Prediction of crack resistance for heat-resistant steels taking into account the specimen size effect. Communication 1. Results of experimental investigations

We present a large volume of unique experimental data on local fracture parameters and crack resistance characteristics of different structural alloys, including steels 15Kh2MFA and 15Kh2NMFA and their welded joints, subjected to different heat treatments, simulating exposure to different doses of radiation bombardment and used in manufacturing VVéR-440 and VVéR-1000 atomic reactor pressure vessels. These experimental results allow us to generalize the scientific conclusions concerning the scale effect in fracture mechanics, since they were obtained by investigating many materials (σ_0.2 = 270–1500MPA) over a broad range of variation in specimen thickness (t=12.5–150 mm) and experimental temperature (T=77–573 K). The data on the fracture toughness characteristics of a broad class of structural alloys suggest that the scale effect is complex and contradictory, depending first of all on the range of variation in the specimen thickness and the physicomechanical properties of the material, including those determined by the effect of production and service factors. On the whole, the experimental data support the possibility noted in various literature sources that there are three different types of dependences of the fracture toughness on the specimen size (the fracture toughness can increase, decrease, or stay the same as the specimen size increases). It does not seem possible to predict and explain these dependences within approaches proposed earlier. Translated from Problemy Prochnosti, No. 1, pp. 5–25, January–February, 1997.