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.

连续纤维增强复合材料 (FRC) 的三维 (3D) 打印和自动纤维铺放 (AFP) 技术使可变刚度复合材料 (VSC) 的制造成为可能，这是一种由曲线纤维增强的先进复合材料，已被表现出优异的整体机械性能。然而，由于缺乏研究，VSC的断裂行为是工程结构设计中不可或缺的因素，目前尚不清楚。为了填补这一空白，本文提出了一种多相场方法来执行中尺度 VSC 薄板的失效分析，通过该方法将 VSC 薄板建模为各向异性而非均质的脆性材料。所提出的模型通过单边裂纹和开孔 FRC 薄板的断裂行为实验结果进行了验证。然后对不同设计下预开裂和开孔 VSC 薄板的失效分析进行了系统研究。结果表明，裂纹的传播始终与带缺口的 VSC 薄层中的纤维取向一致。此外，在某些设计中可以惊人地观察到载荷-位移曲线所展示的渐进式失效模式。此外，还根据建模结果提供了设计具有不连续性的 VSC 的指导。我们在设计新型抗断裂 FRC 方面提出的基本见解可能会促进 VSC 在汽车和航空航天结构中的应用。结果表明，裂纹的传播始终与带缺口的 VSC 薄层中的纤维取向一致。此外，在某些设计中可以惊人地观察到载荷-位移曲线所展示的渐进式失效模式。此外，还根据建模结果提供了设计具有不连续性的 VSC 的指导。我们在设计新型抗断裂 FRC 方面提出的基本见解可能会促进 VSC 在汽车和航空航天结构中的应用。结果表明，裂纹的传播始终与带缺口的 VSC 薄层中的纤维取向一致。此外，在某些设计中可以惊人地观察到载荷-位移曲线所展示的渐进式失效模式。此外，还根据建模结果提供了设计具有不连续性的 VSC 的指导。我们在设计新型抗断裂 FRC 方面提出的基本见解可能会促进 VSC 在汽车和航空航天结构中的应用。