TABLE OF CONTENTS As seen in section 6.2, the fatigue phenomenon of materials consists of a progressive damaging, resulting from cyclic loading and leading to fracture. "Low-cycle fatigue" corresponds to a lifetime N r resulting from the application of a cyclic loading less than 10 5 cycles. For a majority of metallic materials, such a lifetime corresponds to a strain level higher than the yield strength of the tested material. Thus, at each cycle, the cyclically loaded material is subjected to a plastic deformation in the bulk and it is the accumulation of plastic deformation, successively in traction and compression, which leads to progressive damage. This is why the term "plastic fatigue" is often used.
Low-cycle plastic fatigue damage is essentially found in structures designed with low yield strength materials (austenitic stainless steel for example, at ambient temperature as well as at high temperature) and in structures loaded at high temperatures (aeronautical structures made of light alloys or super alloys for example). In these structures, loading in low-cycle plastic fatigue particularly concerns stress concentration zones at notches, where there is a cyclic plastic zone at the notch root; however, very often this zone remains confined in an elastic surrounding medium. A study of the behavior and fatigue strength of such structures can be approached in two ways: tests, most of the time uni-axial and tensile/compression, are carried out either on stress controlled loaded notched test pieces or on strain controlled loaded test pieces of constant...
