The safety assessment of nuclear components requires that fracture mechanics material data or curves are available. These data must be measured with suitable specimens of the original material for the given condition, i.e., temperature and irradiation. Especially for reactor pressure vessel (RPV) weld material, fracture mechanics specimens are not available within the irradiation surveillance programs in sufficient number, or, if available, the performance of accurate fracture mechanics tests in hot cell facilities is extremely difficult.
New developments in the field of micromechanical material models taking into account the ductile damage process characterized by nucleation, growth, and coalescence of voids make it possible to determine micromechanical material parameters from tension tests and finite element analyses of notched and smooth specimens. If, in addition, a characteristic length, lc,is considered, the ductile fracture resistance behavior of fracture mechanics specimens and, hence, J-resistance curves may be predicted.
Here, the modified Gurson model is applied to calculate a static J-resistance curve for irradiated weld material from the results of smooth static tension tests out of the irradiation surveillance program of a specific nuclear power plant. Since original material was not available in sufficient quantity for fracture mechanics tests, a verification program was conducted comprising tests and analyses of smooth tension specimens and side-grooved compact (CT) and wedge opening loading (WOL) X-type specimens of two unirradiated and one irradiated weld materials. In every case, the predicted resistance curves are in good agreement with the measured curves.
Following the successful evaluation of static material tests, the first experimental and numerical steps are presented towards the evaluation of dynamic J-R curves from the results of instrumented Charpy tests.