A phase-field framework for failure modeling of variable stiffness composite laminae

Three-dimensional (3D) printing of continuous fiber-reinforced composites (FRCs) and automated fiber placement (AFP) technology have enabled the fabrication of variable stiffness composites (VSCs), a kind of advanced composite materials reinforced by curvilinear fibers, which have been demonstrated with superior global mechanical properties. However, the fracture behaviors, an indispensable factor in the engineering structure design, of the VSC are still unclear due to a lack of research. To fill in the gap, the paper presents a multi-phase-field approach to perform the failure analyses of VSC laminae at mesoscale through which the VSC lamina is modeled as an anisotropic while nonhomogenous brittle material. The proposed model is validated against experimental results of fracture behaviors of single edge cracked and open-hole FRC laminae. Then a systematic investigation of the failure analyses of the pre-cracked and open-hole VSC laminae under different designs is performed. The results reveal that the propagations of cracks are always along with the fiber orientations in notched VSC laminae. In addition, a progressive failure mode demonstrated by the load–displacement curve can be amazingly observed in some designs. Moreover, the guidance in the design of VSCs with discontinuities is also provided based on the modeling results. Our presented fundamental insights in designing the novel fracture-resistant FRCs may promote the application of VSCs in automotive and aerospace structures.