This paper investigates the effect of loading rate on the mixed-mode I/II fracture behavior of PolymethylMethacrylate (PMMA). Experimental studies are performed using a novel fracture test specimen which has recently been developed, called short bend beam (SBB), in different loading rates of 1 mm/min, 20 mm/min, and 200 mm/min. Fracture test data are presented for pure mode I, pure mode II, and mixed-mode I/II conditions, thanks to the geometrical configuration offered by the specimen covering a full spectrum of mode mixities. Two fracture criteria including maximum tangential stress (MTS), and generalized maximum tangential stress (GMTS) are employed to predict the onset of fracture and the fracture initiation angle in different loading rates. The MTS criterion only considers the singular crack tip terms associated with the stress intensity factors (SIFs) in the solution while the GMTS includes the T-stress effect as well as the SIF-related terms. While enhanced predictions provided by the GMTS criterion, as compared to MTS results, reveals the significance of including the T-stress term in the theoretical calculations, the critical distance (r_c) is also found as another major parameter playing an important role in the fracture behavior. It is shown that the size of r_c decreases by increasing the loading rate. Therefore, for the first time, a variable and loading rate dependent r_c value is utilized for employment of the GMTS criterion and it is demonstrated that considering variable critical distance can provide acceptable theoretical predictions for different loading rates.

本文研究了加载速率对聚甲基丙烯酸甲酯 (PMMA) 混合模式 I/II 断裂行为的影响。使用最近开发的一种新型断裂试样进行实验研究，称为短弯曲梁 (SBB)，加载速率为 1 毫米/分钟、20 毫米/分钟和 200 毫米/分钟。由于样品提供的几何配置涵盖了全谱模式混合，因此提供了纯模式 I、纯模式 II 和混合模式 I/II 条件下的断裂测试数据。采用最大切向应力 (MTS) 和广义最大切向应力 (GMTS) 两个断裂准则来预测不同加载速率下的断裂开始和断裂起始角。T -应力效应以及 SIF 相关术语。虽然 GMTS 标准提供的增强预测与 MTS 结果相比，揭示了在理论计算中包含T应力项的重要性，但也发现临界距离 ( r _c ) 作为另一个主要参数在计算中发挥重要作用。断裂行为。它表明的大小ř _Ç通过增加加载速率减小。因此，对于第一次，可变和加载速率依赖ř _Ç值被用于就业GMTS标准的，它是表明考虑可变临界距离可以提供不同的加载速率上可接受的理论预测。