Mode II fracture toughness of interfaces in laminated structures is usually assessed through standardized tests. Standards are based on samples featuring regular shapes and uniform cross-sections, in which mode II propagation happens to be unstable. We explore here, via a semi-analytical approach, the potential of more complex geometry and shapes for stabilizing the crack propagation. Results demonstrate that an end-notch flexure (ENF) sample with increasing width along the propagation direction possesses a more stable fracture compared to the classical configuration. This leads to the conceptualization of a width-tapered ENF (WTENF) that can address the instability issue encountered by the classical ENF samples. The closed-form solution of WTENF is derived, including the compliance and energy release rate of the system, based on which, the stability status diagram of WTENF has been provided. A systematic validation is performed by numerical and physical experiments, confirming the validity and the accuracy of the associated data reduction model. The WTENF can be a robust method with enhanced stability for measuring the mode II delamination toughness. Beyond solving the WTENF, the derived equations hold significant potential for other applications, such as probing the length-scale effect for delamination of fiber-reinforced composites and guiding the design of toughening strategies for interfaces.

中文翻译：

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迈向稳定的端部缺口弯曲 (ENF) 测试


层合结构中界面的 II 型断裂韧性通常通过标准化测试进行评估。标准基于具有规则形状和均匀横截面的样本，其中 II 型传播恰好不稳定。我们在这里通过半解析方法探索更复杂的几何形状和形状稳定裂纹扩展的潜力。结果表明，与经典配置相比，沿传播方向宽度增加的端部缺口弯曲（ENF）样品具有更稳定的断裂。这导致了宽度锥形 ENF (WTENF) 的概念化，它可以解决经典 ENF 样本遇到的不稳定问题。推导了WTENF的闭式解，包括系统的顺应性和能量释放率，并在此基础上给出了WTENF的稳定性状态图。通过数值和物理实验进行系统验证，确认相关数据缩减模型的有效性和准确性。 WTENF 是一种稳健的方法，具有增强的稳定性，用于测量 II 型分层韧性。除了求解 WTENF 之外，导出的方程在其他应用中也具有巨大的潜力，例如探索纤维增强复合材料分层的长度尺度效应以及指导界面增韧策略的设计。