In this research, with the aim to estimate the onset of fracture in key-hole notched components, made of brittle materials and subjected to combined tension-tear loading, the fracture limit curves are developed in terms of the notch stress intensity factors (NSIFs) based on the maximum tangential stress (MTS) and mean stress (MS) criteria. In order to verify the curves developed, a series of fracture tests are carried out on key-hole notched specimens made of PMMA using an improved loading configuration. The samples are prepared with three various notch tip radii for the sake of evaluating the influence of the notch tip radius on the fracture toughness of the key-hole notched samples. It is shown that for all notch tip radii, the fracture limit curves for both MTS and MS criteria are in very good consistency with the experimental data. No meaningful difference is found between the curves of MTS and MS criteria, especially under plane-stress conditions. It is also observed that the notch fracture toughness of the PMMA specimens could be well estimated under both plane-stress and plan-strain conditions.

在这项研究中，为了估计由脆性材料制成并承受拉伸-撕裂载荷的关键孔缺口部件的断裂开始，根据缺口应力强度因子（NSIF）绘制了断裂极限曲线。基于最大切向应力（MTS）和平均应力（MS）标准。为了验证所形成的曲线，使用改进的载荷配置对由PMMA制成的键孔缺口试样进行了一系列断裂试验。为了评估切口尖端半径对键孔切口样品的断裂韧性的影响，用三种不同的切口尖端半径制备样品。结果表明，对于所有缺口尖端半径，MTS和MS标准的断裂极限曲线与实验数据非常吻合。在MTS和MS标准的曲线之间没有发现有意义的差异，尤其是在平面应力条件下。还观察到，在平面应力和平面应变条件下，都可以很好地估计PMMA试样的缺口断裂韧性。