Local strain energy density applied to martensitic steel plates weakened by U-notches under mixed mode loading

The averaged value of the strain-energy density over a well-defined volume is used to assess the static strength of U-notched specimens under mixed mode loading (I + II). The volume is centered in relation to the maximum principal stress present on the notch edge, by rigidly rotating the crescent-shaped volume already used in the literature to analyze U- and V-shaped notches under mode I loading. In total 96 new tests have been carried out on specimens made of structural steel with a martensite phase weakened by U-notches. The notch root radius varies from 0.2 to 2.0 mm while the notch depth is equal to 5, 7.5, 10 and 15 mm, respectively. In addition, for the lowest value of the notch depth (5 mm), some data from cracked specimens are summarized in the paper. Good agreement was found between experimental results and theoretical assessment based on the averaged strain energy density criterion under mixed mode loading.