Analysis Of Molding Process Parameters And Typical High Temperature Mechanical Behavior Of C/PPS Composites

Compared with traditional thermosetting composites,thermoplastic composites have good heat resistance,high toughness,excellent creep resistance,high damage tolerance and good impact resistance.Therefore,high-performance thermoplastic composites have become the research hotspot for new aerospace materials now.The macroscopical experimental tests and the mesoscopic finite element unit model were used to study the mechanical properties and damage mechanisms of thermoplastic composites at different temperatures.A continuous carbon fiber fabric-reinforced thermoplastic polyphenylene sulfide(PPS)composite material was prepared by a hot-press curing process.The thermophysical properties of the thermoplastic PPS resin,such as melting temperature and viscosity,were analyzed by DSC,TGA and rheological tes ts.Various hot-press curing process parameters were given based on the experimental results.The molding temperature,forming pressure,holding time and cooling were investigated.The influence of the parameters and other parameters on the mechanical properties of the thermoplastic composites and the control mechanisms,and thus the best thermoplastic composite molding process parameters: molding temperature is 325°C,molding pressure is 1MPa,holding time is 30 min,the cooling method is natural pressure cooling.Basic mechanical experiments(tensile,compressive,bending and in-plane shear tests)at different temperatures are performed for thermoplastic composites,The influence of temperature on the mechanical properties and failure mechanism of thermoplastic composites was obtained.It was found that as the temperature increased,thermoplastic PPS resin softened,the matrix performance decreased,the fiber/matrix interfacial bond strength deteriorated and the interlaminar load transfer ability was weakened,which in turn led to the mechanical properties of the thermoplastic composites.The failure mode of the material under compression,bending and other loads gradually changed from brittle fracture to plastic obvious fiber buckling failure.Based on the effect of temperature on thermoplastic composites,the attenuation of material storage modulus is used as a useful indicator to measure the degradation of material properties.A thermodynamic model capable of predicting the mechanical properties of thermoplastic composites at different temperatures and loads is proposed.The model has a simple structure.The selection limit of the reference temperature is not obvious,and the forecast accuracy meets the design requirements.According to the structural characteristics of the thermoplastic composite C/PPS satin weave,a microscopic unit cell model was established.The macroscopic effective elastic constant of the thermoplastic composite material C/PPS was calculated by applying the periodic displacement boundary conditions,and the model prediction results were tested with the material at room temperature.The results are in good agreement.Based on this,using the method of constructing a neural network,macroscopic experimental results are used to infer the in-situ effective properties of the component materials at different temperatures.Through the microscopic unit cell model,the elastic constants of composites corresponding to the component material properties of different values are calculated,and the i nput and output vectors of the neural network are constructed.After the neural network is trained,a robust network is obtained,and finally measured by the input experiment.Performance parameters of thermoplastic composites at different temperatures to predict their material properties at high temperatures.Finally,according to the nonlinear behavior exhibited by thermoplastic composites,combining relevant flow laws and exponential hardening laws to describe the plastic strain evolution of thermoplastic composites,establishing the relationship between effective stress and plastic strain,and introducing damage variables based on the material's unloading stiffness degradation,considering the effect of temperature on material properties,a plastic-damage combined macroscopic nonlinear constitutive model is established.The constitutive model presented in this paper can accurately predict the stress-strain relationship of the C/PPS material under different temperatures,under off-axis tensile,compressive,and in-plane shear loads.When the model is embedded in the finite element subroutine,the constitutive model can predict the mechanical behavior of the complex geometries of thermoplastic composite C/PPS well.