A LIFETIME PREDICTION MODEL FOR SINGLE CRYSTAL SUPERALLOYS SUBJECTED TO THERMOMECHANICAL CREEP-FATIGUE-OXIDATION DAMAGE

摘要

This paper contains a brief description of a lifetime prediction model for Single Crystal Superalloys operated at high temperatures and subjected to creep, fatigue and oxidation damage mechanisms. The model aims at predicting engineering life to crack initiation and describing dominating damage mechanisms and their non-linear interaction in such materials. Microcracks propagation from initial casting pores is considered as the critical life-limiting factor. The initial damage, before any type of loading, is therefore quantified with the help of pores' statistical distribution. Microcracks propagation is described through creep-fatigue interaction under globally elastic or plastic material behaviors. Interaction of surface oxidation with creep-fatigue damage is described as drop of material strength within and beyond the oxidized zone. Different model parameters are obtained directly from materials tensile, creep and LCF test data at different temperatures. Some parameters, independent of temperature, are fitted on a large variety of LCF test data. Another set of LCF and TMF test data has been used to compare model predictions with. As a validation test of model prediction capabilities, lifetime of numerous LCF and TMF tests with various cycle shapes and on different material orientations has been calculated to a significant level of accuracy. Another validation test reported in here is the surface crack growth measured on the specimens and predicted accurately through this model.