Re-Autofrettage

Loading, unloading, and reloading behavior of high-strength steel AISI 4340 (with yield strength of $1080MPa$⁠) has been measured using the round bar specimen and method described in (Jahad, H., and Ghanbari, G., 2003, ASME J. Pressure Vessel Technol., 125, pp. 321–325). Tests were conducted at plastic strains up to 3.4% for unloading and reloading. Re-autofrettage is the process of reapplication of overload pressure on an already autofrettaged tube. The question of whether reautofrettage results in a more beneficial compressive stress distribution and, therefore, in extension of life is examined in this study. Because of the profound influence of the Bauschinger effect on the unloading and reloading behavior of high-strength steel, the actual behavior of 4340 steel is used in calculations. It has been shown that with different combinations of first and second overload pressure, higher compressive stress is obtained as compared to a single autofrettage. Using a range of first and second autofrettage pressure, the compressive stress resulted by re-autofrettage is given.