Experimental verification of two stress-based criteria for mixed mode I/III brittle fracture assessment of U-notched components

In the present study, a series of fracture experiments are conducted on PMMA U-notched samples using an improved loading configuration, which is redesign of the apparatus recently presented for doing fracture tests under combination of tensile and out-of-plane shear loading. In order to assess the effect of notch tip radius, the tested specimens are fabricated with three different radii. Two brittle fracture criteria, namely the point stress (PS) and mean stress (MS), are employed to estimate the fracture resistance and the out-of-plane angle of fracture onset of the experiments. These criteria have previously been extended to general loading type of mixed mode I/II/III for studying fracture in engineering components containing blunt V-notches. Consequence of comparing the theoretical and experimental results for different notch tip radii reveals that both criteria are accurate enough to predict the fracture behavior of the U-notched engineering members subjected to mixed mode I/III loading. It is not found any considerable difference between the curves of fracture initiation angle and fracture resistance resulted from the PS and MS criteria. The criteria also show that the out-of-plane fracture angle due to pure mode III loading is constant and independent of the notch tip radius.