Issue 78

C. Vendittozzi et alii, Fracture and Structural Integrity, 78 (2026) 519-540; DOI: 10.3221/IGF-ESIS.78.30

event-wise quantitative descriptors for Datasets A and B are summarized in Tables 2 and 3, which condense the ridge-based and band-limited spectral information into compact event-level descriptors. These tables are intended to support comparison among sensors, events, and the two representative datasets; they are not used here to define damage thresholds, hard-landing classes, or statistically validated repeatability over a population of landings.

Band RMS [ ] 8.86E-07 8.42E-07 1.03E-06 3.84E-06 1.15E-06 1.09E-06 1.03E-06 3.29E-06 2.02E-06 1.63E-06 1.09E-06 4.56E-06 Band RMS [ ] 7.67E-07 9.41E-07 1.09E-06 3.77E-06 1.38E-06 1.33E-06 1.03E-06 4.75E-06 1.16E-06 1.06E-06 7.11E-07 2.26E-06

Ridge median (Hz)

Ridge IQR (Hz)

RMS-dominant band

Ridge persistence in RMS dominant band (%)

Dataset Sensor Event

A A A A A A A A A A A A

S1 S2 S3 S4 S1 S2 S3 S4 S1 S2 S3 S4

1 1 1 1 2 2 2 2 3 3 3 3

18.10 18.10

9.30 1.00 1.50 4.40 0.00 0.00

20–60 Hz 20–60 Hz

5.10 0.00

149.40 429.20

120–220 Hz 350–500 Hz

74.60 83.10

10.30 18.10

20–60 Hz 20–60 Hz

5.10 1.70

148.90

128.90 412.60

120–220 Hz 350–500 Hz

59.30 33.90 27.60 44.80 27.60 50.00

18.60 18.60 18.80 35.60

9.30 1.50

20–60 Hz 20–60 Hz

145.00 415.00

120–220 Hz 350–500 Hz

223.60

Table 2: Dataset A. Quantitative event-based descriptors of the dominant spectral response. The RMS-dominant band is the predefined frequency interval with the largest band-limited RMS contribution within the event-centered window. Ridge persistence indicates the percentage of accepted ridge points falling inside that band.

Ridge median (Hz)

Ridge IQR (Hz)

RMS-dominant band

Ridge persistence in RMS dominant band (%)

Dataset Sensor

Event

B B B B B B B B B B B B

S1 S2 S3 S4 S1 S2 S3 S4 S1 S2 S3 S4

1 1 1 1 2 2 2 2 3 3 3 3

18.10 18.60

8.90 1.00

20–60 Hz 20–60 Hz

3.50 3.50 7.00

150.40 427.70

132.80

350–500 Hz 350–500 Hz

4.20 8.80 0.50 2.40 0.50 0.70 1.00

100.00

18.60 18.60

20–60 Hz 20–60 Hz

3.40 3.40

149.90 426.80

132.70

120–220 Hz 350–500 Hz

52.50

100.00

18.60 18.60 18.60 18.60

20–60 Hz 20–60 Hz 20–60 Hz

4.20 0.00 0.00

415.00

350–500 Hz

37.50

Table 3: Dataset B. Quantitative event-based descriptors of the dominant spectral response. The RMS-dominant band is the predefined frequency interval with the largest band-limited RMS contribution within the event-centered window. Ridge persistence indicates the percentage of accepted ridge points falling inside that band. The quantitative results indicate that the dominant spectral content is strongly sensor-dependent within the two analyzed records. In Dataset A, sensors S1 and S2 are primarily associated with the low end of the analyzed band, with ridge medians concentrated in the approximate 10–20 Hz region. By contrast, sensor S3 emphasizes a recurring mid-frequency family near 150 Hz in Events 1 and 2, while sensor S4 emphasizes a high-frequency family near 429 Hz in Event 1. The band-limited RMS descriptors support the same sensor-dependent structure, with the RMS-dominant contribution for S3 occurring in the 120–220 Hz band and that for S4 occurring in the 350–500 Hz band. Dataset B shows recurrence of comparable sensor dependent frequency families, together with redistribution of spectral dominance relative to Dataset A. Sensors S1 and S2

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