Simplified method to predict creep-fatigue crack growth in inelastic situation. Evaluation of thermal fatigue crack growth test

Predicting crack growth is frequently required in the safety and residual life assessment of nuclear components. To evaluate the crack growth rate, the stress intensity factor range based on linear elastic fracture mechanics is most widely employed for assessing the light water reactor components. In fast reactor, however, the J-integral type non-linear fracture mechanics parameters should be used to incorporate effects of plasticity and creep in the prediction. To estimate J-integrals under general conditions, detailed finite element analysis of cracked component is required, consequently inelastic fracture mechanics is still difficult to use in practice due to its computational cost. Simplified methods approximating J-integrals are, therefore, needed, e.g. to perform sensitivity analysis covering uncertainties contained in the flaw assessment. The authors have been involved in a collaborative study between Nuclear Electric, plc. in the UK and CRIEPI in Japan, in order to develope and validate simplified method for evaluating crack growth in creep-fatigue loadings. Within this, one of the authors proposed three simplified estimation methods of elastic-plastic J-integral due to thermal stresses, and validated them numerically. The methods are based on stress intensity factors for given stress and strain distributions of uncracked geometry, thus the computational effort required is sufficiently small to allow practical crack assessment. This paper presents an experimental validation of the proposed methods by comparing the predictions with thermal fatigue crack growth tests. The tests were performed using type 304 stainless steel cylindrical specimens with semi-elliptical pre-notches under temperature cycles between 150 and 550degC. (author)