へき開破壊応力および破壊じん性の確率的性質

抄録

Based on the view that the criterion for the cleavage fracture strength of steels is given by the maximum tensile stress, experiments were performed on a mild steel to study the probabilistic nature of the cleavage fracture stress and fracture toughness. These tests were carried out on smooth round bar tensile specimens, notched round bar tensile specimens and 3-point bend fracture toughness specimens.
The cleavage fracture stress in the smooth and notched specimens obeyed the Weibull distribution, but the fracture stress in the notched specimens took higher values than the one in the smooth specimens and the Weibull parameters were different in both specimens. Such effect of notch or stress gradient on the cleavage fracture can be quantitatively explained by statistical FEM analysis based on the Weakest Link Theory. The predicted values of the cleavage fracture stress for the notched specimens which were obtained by the use of the statistical parameters experimentally determined from the tests of smooth specimens, have shown a good agreement with the experimental results. This statistical approach has also been applied to predict the probabilistic distribution of the cleavage fracture toughness. The present experimental results of 60 3-point bend specimens and other reference data on the probabilistic distribution of toughness show the trend to coincide with the theoretical prediction.