Research On Modeling Of Micro-uncertainty And Elastic Parameter Identification Of Braided Composite

Braided composites have better out-of-plane stiffness,strength and toughness compared with traditional laminates.Preformed parts are interwoven by yarns which consisted of fibers.Uncertainty of yarn path is caused by warp tightening and high pressure resin flow in production process.The mechanical properties of macro-structure are influenced by the random geometry of micro-structure.The key to solve the problem is to obtain accurate elastic parameters and establish models with uncertainties.The main contents of this paper are as follows:Firstly,the secondary development function of large-scale finite element analysis software is used to establish the RVE model of braided composite materials quickly,the equivalent elastic parameters are obtained by imposing periodic displacement boundary conditions on the model.Extended model is obtained by reflecting the RVE.Homogenization model is established by the size and equivalent elastic parameters.The objective function is constructed by residuals between the above two models.The more accurate equivalent elastic constants are obtained by referring process of parameter identification.Simulation model conforming to dynamic characteristics is established.Secondly,elastic parameters are obtained from responses of static and dynamic test based on sensitivity analysis method.Orthotropic plate and beam are studied.The relative sensitivities of elastic parameters to modes of plates with different sizes are analyzed.The multi-stage parameter identification of the near square plate verifies the dimensional effect of E₁₁ and G₁₂ with high relative sensitivity were identified accurately according to the measured modal data.In the aspect of identification based on static response data,The relative sensitivity fields of elastic parameters to the response of strain and deflection at all measuring points are analyzed.The error between calculation and experiment is reduced by optimizing algorithm.Accurate elastic constants are achieved.Finally,identification interface is designed under App Designer platform.Finally,micro-uncertainty parameterized models of two woven structures are established respectively.At first,three-dimensional coordinates of axes of warp and weft are obtained by numerical calculation with MATLAB.The height and spacing are perturbed so as to change in a certain range.Two-dimensional and 2.5-dimensional uncertainty models are established by programming.The load boundary conditions are applied to the meso-model to predict the equivalent thermoelastic parameters.Statistical quantities of thermo-elastic parameters are obtained by a large number of models.The effect of yarn path uncertainty on the mechanical properties of braided composites is studied.