| 3D multi-layer wraping braid composite was a new-type structure that based on original 3D braid composites. Compared with the original 3D braid composites, it has the common advantages as well as its own superiority, so it is an material worth profound investigation. In this thesis, investigations are implemented from several aspects below.firstly, braid craft and yarn direction are studied. The routine of 3D multi-layer wraping composite projected on the bottom plate is gotten. The yarn alignment in space in obtained, showing straightforwardly the space configuration. Based on the previous steps, representative volume cell for the structure-unit cell is built. Some essential coefficients are acquired, such as fiber volume fraction,braid angle, yarn filling factor and so on.Secondly, 3D multi-layer wraping composite is certified as an orthogonal material with the stiffness averaging method. By this method and the other Kregers' weighted average model stiffness properties is solved, predicting the 9 engineering elastic constants. Finite element model was also established to predict the engineering elastic constants. The two theoretical results were compared with the FEM, and the advantages and disadvantages were analyzed.Thirdly, using Abaqus/Explicit, dynamic explicit analysis was conducted, and stiffness reduction for the damaged elements was accomplished by the vectorized user-defined material(VUMAT)subroutine. The Mises stress criterion was used for the matrix as well as Puck criterion was used for the fiber bunch. The damage process of tension and compression is simulated, eventually the strength of the composites is gained.fourthly, 3D multi-layer wraping braid composites was molding by the advanced RTM technology,so the low-pore and less damage spicemen were gained. Experiments of the samples with better quality were completed. The predicted results agree well with the test data, analyzing the deviation reason,validating the rationality of this model in this thesis. |
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