Cleavage fracture and irradiation embrittlement of fusion reactor alloys: mechanisms, multiscale models, toughness measurements and implications to structural integrity assessment

In-Service Design & Performance Prediction of Advanced Fusion Material Systems by Computational Modeling and Simulation

“…Fits to the universal shape of the MC, its lower shelf minimum and T o shifts (!T o ) due to irradiation hardening require a K µ (T) that is mildly temperature dependent above about 0 °C [17][18]. The K Jc (T), based on fitting the corresponding "*(T), model is in good agreement with both the universal shape of the MC as well as irradiation induced !T o .…”

“…T o shifts (!T o ) are used to account for various effects of size and geometry, loading rate and irradiation embrittlement (!T). The multiscale model, relating atomic to structural scale fracture processes, underpins the MC-!T method [17][18].…”

“…At the atomic scale, we proposed that the intrinsic micro-arrest toughness, K µ (T), of the bcc ferrite solute strengthened lattice dictates an invariant shape of the macroscopic K Jc (T) curve [17][18]. We developed a model that shows that K Jc (T) is controlled by the alloy's true stress-strain ("#$) constitutive law, "(T,$), combined with a temperaturedependent critical local stress, "*(T) and critical stressed volume, V*.…”

From materials development to their test in IFMIF: an overview

“…Therefore, adequate methods to account for the specimen size and geometry effects on the fracture toughness have to be developed. Neutron irradiations are always detrimental for the fracture properties of RAFM and ODS RAFM steels, whose crystalline structure is bcc [38]. It is well known that the metals and alloys with a bcc structure exhibit a ductile-to-brittle transition of the fracture mode by decreasing the temperature.…”

“…The amplitude of the temperature shift depends on the irradiation conditions: temperature, neutron flux and fluence, amounts of helium and hydrogen produced by nuclear transmutation reactions, and so on. The method of the master curve, based on the determination of the reference temperature T o that indexes a median universal toughness-temperature curve at 100 MPa m 1/2 , appears as a powerful method to determine the temperature shift with a limited number of specimens [38].…”