informationрусский
Proceedings of the conference

Margolin B.Z. Gulenko A.G. Fomenko V.N. Kostylev V.I.

New method to predict the temperature dependence of fracture toughness «Advanced unified curve»

The Unified Curve (UC) method is a method of predicting the temperature dependence of fracture toughness KJC(T) which is based on the Prometey model of brittle fracture. The UC method is analyzed from physical viewpoint and the reasonability of improving the method is shown. The Prometey model modification (the Prometey-M model) is presented. It is shown that the Prometey-M model allows explaining the complete consistency of experimental data obtained with using of different types of specimens (smooth and notched cylindrical tensile specimens and cracked specimens) at various temperatures. Based on the Prometey-M model the Advanced Unified Curve (AUC) method and a procedure determining the parameters of AUC are developed.

Transformation of KJC(T) curve under neutron irradiation was modeled by three variants.

In the first variant the material embrittlement was considered by the so-called non-hardening mechanism where the material embrittlement occurs not due to an increase in yield stress but only due to the formation of phosphorus segregations on various interphase boundaries as well as on the grain boundaries.

In the second variant the material embrittlement was considered by the so-called hardening mechanism where the material embrittlement occurs only due to an increase in yield stress.

In the third variant the material embrittlement was considered proceeding simultaneously by both hardening and non-hardening mechanisms. This embrittlement variant is the most typical of RPV steels under irradiation.

A comparison of AUC and UC is made as well as a comparison AUC and Master Curve (MC) method which is most widespread engineering method of predicting the temperature dependence of fracture toughness KJC(T). For these comparisons the extensive database on fracture toughness of materials with various embrittlement degrees was used.

It is shown that unlike the UC method, which gives adequate prediction of KJC(T) in the range of temperatures from -200°С to +200°С, the AUC method gives adequate predictions over a wide range of temperatures from -200°С to +350°С.

For low T0 values the AUC and MC methods describe experimental data nearly in the same way, i.e., there is no preference in using the above methods for this case. With increased T0 the AUC method describes the dependence KJC(T) more adequately than the MC method does. Therefore, the AUC method is recommended in predicting KJC(T) for any degree of material embrittlement.

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