Thermal ratcheting under biaxial stress states

Thermal ratcheting, the phenomenon of net strain accumulation due to plastic straining of pressure vessels under cyclic thermal loading, is an important factor in the design of nuclear reactor pressure vessels. In this paper a cyclic thermal gradient loading idealized by means of a step distribution through the pressure vessel wall and biaxial thermoelastic-plastic stress-strain models presently used in design calculations are adequate for spherical and cylindrical shells under internal pressure; however, for uniaxial loading and for torsional loading, the use of these models may underestimate the accumulated ratchet strain. (Auth.)