbon fiber reinforced polypropylene composite(rCF/PP)was prepared by injection molding process using recycled carbon fiber and polypropylene resin.The creep behavior of rCF/PP under different stresses and temperatures was studied to find the industrial direction for the reuse of recycled carbon fiber.Due to the low glass transition temperature of the polypropylene resin in the substrate,the creep deformation will be larger when it is used in load-bearing parts for a long time at room temperature.At present,there is still a large gap in the research of creep behavior of recycled carbon fiber reinforced polypropylene composites.In this paper,the creep behavior of rCF/PP was studied by uniaxial tensile creep test,creep acceleration test and finite element co-simulation,the Findley power law creep model and Burgers constitutive model were verified,and the main creep curve under reference temperature and reference stress based on the time-temperature-stress superposition principle was established.A finite element model containing fiber alignment information is established and the results are applied to predict the creep behavior of rCF/PP samples.The traditional creep test method was to conduct uniaxial tensile creep test on rCF/PP samples at room temperature.The tensile creep behavior of rCF/PP samples in real environment was studied,and the influence of stress level on the creep behavior was discussed.The Findley power law creep model and Burgers four-element model were used to fit the strain-time data.Two creep models were used to predict the creep behavior of rCF/PP.The research method of accelerated Creep test was to select small size rCF/PP sample to carry out short-term creep test under DMA Creep mode.The influence of stress and temperature on creep and creep recovery behavior was studied.The main creep curve of rCF/PP under reference temperature and stress conditions was established by using time-temperature superposition principle and time-stress superposition principle.Considering the complex fiber alignment results in injection molding rCF/PP,common finite element simulation methods are difficult to simulate the anisotropic material properties.In this study,mold flow analysis software Moldex3 D and injection molding mapping software Converse were used to grid the rCF/PP model,and the fiber alignment results and nonlinear material properties were given to the model,which were imported into Abaqus through FEA interface for co-simulation of tensile creep,and then compared with the uniaxial tensile creep test results.This method is used to predict creep behavior.The prediction results of the above three creep behavior prediction methods were summarized and compared,which provided a reference for establishing the creep behavior research process of short fiber reinforced thermoplastic composites.The uniaxial tensile creep test is showed that rCF/PP is a nonlinear viscoelastic material and its creep behavior is stress-dependent.High level stress can accelerate the creep of rCF/PP.DMA test is showed that rCF/PP has stress dependence and temperature dependence.The main creep curve with a good superposition degree cannot be obtained simply through the horizontal movement curve.In other words,the principle of time-temperature superposition and time-stress superposition cannot be directly applied to rCF/PP.The real fiber alignment in rCF/PP samples is simulated by Moldex3 D mode flow analysis.The simulation results of tensile creep are obtained by Abaqus,which proved to be in good agreement with the results of uniaxial tensile creep test.It is concluded that the finite element model could well predict the creep behavior of rCF/PP.