Ratchetting in the creep range

This report attempts to present a ''State of the Art'' of this problem from three contracting and complementary points of view which reflect separate traditions within the discipline of structural analysis. Part I gives a brief summary of the essential elements of the three constitutive parts and a set of conclusions and recommendations are then formulated. Part II is an attempt by a group at CEA Saclay, France, to distil from available experimental data a set of rules expressed in terms of the stress classifications of the ASME codes, which will ensure the prevention of excessive creep ratchetting. The resulting stresses to an effective (or reference) stress and the creep assessment is then made in terms of the creep produced by the effective stress. They aim at analytical procedures for LMFBR components that operate in the creep region and are subject to considerable thermal transients. Part III by Ponter and Cocks of the University of Leicester is a theoretical study of the problem using bounding and other approximate techniques. The problem is studied in a sequence of increasingly complex problems commencing with an isothermal structure subjected to constant load and terminating in a structure subjected to arbitrary cyclic thermal loading. The results are expressed in terms of a reference stress derived from a plastic shakedown solution, and a reference history of temperature. These techniques are capable of providing assessment of the creep deformation of a structure when the plastic shakedown properties of the structures are known. The particular circumstances which occur in a LMFBR are emphasized. Part IV by Corradi and Franchi discusses the methods by which finite element solution may be calculated. These are surveyed with particular reference to the numerical problems involved and the relationship between computational procedure and the form of the constitutive equation. 162 refs