Abstract Concrete is the most commonly used material in civil engineering and also the most conventional and cheap material available in the market. Concrete cracking and fracturing may cause irreparable damages to concrete structures. Hence, fiber-reinforced concretes have been introduced in recent years as a strategy to eliminate these drawbacks to a large extent. In this study, crack propagation and the fracture toughness of concrete specimens without polypropylene (PP) fibers and those containing 0.2, 0.35, and 0.5 vol% of PP fibers were investigated through testing the straight notched Brazilian disc specimens. Furthermore, crack propagation from the pre-existing cracks in the specimens was investigated, and the mode I, mode II, and mixed-mode I/II fracture toughness were also calculated. The Brazilian disc (BD) test was performed on the specimens at different inclination angles of 0, 15, 28.83, 60, 75, and 90° relative to the direction of pre-existing cracks. According to the experimental results, at angles less than 75° (0

中文翻译：

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聚丙烯纤维对纤维增强混凝土中模式 I、模式 II 和混合模式断裂韧性和裂纹扩展的影响

摘要 混凝土是土木工程中最常用的材料，也是市场上最常规、最便宜的材料。混凝土开裂和压裂可能对混凝土结构造成不可修复的损坏。因此，近年来引入了纤维增强混凝土作为在很大程度上消除这些缺点的策略。在这项研究中，通过测试直缺口巴西圆盘试样，研究了不含聚丙烯 (PP) 纤维和含有 0.2、0.35 和 0.5 vol% PP 纤维的混凝土试样的裂纹扩展和断裂韧性。此外，研究了试样中已有裂纹的裂纹扩展，并计算了模式 I、模式 II 和混合模式 I/II 的断裂韧性。巴西圆盘 (BD) 试验是在相对于预先存在的裂纹方向的 0、15、28.83、60、75 和 90° 的不同倾角下对试样进行的。根据实验结果，角度小于 75° (0