Research On The Damage Mechanism Of Triaxial Braided Composites Based On Multi-scale Model

Compared with the traditional laminates composites,braided composites are widely applied into vehicles,sports equipment and aerospace because of their higher damage tolerance and better energy absorption capability.The 2D triaxial braided composites(2DTBC)studied in this paper are one of the most popular braided composites.However,owning to their anisotropic and heterogeneous structures,the failure modes are quite complicated under different loads,such as fiber breakage,matrix cracking as well as interfacial delamination.Moreover,different failure modes can be coupled with each other.However,the failure behaviors mentioned above cannot be captured accurately by single scale models at present.Therefore,for the safe and efficient use of the composites,a multi-scale finite element progressive damage model needs to be established to study the damage mechanism deeply.Based on continuous damage mechanics(CDM),the micro and meso progressive damage model are built on the fiber/matrix scale and the tows architecture scale respectively.The initiation and evolution of the damage of 2DTBC under tension and compression loads are studied in detail based on the multi-scale progressive damage model.Firstly,the micro RUC model with hexagonal arrays of fibers is set up.The initial failure of fiber and matrix is determined by the maximum strain criterion and Stassi criterion.Combining with the progressive damage evolution criterion based on the fracture energy,the damage morphology of the micro RUC under different loads is analyzed.The stiffness and strength of the fiber tows are obtained as well.Compared with the mechanical parameters calculated by the existing theoretical formulas,the mechanical parameters of the fiber tows obtained by the micro damage model are very close to them.Then,the mechanical parameters of the fiber tows are transferred to the meso model,and the finite element mechanical model of 2DTBC with high-fidelity is established.The failure criterion and stiffness reduction scheme like the matrix in the micro RUC are also adopted for the matrix in the meso model.The initial damage of fiber tows is characterized by 3D Hashin criterion,and the progressive damage process is simulated according to the stiffness reduction scheme based on fracture energy.Besides,the cohesive connection with bi-linear traction-separation law is employed to capture the onset and propagation of interface failure.Finally,the progressive damage process of 2DTBC under tensile and compressive loads is studied,and the specific damage modes are also identified.The influence of interface performance and the size of the model on the mechanical properties of the composites are also analyzed in detail.Results show that the stress-strain curves and damage morphology of 2DTBC obtained from numerical simulation are in good agreement with experimental data.Moreover,the interface has a weak influence on the tensile mechanical properties of the material,and the different size of model has a great influence on the transverse mechanical properties of the composites,while has little effect on the axial mechanical properties.