INVESTIGATIONS ON FATIGUE CRACK PROPAGATION UNDER CYCLIC ISOTHERMAL AND THERMO-MECHANICAL LOADINGS FOR A TYPE 304L STAINLESS STEEL

摘要

This paper deals with crack propagation under cyclic thermo-mechanical loads, as encountered in PWR piping. To compute the crack propagation rate, the French RSE-M Code requires applying a plastic correction (Irwin's correction and a coefficient) to the stress intensity factor, since austenitic steels are very ductile. Additional investigations have been conducted at CEA to improve this correction. In a first step, an isothermal test campaign was performed on CT-specimens with various loading conditions (0.10 < R < 0.80), showing that the application of a plastic correction on K is not necessary. In a second step, a new device called "PROFATH" was built. The specimen is a thick-walled 304L stainless steel tube, and cyclic loads are applied: in a first part of the cycle, the external wall is heated by a high frequency induction coil, and in a second part of the cycle, heating is stopped and the internal wall is cooled by running water. To be sure that only one crack will grow, a sharp circumferential groove is machined at the outer surface in the heated portion of the tube. A constant tensile loading is applied to the specimen. The paper describes the test set up and the instrumentation used to follow the crack propagation along the test, presents the main experimental results and finally gives their interpretation.