Study On The Mechanical Behavior Of Three-dimensional Braided Composites Considering Structural Random Effect

Three-dimensional(3D)braided composites break through the concept of traditional composite laminates,and have great advantages and potential in improving the strength,impact resistance and damage tolerance between and within layers.However,in the actual manufacturing process of 3D braided composites,the structure of fiber bundle interweaving is complicated,and due to the impurities in the environment,the process implementation is not perfect and other factors,there are some defects in the final product,which brings great difficulty to the analysis of its mechanical behavior.Therefore,it is of great significance to correctly evaluate the structural strength,damage evolution law and material reliability of braided composites considering microscopic random effects,and to improve the practicability and reliability of braided composites in the aerospace field.Based on the stochastic theory,a theoretical calculation model of elastic constants of fiber bundles and 3D braided composites considering the random squeezing effect of yarns is established.One of the basic advantages of this model is that it is not necessary to accurately describe the waveform of the reinforcement when predicting the elastic properties.The only basic features as input data are the mean value of the random features of the fiber bundle and the standard deviation of the tangent vector of the fiber bundle path of the variable scale path,which is a random value describing the deviation of the reinforced path from the "perfect" path.Secondly,based on the theoretical model and finite element method,the effect of three random effects of yarn(random fiber path fluctuation,random contraction of fiber bundle section and random torsion of fiber bundle section)on the equivalent elastic constant of 3D braided composites was studied,and the sensitivity of braided Angle change to the random elastic response of materials was studied based on the random effect.Thirdly,the sensitivity of the elastic constants of 3D braided composites to the equivalent elastic constants of the materials was studied based on the effect of yarns’ microscopic random effect.The results show that the influence of microscopic random characteristic parameters on the stochastic equivalent elastic constants of 3D braided composites is closely related to the braided Angle and elastic properties of component materials.Finally,based on the influence of yarn microscopic random effect,the influence of structural random effect on the structural strength and stress distribution of 3D braided composites is studied.The results show that the microscopic random characteristic parameters of 3D braided composites have a certain influence on the structural strength,and the degree of influence of meso-random on the strength is also closely related to the braided Angle.