In the present research, two brittle fracture criteria were developed in terms of the notch stress intensity factors to predict mode I fracture in engineering components weakened by V-notches with end holes (VO-notches). The criteria were based on the point stress and the mean stress failure concepts. To evaluate the validity of the criteria, first, 36 new fracture tests were conducted on a new notched specimen, namely the Brazilian disk containing central V-notch with end hole (VO-BD specimen) made of polymethyl-metacrylate. Three notch angles and four notch radii were considered in the experiments. Then, the experimentally obtained fracture loads were converted to the corresponding mode I notch fracture toughness values by mean of the finite element method in order to compare the test results with the theories. It was found that very good agreement exists generally between the experimental and theoretical results. Also, found in this research was that by increasing the VO-notch angle, the accuracy of the mean stress criterion decreases, particularly for larger notch radii. Although the accuracy of the criteria depends significantly on the notch geometry, except for the angle 90°, the average discrepancies of the mean stress criterion were less than 8.5% as well as those of the point stress criterion for the entire angles showing acceptable accuracy of the predictions.

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In the present research, two stress-based failure criteria were proposed to predict brittle fracture in components containing V-notches with end holes (VO-notches) under mixed mode I/II loading. The first criterion, called VO-MTS, was an extension of the maximum tangential stress (MTS) criterion, and the second one, called VO-MS, was developed based on the mean stress (MS) failure concept. Two different groups of critical distances were utilized in the predictions. The first group was equal to the critical distances for sharp crack, and the second one was computed by using the mode I fracture test results on notched specimens. To verify the criteria, the theoretical fracture curves were compared with numerous experimental results gathered from 108 new brittle fracture tests performed on the Brazilian disk specimens weakened by central V-notches with end holes and made of PMMA under mode I and mixed mode I/II loadings. It was found that both the criteria provide very good predictions to the experimental results for different mode mixity ratios. Also, found in this research was that the curves are almost independent of the critical distance groups, meaning that one can simply utilize the critical distances of sharp crack in both the VO-MTS and the VO-MS criteria without requiring performing mode I VO-notch fracture experiments. List of symbolsCTSN Compact-tension-shear-notch CZM Cohesive zone model d Total slit length in the VO-BD specimen D Diameter of the VO-BD specimen d c Critical distance of the MS criterion for sharp cracks d c,vo Critical distance of the MS criterion for VO-notch E Young's modulus ERNFT Effective relative notch fracture toughness FE Finite element FFM Finite fracture mechanics FNR Fictitious notch radius K vo eff Effective relative notch fracture toughness K IC Plane-strain fracture toughness of material K vo I Mode I notch stress intensity factor