The Application of Physically Based CDM Modeling in Prediction of Materials Properties and Component Lifetime

Since the early empirically based work of Kachanov and Robotnov substantial progress has been made in developing the concept of Continuum Damage Mechanics (CDM) as a tool for predicting material and component behavior in the creep regime. The key element in this process has been the progress that has been made in understanding and quantifying the physics of deformation and fracture in engineering alloys for high temperature service. In this paper, the application of the CDM methodology has been demonstrated in the prediction of the creep behavior of alloy steels for boiler pressure parts and for predicting the life to failure of model components and tubular testpieces operating in creep conditions. A model incorporating two damage state variables formed the basis of the methodology for creep behavior and a multi-axial variant of the model was used for the component life prediction. The important development described in this work has been the use of a simplifying procedure in dealing with damaged elements in the finite-element model, so that the analysis for component life prediction can be carried out on a personal computer rather than the large mainframe computers used previously. This greatly increases the usefulness of the procedure for practical design applications. The results show that the CDM methodology can be applied successfully in these important applications and will give much more satisfactory agreement with experiment than existing less robust methods. In addition the failure profile of the tubular testpieces can be accurately represented and this is a feature unique to the CDM approach.