PSI - Issue 42

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Mark Kachanov et al. / Procedia Structural Integrity 42 (2022) 96–101 M.Kachanov, V.Mishakin, Y.Pronina / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 1. The evolution of microcrack density,  , and of the martensite content,  , in the process of loading, at various strain ranges. The end points (circled) correspond to fracture points (formation of macrocracks).

4. Conclusions The presented approach to monitoring the low-cycle fatigue of a metastable austenitic steel incorporates, in an essential way, the micromechanics considerations. The latter lead to the methodology of combining the acoustic monitoring tools with the eddy current technique. In particular, the following insights provided by micromechanics should be highlighted: • Generally, the effect of martensite particles on the overall elastic properties depends not only the particles’ volume fraction  , but, also, on particle shapes (and the shape dependence may generally be strong); the fact that the shapes may be complex and somewhat uncertain complicates the analysis. Micromechanics considerations show, however, that if the elastic contrast between the particles and the austenite phase is moderate (within 70-80%) then the shape effects can be neglected and the information on volume fraction  provided by the eddy current data is sufficient; • The possibility to replace the procedure (A), described in the preceding section, that is not non-destructive by the non-destructive procedure (B) follows from micromechanics considerations. Namely, the latter provide the following two insights: (I) smallness of the aspect ratio of microcracks (microcracks openings) that implies that the crack density parameter  (rather than porosity) is the proper microstructural parameter in which terms the elastic properties are to be expressed, and (II) the microcrack density  is relatively small, so that the non interaction approximation is legitimate.