Constitutive Modeling Of Woven Fabric Reinforced Thermoplastic Composites And Deformation Simulation Of Thermoforming-Injection Integrated Process

Compared to thermoset composites,continuous fiber reinforced thermoplastic composites(CFRTP)have higher toughness and impact resistance,better repairability and recyclability,making them becoming ideal new-generation structural materials for national strategic areas and pillar industries such as aerospace,deep sea vessels,automobiles,etc.Continuous fibers are typically arranged into fabrics to meet specific mechanical performance requirements under different service conditions.Woven fabric reinforced thermoplastic composites(WFRTP)use a woven structure composed of warp and weft yarns overlapping each other as the reinforcement,which is widely used due to its ability to maintain a relatively stable structure during the forming process.Thermoforming process is the main production process for manufacturing WFRTP.During the thermoforming process,the plastic flow of thermoplastic resin and shear deformation of the woven fabric interact with each other,making complex deformation behaviors of WFRTP.There is a lack of effective simulation methods to accurately predict the deformation behavior of WFRTP currently.This thesis investigated the deformation mechanism of WFRTP during the thermoforming process,and established the constitutive models to describe the deformation behaviors of WFRTP.Furthermore,this thesis analyzed the warpage deformation of thermoforming-injection integrated parts and established a simulation method to predict the warpage deformation.The specific work of this paper is as follows:The mechanical behaviours of woven fabric and its thermoplastic prepreg were systematically investigated based on self-designed fixtures and an experiment platform.The nonlinear in-plane shear deformation of woven fabric is due to the change in yarn motion,where the yarns undergo relative rotation,adjacent compression,and sliding during the deformation process.The in-plane shear deformation of molten-state prepreg is similar to those of woven fabric,where the thermoplastic resin slightly hinders the motion of yarns.The in-plane shear deformation capability of rubbery-state prepreg significantly decreases with decreasing temperature.The rubbery-state resin transfers loads between the yarns,exerting a strong hindrance effect on yarn movement.The nonlinear axial tensile deformation of woven fabric is due to the variation in yarn crimp.Additionally,there is a coupling effect between axial tensile deformation and in-plane shear deformation,where axial tensile deformation changes the yarn crimp and makes it more difficult for the in-plane shear deformation.The overlapping structure of warp and weft yarns in the woven fabric leads to the coupling interaction between axial tensile deformation and in-plane shear deformation in WFRTP.Therefore,a hypoelastic constitutive model was proposed to describe the deformation behavior of WFRTP during the molten-state thermoforming process,with particular attention to the coupling deformation characteristics.The model adopts an objective stress rate updated by yarn rotation to describe strong anisotropy deformation.It adopts a strain-dependent modulus to describe the strong nonlinear deformation and a correction factor to describe the tensile-shear coupling effect.The incorporation of the tensile-shear coupling effect improves the accuracy of shear angle prediction.The model’s average predicted error for the shear angle at measurement points of the double-arch part is25.1%,which is reduced by 44.7% compared to the initial model that does not consider the tensile-shear coupling effect.Furthermore,it has been observed that the movement of yarns in regions with significant shear deformation can increase the flow of molten resin,potentially leading to resin overflow.Conversely,in regions without shear deformation,the yarn structure remains stable,decreasing the degree of molten resin overflow.A hybrid lamination model based on the domain superposition technique was proposed to describe the deformation behavior of WFRTP during the rubbery-state thermoforming process,with particular attention to the hindering effect of resin’s elastoplastic deformation on in-plane shear deformation of woven fabric.The model considers the WFRTP as the laminate structure with woven fabric embedded in thermoplastic resin.It generates meshes for woven fabric and resin separately,and establishes a deformation compatibility relationship through node degree constraints.The coupled hypoelastic constitutive model was adapted to describe the anisotropic nonlinear deformation of woven fabric.The DSGZ phenomenological constitutive model was adapted to capture the effect of temperature on the elastoplastic deformation of thermoplastic resin.In a hemispherical thermoforming experiment,the model achieves a predicted shear angle precision of 96.2% at the measuring point.Additionally,the model’s predicted outlines of the parts under various initial yarn orientations show excellent agreement with experimental results.Furthermore,the predicted location of yarn axial stress concentration regions by the hybrid lamination model is aligned with the regions where the part experiences fracture failure.The reorientation of yarns during the thermoforming process causes local mechanical property variations in WFRTP,which affect the warpage deformation of thermoforminginjection integrated parts.Therefore,a simulation method for predicting warpage deformation for integrated parts was proposed.The simulation method obtains the yarn orientation and geometric shape of the deformed WFRTP through thermoforming simulation.Based on the predicted yarn orientation,non-uniform anisotropic mechanical properties are calculated and mapped onto the deformed geometry.The material properties of the WFRTP component are then incorporated into the injection molding simulation to compute the overall deformation of the integrated parts.Incorporating local performance variations caused by yarns reorientation effectively improves the deformation prediction accuracy of integrated parts.For instance,in a reinforced square box part with an initial yarn orientation of 30°/120°,the predicted error of vertical distance at the measurement point is reduced from 7.6% using uniform anisotropy to 3.7% using non-uniform anisotropy.