Abstract Towards measuring the mixed-mode I + III fracture toughness independent of geometry and loading type, two test specimens were numerically and experimentally compared. The capabilities of edge-notched disc bend (ENDB) and edge-notched diametrically compressed disc (ENDC) fracture test specimens were compared in producing the full range of mixed-mode I + III. Although the geometry of both specimens was similar, the difference of their loading type (i.e., bending and compression) noticeably affected the mixed-mode I + III fracture parameters. The existence of mixed-mode I + III fracture in the crack front of the ENDC specimen was more stable than the ENDB specimen. However, the variation of mode mixities ratio in the ENDC specimen was more sensitive to the rotation of the crack inclination angle than the ENDB specimen. The map of T-stress as the function of mixed-mode I + III geometry factors plotted for both specimens. There was an optimal crack length in the ENDB specimen by which the full range of mixed-mode I + III fracture toughness can be measured independent of geometry and loading type effects. While for the ENDC specimen, the optimum crack length only existed for pure mode III. The full range of mixed-mode I + III fracture toughness tests were performed using both test specimens. The corresponding fracture loads and fracture initiation angles were also obtained for both ENDB and ENDC specimens made of granite rock. The magnitude of pure mode I fracture toughness measured by the ENDB specimen was greater than the ENDC specimen. Conversely, the pure mode III fracture toughness measured by the ENDC specimen was greater than the ENDB specimen. These discrepancies were also predicted by the computed T-stress map. In addition to the T-stress, Tz, process zone size, and the stress triaxiality constraints, which governed the crack propagation path were other effective parameters on the difference between mixed-mode I + III fracture toughness values measured via both specimens.

中文翻译：

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两种混合模式I+III断裂试样的比较

摘要 为了测量独立于几何形状和加载类型的混合模式 I + III 断裂韧性，对两个试样进行了数值和实验比较。在生产全系列混合模式 I + III 时，比较了边缘缺口圆盘弯曲 (ENDB) 和边缘缺口直径压缩圆盘 (ENDC) 断裂试样的能力。尽管两个试样的几何形状相似，但它们加载类型（即弯曲和压缩）的差异显着影响了混合模式 I + III 断裂参数。ENDC 试样裂纹前沿存在 I+III 混合型断裂比 ENDB 试样更稳定。然而，ENDC 试样中模式混合比的变化对裂纹倾斜角的旋转比 ENDB 试样更敏感。T 应力图作为混合模式 I + III 几何因子的函数，为两个试样绘制。ENDB 试样中存在最佳裂纹长度，通过该长度可以独立于几何形状和载荷类型效应测量全范围的混合模式 I + III 断裂韧性。而对于ENDC试样，最佳裂纹长度仅存在于纯模式III。使用两种试样进行全范围混合模式 I + III 断裂韧性测试。对于由花岗岩制成的 ENDB 和 ENDC 试样，也获得了相应的断裂载荷和断裂起始角。ENDB 试样测得的纯 I 型断裂韧性的幅度大于 ENDC 试样。相反，ENDC 试样测得的纯 III 型断裂韧性大于 ENDB 试样。计算出的 T 应力图也预测了这些差异。除了 T 应力、Tz、工艺区尺寸和应力三轴性约束之外，控制裂纹扩展路径的其他有效参数是通过两个试样测量的混合模式 I + III 断裂韧性值之间的差异。