Investigation of ratcheting characteristics of modified 9Cr-1 Mo steel by using the Chaboche constitutive model

In this paper, an inelastic constitutive equation of the Chaboche model, which can simulate ratcheting behaviour at high temperatures, is investigated for modified 9Cr-1Mo steel. The plastic modulus, which primarily governs the calculation scheme for plasticity, is derived for the Chaboche model and implemented into a computer program with the radial return algorithm to compute the cyclic backstress components. With the cyclic test data of modified 9Cr-1Mo steel, the Chaboche three-decomposed constitutive parameters of the kinematic hardening rule and the isotropic softening rule, which controls the cyclic softening characteristic of modified 9Cr-1Mo steel, are identified by a simple method. By using the identified constitutive parameters, the ratcheting behaviour of modified 9Cr-1Mo steel is simulated to investigate the effects of mean stress levels at a certain stress amplitude and ratcheting parameter's values. In particular, the progressive deformation instability phenomena due to the cyclic softening characteristics of modified 9Cr-1Mo steel are investigated. (C) 2007 Elsevier Ltd. All rights reserved.