Mechanical fatigue is a well-known and well-understood ageing mechanism. Research directly related to mechanical fatigue is nearly absent in Euratom FP4 and FP5 because the basic research on main contributing factors and typical materials used in operating nuclear power plants (NPPs) has already been performed in previous programmes or in non-nuclear research projects. Concerning mechanical fatigue projects dealing with lifetime assessment and management (GRETE and VERLIFE) and nuclear fusion (NET) have been launched in this period. In projects from Euratom FP6 (RAPHAEL) and FP7 (ARCHER, GETMAT, HELIMNET and MATTER) research projects related to mechanical fatigue can be found but the focus has been on characterising the behaviour of materials intended for Gen IV reactor systems.
Further non-nuclear research performed in the same period as the Euratom FP4 through FP7 and related to mechanical fatigue has been taken into consideration in this synthesis to gain benefit for the nuclear field. The relevant projects concerned lifetime assessment methods (FITNET), standardisation issues (TMF-STANDARD), non-destructive examination and monitoring techniques (GRETE), and fatigue design of components (7210-MA/131, 7210-MA/823, 7210-MA/951 and 7210-PR/303), either funded by other EC programmes, by the European Coal and Steel Community (now RFCS) or addressed by JRC Direct Actions.
The results from research projects concerning lifetime assessment and management can be directly applied because they are addressing a specific NPP type like in the VERLIFE project or provide generic guidance not restricted to a single industry as in the FITNET project. Also improved non-destructive monitoring techniques which have been investigated in JRC Direct Actions and in the GRETE project as well as standardisation efforts for thermo-mechanical fatigue made in the TMF-STANDARD project can be directly applied in the nuclear research field or NPPs. Application in NPPs may require conformance with regulations and therefore additional work.
Models to describe multiaxial load (7210-MC/109 and JRC Direct Actions) or creep-fatigue (MATTER) may have to be evaluated for materials and operating conditions of NPPs and need adjustments before being used in the nuclear field but provide the foundation for more sophisticated and realistic or easier to use models to predict fatigue or creep‑fatigue life.
Within some projects, including 7210-MA/131, 7210-MA/823, 7210-MA/951, GRETE, NET and MATTER, specific parameters (fluence, fluence rate, hold-time and cold-work) affecting fatigue have been investigated mainly for austenitic stainless steels. The projects are partially focused on synergisms of mechanical fatigue with other degrading effects, i.e. irradiation and thermal creep. Besides the gained knowledge in these synergisms, the data can improve the basis of already existing fatigue data for mechanical fatigue if test conditions are comparable to the ones in operating European NPPs. Also experiments performed at elevated temperatures (> 500 °C) are relevant for advanced gas-cooled reactors (AGRs) to improve knowledge of creep-fatigue.