3-DIMENSIONAL FINITE ELEMENT T-STRESS CALCULATION FOR REACTOR PRESSURE VESSEL NOZZLE BLEND RADIUS SEMI-ELLIPTICAL SURFACE CRACKS

T-stress is used as an indicator of the condition of crack tip constraint. In current fracture mechanics engineering applications in the U.S. nuclear industry, T-stress generally has been ignored during the calculation of applied stress intensity factors (SIF). Consideration of this crack tip constraint component could affect the evaluation of material fracture behavior, under either plane strain or plane stress or plane strain and plane stress combination. When the T-stress shows that the condition of crack front constraint is not plane strain, incorporation of T-stress may allow reduction of unnecessary conservatisms in such calculations. Under this condition, the allowable stress intensity factor is modified by increasing it above the KID value, and it potentially increases the predicted allowable flaw sizes. In this paper, T-stress has been calculated using 3-D finite element analyses (FEA) with a typical semi-elliptical crack in a reactor pressure vessel (RPV) nozzle blend radius. Both thermal and internal pressure load cases are considered. To verify this finite element analysis approach, this method is applied to comparable literature models. The FEA results are consistent with closed-form solutions for T-stress calculation.