Research On Thermoforming Of Thermoplastic Carbon Fiber Woven Composites

Lightweight automobile is the current trend of the automotive industry.Materials processing technology innovation is the key to automotive light weighting.One direction of lightweight automobile is via materials lightweight,such as by using carbon fiber composites as an alternative for traditional steel material.Carbon fiber reinforced plastic(CFRP)composites have been extensively used in aerospace,wind power and defense and other fields.However,high manufacturing costs severely restricted them in high-volume applications such as in the automobile industry.In recent years,the decline in the cost of carbon fiber and increase production bring hope for introducing carbon fiber composites into the automotive industry.Combing thermoplastic carbon fiber woven composites with thermoforming technology makes it possible for carbon-fiber composites to adapt high-volume,low-cost,high-efficiency production of automotive industry.But different from steel materials,thermoforming of components with complex surface by using carbon fiber composites shows large deformation,anisotropic and multi-field coupling phenomenon,making the existing theoretical basis,equipment and processing technology for metal stamping cannot be directly transplanted into carbon fiber composite forming.Through experimental tests and theoretical analysis,building numerical model for carbon fiber composites thermoforming,investigating the deformation mechanism and mechanical behavior of carbon fiber woven composites in forming,obtaining the effects of structure factor,matrix materials and process parameters on thermoforming,identifying typical defects and their characteristics and influencing factors,and thus developing carbon fiber woven composite thermoforming theory to provide theoretical and experimental basis for reliable forming of carbon fiber composite components with complex surface,is currently an urgent need to accelerate carbon fiber composite materials in the automotive lightweight applications.Tensile and picture-frame testing fixtures are designed to measure tensile and shear properties of carbon fiber woven material.The tensile and shearing behaviors of a plain weave carbon fiber are obtained from uniaxial tensile,bias extension andshearing tests.In order to characterize the mechanical behavior of carbon fiber woven composites in forming,an anisotropic hyperelastic constitutive material model is proposed based on continuum mechanics theory.The strain energy function is resolved into a shearing strain energy due to angle variation between the two fiber yarns and a tensile strain energy from the warp and weft yarn tensions.Without considering the case of unloading,the energy required for forming the carbon fiber woven composite can be approximately equivalent to the strain energy.Meanwhile,by fitting the aforementioned tensile and shear testing data,the material parameters in the proposed constitutive model can be obtained,whereby specific expression is required for engineering applications of the model.On the commercial CAE software platform ABAQUS,the developed material model is successfully implemented by using the custom routine module UANISOHYPER_INV for the numerical forming simulation of carbon fiber woven composites.Taking a component with double-curvature surfaces as experimental subject,experiments and numerical simulation on the draping of dry woven carbon fabrics over the corresponding double-curvature mold are carried out.The shearing angle distribution and deformed boundary profile are recorded from comparison.The effects of original fiber angle set-up and lay-up on the formability are investigated.Comparisons between experimental data and numerical simulations results indicate that the proposed hyperelastic constitutive equation can properly describe woven composites’ nonlinear anisotropic behavior under forming with large deformation.In order to achieve high-volume,low-cost manufacturing of composite components,by combining thermoplastics grains with plain woven carbon fabric,a thermo-forming method is proposed for forming composite parts which have double curvatures and complex shape in one step,to achieve prospect application of composites reinforced by fiber in the Auto Industry.A layered thermoplastic grains with carbon woven fabrics are heated in the proposed thermo-forming process,and then moved it quickly to a preheated mould for thermo-forming,and cooled down to form the CFRP experimental part.Various thermoplastics including Polyamide 6(PA6),Polypropylene(PP)and Acrylonitrile Butadiene Styrene(ABS)are used as matrix materials.It is demonstrated that high quality parts can be achieved with the proposed forming process,and defects are controllable.The experiment results show that the rheological characteristics of thermoplastic resin,the fixed method of mould,the yarn orientation of the composite blank are very important factors in the thermo-stamping of the thermoplastic carbon woven fabric composites.With the proposed process,it is feasible to implement the high-volume and low-cost manufacturing of fiber reinforced composite parts.Finally,according to specific deformation characteristics of woven composite inthe tensile and picture frame tests,and combining with the developed hyperelastic constitutive model,three indicators including shear lock angle,deformation boundary and temperature sensitivity for evaluating the formability carbon fiber woven composites are proposed,thus providing a reference for material selection and robust processing parameter setup in the forming of carbon fiber woven composites.