PSI - Issue 80

Alessandro De Luca et al. / Procedia Structural Integrity 80 (2026) 403–410 D Alessandro De Luca / Structural Integrity Procedia 00 (2019) 000 – 000

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Figure 2. Average (a) silhouette score, (b) purity and (c) balance vs. excitation frequency for each path category. Solid lines represent feature triplets; dotted lines represent feature pairs. Colours indicate path categories.

Figure 3 presents the average contribution of each feature to the clustering quality metrics, aggregated over all path categories and frequencies for both pair and triplet combinations. The analysis shows that for silhouette score, features 5, 25, and 27 exhibited notably higher values, indicating a stronger capability to discriminate between clusters. In terms of purity, the separation of clusters appears relatively uniform across most features, with no pronounced differences between the majority of them. However, feature 28 distinctly stands out, achieving a significantly higher purity value. This suggests that feature 28 plays a particularly important role in producing clusters that closely align with the actual structural conditions, underscoring its potential relevance for damage identification. When considering balance, features 10, 14, 16, 25, 28, and 32 achieve particularly high values, indicating their effectiveness in generating cluster partitions with more uniform sizes.

Figure 3. Average (a) silhouette score (b) purity (c) balance per feature. The values represent the mean across all cluster in which each feature was involved, considering both pair and triplet combinations.

Figure 4 illustrates the overall distribution of silhouette score, purity, and balance values across all pair and triplet feature combinations. Despite the relatively low average values observed for the three indicators, the distributions reveal the existence of individual cases where clustering performance approached unity. These findings underscore the presence of feature combinations that, though rare, yield highly effective clustering outcomes, warranting further investigation.