Metal plasticity and fatigue at high temperature

The situation in which a component or structure is maintained at high temperature under the action of cyclic thermal and/or mechanical loadings represents, perhaps, one of the most demanding engineering applications—if not, in fact, the most demanding one. Examples can be found in many industrial fields, such as automotive (cylinder head, engine, disk brakes), steel-making (hot rolling), machining (milling, turning), aerospace (turbine blades), and fire protection systems (fire doors). The presence of high temperatures usually induces some amount of material plasticity or creep deformation in the most stressed regions of the structure. Plasticity, if combined with the action of cyclic loading variation, may lead to low-cycle fatigue (LCF) failure. In order to estimate the component fatigue life in such demanding operative condition, it is often necessary to characterize the high-temperature material behavior under cyclic loading, in terms, for example, of cyclic stress–strain response, strain hardening or softening, creep behavior, experimental fatigue strength under isothermal and/or non-isothermal conditions. Moreover, it is also necessary to develop a reliable structural durability approach that is able to include experimental results in numerical and/or predictive models (e.g., plasticity models, fatigue strength curves). The choice of the most appropriate material model to be used in simulations, or even calibrating the model to experimental data, often represents the most critical step in the whole design approach. Experimental techniques and modeling have to be properly managed to guarantee the reliability of the estimated fatigue life.