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Temperature dependences and rate effects on Mode II fracture toughness determined by punch-through shear technique for granite
Theoretical and Applied Fracture Mechanics ( IF 5.3 ) Pub Date : 2021-06-12 , DOI: 10.1016/j.tafmec.2021.103029
Tubing Yin , Xiaosong Tan , You Wu , Zheng Yang , Mingjian Li

Most studies of thermal effects on rock fracture have focused on Mode I, while the temperature-dependence and loading rate effect on Mode II fracture are rarely involved. We present the static and dynamic punch-through shear (PTS) tests, implemented on the INSTRON 1342 and the modified split Hopkinson pressure bar (SHPB) system respectively, as the approaches for determining the Mode II fracture toughness (KIIC) of PTS specimens at a series of thermal treatments and loading rates. As any macroscopic characteristic of rock is related to its microscopic or mesoscopic structures and properties, the SEM technique is thus applied to observe the mesoscopic morphology of heated and tested specimens. The fracture mode in the static and dynamic PTS tests is verified to be the dominant Mode II by fracture surface SEM observations. The results show that static KIIC (KIICS) increases with the thermal treatment temperature while static Mode I fracture toughness (KIC) is almost unchanged within 200 °C, and they all decrease substantially from 200 °C to 600 °C. Moreover, the dynamic KIIC (KIICD) at each thermal treatment temperature appears obvious loading rate effect. The strengthening effect of high loading rate on KIICD is almost unchanged below 400 °C, while the thermal effect on KIICD/KIICS becomes apparent when the temperature reaches 600 °C. The SEM observation displays that almost no cracks initiating within 200 °C, and the growth of obvious intergranular and transgranular cracks commence at about 400 °C and 600 °C, respectively. Besides, reticular cracks start to generate at 400 °C. As such, the mesoscopic characteristics at different thermal treatment temperatures are in accord with the variations of physical and mechanical parameters.



中文翻译:

通过花岗岩的穿通剪切技术确定的温度依赖性和速率对模式 II 断裂韧性的影响

大多数岩石断裂热效应的研究都集中在模式 I 上,而很少涉及温度依赖性和加载速率对模式 II 断裂的影响。我们介绍了分别在 INSTRON 1342 和改进的分体式霍普金森压力棒 (SHPB) 系统上实施的静态和动态穿通剪切 (PTS) 测试,作为确定模式 II 断裂韧性 ( K II C) 的方法) 在一系列热处理和加载速率下的 PTS 试样。由于岩石的任何宏观特征都与其微观或细观结构和性质有关,因此应用扫描电镜技术来观察加热和测试样品的细观形态。通过断口扫描电镜观察证实静态和动态 PTS 测试中的断裂模式是主要的模式 II。结果表明,静态K II C (一世一世C) 随热处理温度升高而增加,而静态 I 型断裂韧性 ( K I C ) 在 200 °C 内几乎没有变化,并且它们从 200 °C 到 600 °C 都大幅下降。此外,动态K II C (一世一世CD)在各热处理温度下出现明显的加载速率效应。高加载率的强化效果一世一世CD 在 400 °C 以下几乎没有变化,而热效应对 一世一世CD/一世一世C当温度达到 600°C 时变得明显。SEM观察表明,在200°C内几乎没有裂纹萌生,明显的晶间和穿晶裂纹分别在400°C和600°C左右开始生长。此外,在 400 °C 时开始产生网状裂纹。因此,不同热处理温度下的细观特性与物理和机械参数的变化一致。

更新日期:2021-06-17
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