Research on tensile properties and size effect of 3D four-directional braided composites

By the macroscopic tensile tests of the 3D four-directional braided composites, the failure pattern and fracture morphology of specimens with different geometric sizes have been observed. It is obtained that the different failure mechanisms and the material properties are relevant to the geometric sizes of samples under tensile states. The elastic properties of the braided composites are obtained by volume average method. The variation of shear modulus and Poisson ratio is obtained as well. It is shown that the elastic modulus increases with the increase of number of interior cells. The predicted results are in agreement with the experimental results. The results may provide experimental basis for further study on strength prediction and the establishment of strength criterion for 3D four-directional braided composites.