Prediction of fracture toughness for heat-resistant steels considering specimen dimensions. Report 4. Fracture toughness after plastic prestraining of materials with cracks

The paper presents the results of an experimental investigation of the influence of warm prestressing (WPS) on fracture toughness characteristics of large-size specimens. The WPS has been found to be an efficient method for enhancing brittle fracture resistance of large-size bodies from the investigated materials and can be recommended for practical realization in nuclear reactors and other critical structures whose brittle fracture is impermissible both in the process of normal operation and in emergency situations. The optimum temperature-loading regime of the WPS is defined by both the properties of a given material and its thickness which governs the intensity of plastic deformation in the process of WPS. Based on the established mechanisms of the WPS effect, a physicomechanical model has been developed for the prediction of fracture toughness for pressure-vessel heat-resistant steels after WPS taking into account the influence of the stress state at the crack tip. The model makes it possible to predict fracture toughness for large-size bodies subjected to WPS with the given temperature and loading regimes from the results of testing small laboratory specimens. The most optimum regimes of the WPS can also be determined using this model and even those for several materials making up a structural component and subjected to the WPS. Translated from Problemy Prochnosti, No. 3, pp. 39–54, May–June, 1997.