RATCHET BOUNDARY EVALUATION AND COMPARISON WITH RATCHETING EXPERIMENTS INVOLVING STRAIN HARDENING MATERIAL MODELS

摘要

Pressure components in nuclear power plants are designed to prevent the failure mechanism of incremental deformation or "ratcheting" due to the simultaneous application of mechanical loads such as pressure and cyclic loads. Design criteria using elastic methods that are specified in NB-3200 of ASME Section III Code are derived from a perfectly-plastic material model. The Code allows the use of plastic methods to demonstrate an acceptable response to cyclic loading, but does not provide clear guidance on any specific plasticity model to use. It has been shown in previous studies that some strain hardening plasticity models are unsuitable for establishing the absence of ratcheting. In this paper, the ratchet boundary obtained from the perfectly plastic and the strain hardening Armstrong-Frederick material models are examined based on the published experimental investigations of the classical Bree problem, pipe bends under in-plane bending and tension-torsion tests. Suitable criteria for evaluating the cyclic analysis response are discussed.