Hygrothermal Peformance Analysis Of 3D Textile Composites

3D textile polymer-matrix composite shows excellent mechanical performance,it is well accepted in the engineering field,especially in aircraft,trains etc.However,the hygrothermal environment during its service life will destruct its internal structure,thus reducing its mechanical performance.Therefore,this paper mainly did a research on the law of moisture absorption and the change of elastic modulus in the wet and humid environment.Firstly,this paper attempted to simulate the moisture uptake process of 3D woven composites by means of finite element method(FEM).Meso-scale geometric configurations for both surface region and interior region of 3D braided composite were constructed,and modifications of cross sections of fiber bundles in surface region were made to achieve the equivalent fiber volume fraction there.Then a mixed element model was proposed which can discretize 3D braided composite with uniform element mesh.Thus the difficulty of element discretization for 3D braided composite introduced by its complicated local braided architecture is avoided.Secondly,this paper also gave a theoretical model of the water weight gain of 3D braided composite materials.The diffusion equations of two-phase material moisture absorption were deduced firstly,then the moisture diffusion parameters of interior cell and surface cell were derived respectively using the steady moisture concentration gradient and equal moisture flux conditions under the circumstance of steady state diffusion,after that those parameters were applied to the proposed two-phase theoretical model.Finally,the theoretical and FEM results were compared with the test data,the results showed both of the theoretical model and the FEM results had good agreement with the test results.The 3D braided composite revealed a phenomenon of self-acceleration in the beginning of whole the moisture uptake process,the meso-scale parameters of 3D braided composite should be taken into consideration during the analysis of moisture uptake process.Finally,this paper assumed that the elastic modulus of the resin and wet concentration under the premise of linear correlation,the theoretical models for elastic modulus during the water uptake period of unidirectional composite and 3D woven composite were constructed.The curve of those models showed good agreement with the test results.