Research on Constitutive Modeling for Plain Weave Fabric considering Coupling Effcts

Author:Yao Yuan

Supervisor:peng xiong qi

Database:Doctor

Degree Year:2018

Download:12

Pages:112

Size:5032K

Keyword:

In the forming process of weave fabric reinforced composite,the weave fabric reinforcement becomes a three-dimensional geometry from a two-dimensional plane,which shows nonlinear large deformation and strong anisotropy.The shear deformation of weave fabrics can affect impregnating effect and fiber content,and the orientation of fiber can influence the mechanical properties of the formed composite part after curing.Therefore,more accurate material constitutive models are needed,which can provide an important theoretical basis and practical value for optimizing the forming process and improving the prediction accuracy of mechanical properties of weave fabric reinforced composite parts.Although the biaxial-tension and tension-shear couplings of weave fabrics have been observed in experiments,most constitutive models often ignore coupling effects for simplicity.Thus,in this dissertation biaxial-tension coupling and tension-shear coupling,and their effects on prediction results in stamping simulation of weave fabric reinforcements are systematically studied.The main contents of this paper are as following:By using biaxial tensile testing results and based on continuum mechanics,a nonlinear anisotropic hyperelastic constitutive model considering biaxial-tension coupling is developed for plain weave fabrics.The strain energy function is decomposed into two parts to represent tensile energy including biaxial tensile coupling effect and pure shearing energy from relative rotation between warp and weft yarns.The method of determining the material parameters in the strain energy density function is given in details.The proposed coupled model is combined with the finite element software ABAQUS/Explicit by developing a user material subroutine vuanisohyper_inv.Then biaxial tensions under different stretch ratios are simulated.Numerical results are compared with corresponding experimental data for model validation,which shows the biaxial-tension coupling model can describe the nonlinear large deformation,strong anisotropy and the biaxial-tension coupling behaviors of weave fabric.Next the coupled and uncoupled models are separately applied to simulate a double-dome forming.The effect of biaxial tension coupling is analyzed by changing blank holder force and directions of fiber yarns.The comparative analysis shows that the biaxial-tension coupling model is more sensitive to the blank holder force which is an important process parameter in the stamping process.On the other hand,compared with uncoupled model,the results from the coupled model show that the shear deformation in the edge of the flange is lower and in the center area of the bottom of the double-dome part is higher.Based on the picture frame testing results with different uniaxial and even biaxial tension states,a constitutive model considering tension-shear coupling effect is developed for plain weave fabrics.The strain energy function is decomposed into two parts to represent tensile energy without biaxial-tension coupling effect and shearing energy from relative rotation between warp and weft yarns under different combined biaxial tension mode.The proposed coupling model is applied to simulate shear deformations under different combined biaxial tension mode,which shows the tension-shear coupling model can describe the tension-shear coupling behavior.Finally,the tension-shear coupled model and uncoupled model are separately employed for studying the forming processes with two geometric punches and three directions of weave fabrics.In each case,comparison is made between the coupled model and the uncoupled model,and the effects of tension-shear coupling are investigated.Numerical results demonstrate that the tension-shear coupling effect changes the rules of fiber reorientation during forming simulation process,which makes shear deformation tend to be uniform and reduces the local shear deformation concentration.Experiments of tetrahedron stamping for 0°/90° and ±45° plain weave fabrics are carried out.A coupled model simultaneously considering biaxial-tension and tension-shear couplings and the uncoupled model are separately applied to simulate the tetrahedron stamping.Then,the predicted boundary contour,distribution of shear angle,maximum shear angle and its position from the two models are compared with experimental data.Considering the simplicity of calculation,the accuracy of numerical results of hemisphere and double-dome stamping from the uncoupled model can still be accepted in engineering applications.However,when it comes to the forming of a tetrahedron with complex shape and sharp angle,the constitutive model considering tension-tension and tension-shear coupling effects is more suitable.The coupled model has important theoretical significance and practical value for optimizing the forming process and improving the prediction accuracy of mechanical properties of composite parts.