Strain concentration factor of notched cylindrical bars under tension creep

Abstract

Variations in the new strain concentration factor (SNCF) with creep deformation have been studied for notched cylindrical bars. This new SNCF is based on the average axial strain, defined under the triaxial state of stress at the net section. The uniaxial creep constitutive equations employed in the finite element calculations are primary-tertiary, primary-secondary and tertiary creep. With creep deformation the new SNCF increases sharply from its elastic value and reaches a maximum. After that it gradually decreases from the maximum with creep deformation. The new SNCF decreases at any deformation level as the notch radius increases. However, it never becomes less than unity. The notch radius has the strongest effect on the SNCF from infinitesimal to large deformation. The difference in the type of creep constitutive equation has an effect on the SNCF only beyond the deformation level at the maximum SNCF. Creep deformation provides the pattern of the variation, i.e. an increase in the SNCF up to the maximum and subsequent gradual decrease. The conventional SNCF becomes less than unity after increasing from its elastic value to a maximum and then decreasing. The fact that the conventional SNCF is less than unity is contradictory to the concave distributions that the axial strain has on the net section at any deformation level. The new SNCF provides reasonable values, which are consistent with the concave distributions.