A Novel Modeling Strategy Of The Multi-scale Structure And The Mechanical Properties Of 3D Braided Composites

Three-dimensional(3D)braided composite materials are widely used as structural components in aerospace structures due to their excellent stiffness,high strength,excellent impact resistance and high delimitation resistance.With the continuous development of the braid processes and molding technology,the three-dimensional braided composite materials have demonstrated unique advantages in integrated molding and large-scale automated weaving.The premise of the widespread using of 3D braided composite structural parts is to accurately predict and analyze their mechanical properties.But the 3D four-directional braided composites have a complex internal structure,which brings certain challenges to predict their mechanical properties and damage modes.In this paper,by analyzing the movement trajectory of the yarn carrier during the weaving process,the spatial yarn layout is explored.And based on the reasonable assumption of the micro-scale,a multi-scale modeling strategy of three-dimensional four-directional braided composite is established.Based on periodic boundary conditions and homogenization theory,a finite element prediction model is obtained.After that,a surrogate model is proposed as an accurate and computationally inexpensive alternative to predict the mechanical properties of 3D four-directional braided composites.First,based on the structural characteristics of the 3D four-directional braided composite material,through reasonable assumptions,a micro-scale model of the fiber bundle is constructed.And by analyzing the movement trajectory of the yarn carrier in the weaving process,a mesoscopic model which can characterize the internal structure of the three-dimensional four-directional braided composite material is obtained.Due to the complex structure,the multi-scale models are discretized by the tetrahedral elements.In order to ensure the continuity of the displacement and traction at boundary surfaces of the RVEs,the periodic boundary conditions(PBCs)are used to perform the different loads on RVEs.To predict the effective elastic properties of 3D braided composites,a homogenization-based approach is developed to compute the overall stress components of the micro-scale and meso-scale RVEs.A finite element model that can accurately predict the mechanical properties of the three-dimensional four-way braided composite material is established.Secondly,a platform of 3D four-directional braided composite tensile test is built.And the elastic modulus and force-displacement curve obtained by the test are discussed.Meanwhile,the macroscopic fracture morphology of the test piece is analyzed to determine the macroscopic destruction mode.Finally,three braiding parameters(internal braiding angle,fiber volume fraction and short semi-axis of fiber bundle cross-section)are selected as variables of the surrogate model.And the parameter domain is determined in combination with the limitations of the existing braiding process.Within the varying ranges of these design parameters,the Latin Hypercube Sampling(LHS)is used to populate the training points to construct the surrogate models.Subsequently,the surrogate models of the elastic properties have been reconstructed using Diffuse Approximation in this work.The reliability of the surrogate models is verified by comparing the errors between the surrogate models and the experimental results.Moreover,for a more detailed analysis of the inaccuracy of the surrogate model,the inaccuracy between the surrogate model prediction and finite element results are argued.Based on the constructed surrogate model,the effects of three parameters on the elastic properties are discussed in detail.