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THERFAT Résumé de rapport

Project ID: FIKS-CT-2001-00158
Financé au titre de: FP5-EAECTP C
Pays: France

Verification tests

By means of verification tests, damage tests on small-scale specimen (investigation of fatigue behaviour and fracture mechanics parameter) and on large-scale components using realistic mock-up configurations have been carried out. The selection of the large-scale test configuration was based on a comprehensive compilation of existing thermal fatigue laboratory test data and of information about the most fatigue relevant parameter (e.g. surface finishes, mean stress effects). In most fatigue tests performed so far mechanical loads were applied, only a few thermal load tests are known. Therefore, the THERFAT large-scale damage tests were focused on (severe) thermal shock loads. Tests on small specimen with mechanical loads were performed to compare the effects of mechanical to thermal loads. The experimental damage test pattern established in THERFAT was supposed to investigate realistic component or specimen resistance capabilities concerning specific degradation mechanisms (e.g. thermal shocks) to provide a better understanding of failure modes and the quantification of safety margins in terms of the load/stress-fatigue-crack initiation interaction and to single out the most relevant parameter that can serve as criteria for the verification and calibration of integrity procedures.

The achieved results in the experimental damage tests concerning the load bearing capability of components and regarding selected aspects of fatigue assessments confirm the predicted tendencies of higher load bearing capabilities than expected by application of common code analysis procedures. In terms of fatigue usage, all the experimental test results showed strain rates above or in accordance with the ASME-design fatigue curve, proving the currently applied fatigue curves (ASME design curve) as appropriate. The tests confirmed known tendencies, that the number of load cycles up to crack initiation is comparable between mechanical and thermal loads. But in the further development from crack initiation to failure, the current experience shows, that cracks caused by mechanical loads tend to propagate, while initiated cracks due to thermal loads appear to come to a crack arrest.

The results of the damage tests with the related analytic investigation are generally valid for all respective components subjected to cyclic thermal loads and are not only limited to Tee-connections.

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