Multiscale analysis of compressive damage in 3D five-directional braided composites

At present, researchers have made significant progress in studying the mechanical properties of 3D braided composites. However, there are still deficiencies in the research on the failure mechanism, internal damage defects, and crack propagation distribution of 3D five-directional braided composites. For this purpose, a systematic experimental investigation was conducted on such materials with braiding angles ranging from 18° to 35°, including quasi-static compression tests, fracture morphology characterization by scanning electron microscopy (SEM), and 3D visualization reconstruction by CT scanning. The results showed that with the increase of braiding angle, the failure of specimens changed from brittle fracture to progressive damage accumulation under longitudinal compression, while braiding angle exhibited minimal impact on the failure mechanisms of materials under transverse compression. An increase in braiding angle generally facilitates the formation of pore defects and restricts crack propagation. However, an increase in the braiding angle from 30° to 35° leads to the opposite effect. Moreover, CT scanning could precisely depict the internal damage and crack propagation distribution within the composites. This capability is of great importance as it helps to reveal the failure mechanism of composites and provides a crucial data foundation for the analysis of pore defects of composites.