Influence of realistic microscopic fiber misalignments on compressive damage mechanisms of 3D angle-interlock woven composites: In-situ measurements and numerical simulations

Stochastic fiber misalignments have been proven to have a significant impact on the compressive strength of traditional unidirectional laminates. However, these inherent manufacturing defects are rarely considered when dealing with 3D woven composites, due to the difficulty in characterizing the misalignment angles of individual fibers within all yarns. The current work provides the first in-situ measurements of fiber misalignments in 3D angle-interlock woven composites (3DAWCs) at the microscale, where the continuous fibers inside the warp, weft, and binder yarns are systematically examined using a high-resolution optical microscope. Statistical analysis reveals that the microscopic fiber misalignments follow a normal distribution, and the magnitude of the misalignment angle increases slightly with the degree of yarn fluctuation. Through a developed user subroutine, SDVINI, the obtained misalignment distributions are initialized in the corresponding yarns that belong to the constructed high-fidelity model. In comparison to the idealized one, the model introducing realistic fiber misalignments can effectively correct the overestimated predictions, and exhibits better agreement with the performed experiments. Furthermore, the influence of fiber misalignments on compressive damage mechanisms, particularly kinking failure, is also parametrically studied by incorporating different misalignment distributions.