In this paper, the effect of interface properties on the compressive failure behavior of 3D woven composites (3DWC) is investigated by incorporating a micromechanics-based multiscale damage model (MMDM). The correlation between the mesoscopic stress of yarns and microscopic stress of constituents is established by defining a stress amplification factor. With the microscopic stresses, the fiber breakage and matrix failure can be separately evaluated at the microscale, without assuming the yarns as transversely isotropic homogeneous materials. Especially, the interfacial debonding between yarns and matrix is also a dominant damage mode within 3DWC. Given that there is still a lack of studies on the influence of interfacial properties on the compressive failure behavior of 3DWC, it is meaningful to perform numerical parametric studies to reveal how the interface properties contribute to the damage mechanisms of 3DWC under compressions. The predicted results indicate that with the increase of interface strengths and fracture toughness, the compressive resistance of 3DWC can be significantly improved, resulting in higher strength and failure strain. Additionally, the studied 3DWCs with weak, medium and strong interfaces exhibit different damage development processes.

In this paper, a reliable progressive fatigue damage model (PFDM) for predicting the fatigue life of composite laminates is proposed by combining the normalized fatigue life model, nonlinear residual degradation models and fatigue-improved Puck criterion. To balance the accuracy of life predictions and computational efficiency, an adaptive cyclic jump algorithm is developed and implemented within the PFDM. The sensitivity of life prediction to cyclic jump parameter has been greatly reduced by correlating the cyclic jump with the increment time and viscous coefficient. Therefore, the cyclic jump parameter can be arbitrarily selected within a relatively large range to obtain convergent results. When incorporating the adaptive cyclic jump algorithm, there is no need to define a standard for determining the material failure in numerical calculations, which effectively eliminates an artificially induced uncertainty in life predictions. Two sets of experiments are conducted to validate the proposed PFDM. The numerical predictions including static failure strength and fatigue life correlate reasonably well with the available experimental data.

A novel micromechanics-based multiscale progressive damage model, employing minimal material parameters, is proposed in this paper to simulate the compressive failure behaviours of 3D woven composites (3DWC). The highly realistic constructions of microscopic and mesoscopic representative volume cells are accomplished, and a set of strain amplification factor is employed to bridge the meso-scale and micro-scale numerical calculations. Considering that the multiple failure mechanisms of 3DWC under compression are all caused by the matrix failure from the microscopic perspective, a new method incorporating the micromechanics of failure (MMF) theory and 3D kinking model is developed to identify the micro matrix failure associated with the kinking of yarns, inter-fiber fracture and pure matrix failure. As a result, only the matrix parameters are required for the failure simulation of 3DWC, eliminating the necessity of using other material parameters such as the fracture toughness and failure strengths of fiber yarns, which are generally difficult to accurately obtain through experiments. The newly proposed damage model is numerically integrated into ABAQUS with a user-defined subroutine UMAT. The numerical predictions and the experimental results exhibit good agreement, verifying the feasibility and accuracy of the novel damage model.