Hydraulic fracture is important in unconventional oil and gas exploration. During the propagation of the hydraulic fracture, the crack tip is blunted due to the development of the process zone in the near-tip area. In this study, the blunting of the hydraulic fracture in polymethyl methacrylate specimens due to multi-timescale stress concentration is investigated. The ratio of the initiation toughness to the arrest toughness of the blunted hydraulic fracture is measured using both the dynamic and the static methods. Results show that a hydraulic fracture can be blunted with the time span of stress concentration from 1 ms to 600 s. It is also shown that the blunting of hydraulic fracture is a highly localized process. The morphology of the blunted crack depends on the stress distribution in the vicinity of the crack tip.

水力压裂在非常规油气勘探中很重要。在水力压裂的传播过程中，裂纹尖端由于近尖端区域中加工区域的发展而变得钝了。在这项研究中，研究了由于多时间尺度应力集中而导致的聚甲基丙烯酸甲酯试样中水力破裂的钝化。使用动态和静态方法来测量钝化水力裂缝的初始韧性与阻止韧性的比率。结果表明，在应力集中从1 ms到600 s的时间范围内，水力压裂可以钝化。还表明，水力压裂的钝化是高度局部化的过程。钝化裂纹的形态取决于裂纹尖端附近的应力分布。