Fracture assessment of U- and V-notches is important in mechanical engineering. One can use the J-integral as fracture parameter in order to predict the critical fracture load in notches.
The critical value of the J-integral in cracks is a function of the material properties. In notches, however, the material properties as well as the notch dimensions affect this critical value (named fracture toughness). So, one should carry out a complex and timeconsuming experiment in order to find the fracture toughness. In this paper, a practical equation has been derived to evaluate the critical value of the J-integral in blunt V-notches under Mode I loading. By means this new expression, only the notch dimensions and the critical value of the J-integral in cracks should be known. In this paper, the effect of the notch angle, the control volume radius to the notch root radius ratio (Rc/r), and the Poisson’s ratio on the J-integral and the critical value of the Jintegral have been studied. Results have shown that by increasing the notch angle and the Poisson’s ratio, the fracture toughness decreases. However, the fracture toughness increases by increasing the Rc/r ratio.