A MODIFIED MICROSTRUCTURE-BASED CREEP DAMAGE MODEL FOR CONSIDERING PRIOR LOW CYCLE FATIGUE DAMAGE EFFECTS

摘要

A modified continuum damage mechanics (CDM) model was proposed to predict the creep behavior of P92 steel with prior low cycle fatigue (LCF) damage. In order to investigate the damage mechanisms of prior LCF, microstructural observations of P92 steel after various prior LCF and subsequent creep exposures were performed. Results show that the key creep degradation is associated with the martensite lath recovery. Based on the physics of microstructural evolutions, three state variable formulas which represent damage mechanisms related to martensite lath recovery were employed to account for the prior LCF damage. The three state variable formulas which describe the damage evolution with prior LCF cycles were coupled with Hayhurst CDM model. The main advantage of the modified CDM creep model lies in its ability to directly predict creep behavior with different levels of prior LCF damage. The only parameter needed to be known for the prediction is the martensite lath width after prior LCF. Comparison of the predicted and experimental results shows that the proposed model can give a reasonable prediction for creep behavior. Moreover, this model also shows good predictive ability at different strain amplitudes of prior LCF.