Deformation conditions in the vicinity of concentrators at low-cycle stress of sizeable samples from reactor pressure vessel material

Deformation conditions were investigated in a reactor pressure vessel in the vicinity of points where stress and deformation concentrate to a multi-axis stress. The cycle deformation growth in the notch root in the first cycle of low-cycle fatigue stress of a sizeable flat bar with a bore, made from the 15Kh2MFA material, with a transient force cycle may be expressed using the Neuber formula αsub(H)sup(2)=αsub(delta).αsub(epsilon) considering the deformation curve delta - epsilon. In the second and other cycles the procedure does not yield reliable predictions because it does not consider the strengthening of the plasticized area in the notch root and the formation of inner pressure stress after the first cycle. For a transient cycle of stress of a flat bar with a bore (αsub(H) is approximately 2.6) the pressure stress in the notch root can be considered to attain a level of (0.5 to 0.6).deltasub(0.2) in the second cycle and of (0.2 to 0.35).deltasub(0.2) in a half of service life. Taking into consideration the expression (deltasub(N) - deltasub(NZ)) instead of deltasub(N) in the Neuber hyperbola equation can offer more accurate prediction of cyclic deformation in the notch root and in the second and other cycles than the conventional Neuber method. The results of the study of deformation conditions in the vicinity of the bore in the flat bar can be also applied to the areas of stress concentrators in the pressure vessel and can be used for the rendition of the vessel reliability results more accurate. (B.S.)