5. Outlook and developments

Low-cycle fatigue tests were carried out on pure aluminum, a 304 L austenitic steel, a copper-cobalt-beryllium alloy and pure copper at different loading conditions, at imposed strain or stress, on different test machines. This campaign revealed the systematic presence of almost identical, recurring EA signals during these fatigue tests. Originating from a single source and triggered at virtually the same stress level every cycle, these acoustic multiplets are a specific signature of fatigue crack propagation. It would now be interesting to extend this type of analysis to other materials, such as certain polymers or metallic glasses for which incremental fatigue cracking has been observed, although the crack initiation mechanisms are very different, in order to test the extension of the non-destructive fatigue testing methodology proposed here to these classes of materials.