PSI - Issue 68

J.C. Gomez-Mancilla et al. / Procedia Structural Integrity 68 (2025) 1208–1215 Gomez-Mancilla J / Structural Integrity Procedia 00 (2025) 000–000 St

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a) { SDI } k (3) Briefly, onset damage exists whenever a damage index vector, transformed by any BSFI formulae, { SDI } k t > 0, means that damage has started, see Gomez-Mancilla (2024). 5. 3 rd Criterion for Damage Onset Fig. 4a (up RHS). VHCF response is in the usual axial direction of the specimen, which is expected in current VHCF experiments. Contrast both signals simultaneously acquired; the axial natural frequency of the system dominates the response. Notice that the axial excitation ends at number 282,000 data, which yields both responses to practically collapse. Fig. 4b. Lower LHS, segments 140 to 145. Transverse response of the VHCF test implementing recommendation: the transverse direction -Flex of the tip of the specimen is measured. Great contrast when comparing vs. the axial response; regardless of the Flex having a lower amplitude, it contains much more helpful information, such as several amplitude trends and a complex and rich frequency spectrum. In the author's method the amplitudes are less important vs. obtaining modal-frequency-other spectra. I found several instances of damage onset caused by persistent slip bands (PSB) and micro-crack coalescence. t > 0, for any m mode

Figs. 4. LHS contrast time axial (upper) and flex (lower) simultaneously responses. On the RHS, the 2nd larger bending response (Ch2) vs. time-segments illustrates several frequency drops, three additional damage occurrences at the beginning, coherent result with Figs. 2b and 5. The third criterion is based on observing limit values of bending response amplitudes where sudden significant amplitude increases higher than 30%; increasing amplitude trends indicate that probe damage of some kind has occurred. Bending response amplitude increases are so easy to detect, i.e., compare axial (upper Fig. 4a) Figs. 4c at the RHS, shows the second larger bending response frequencies reiterating the same damage segments as the NAD and First criterion do, nonetheless, the comparison adds three more drops, where additional potential damage might occur. Fig. 5 compares peaks of the NAE criteria using two versions of it vs. amplitude valleys of the specimen’s bending response as the vertical lines show coincide in what follows. A vibration interpretation goes that, when the principal amplitude frequency component diminishes, as in valleys, the vibratory energy transfers to other nonlinear frequency components, i.e., amplitude valleys coincide with β’, β’’ criteria peaks. As flexing Figs. 2b and 5 indicate, it is likely that the first damage occurred at the test first stages; and of course, nearly at the end of the test, Fig. 4b.