PSI - Issue 72

Niki Tsivouraki et al. / Procedia Structural Integrity 72 (2025) 141–148

147

(a)

(b)

Fig. 7. Residual force versus (a) DI (experimental and numerical) and (b) normalized frequency ratio ( f = 3.5 kHz) (experimental and numerical).

Similarly, in Fig. 8, residual fatigue life is plotted against normalized frequency for the tests and the model. The observed deviation between the two methods is explained in the previous paragraph. Using both curves (trendlines), residual fatigue life of the coupons can be estimated using the normalized frequency.

Fig. 8. Residual fatigue life versus normalized frequency ratio (experimental and numerical) of thermoplastic coupons.

6. Conclusions This study proposes a methodology for estimating the residual fatigue life and strength of thermoplastic coupons by leveraging their random vibration characteristics. Initially established through experiments and later replicated numerically, the methodology incorporates tensile and fatigue tests alongside random vibration assessments. Furthermore, C-scan tests are utilized to establish a correlation between frequency and progressive fatigue damage. A corresponding model has been developed for each mechanical and vibration test. The main conclusions that can be drawn from the study are:  Experimental measurements, numerical predictions, and empirical calculations of residual frequency degradation show significant differences, primarily due to the idealized conditions of the numerical model.  Both experimental and numerical approaches can estimate the residual fatigue life and strength of thermoplastic coupons. The experimental method relies solely on frequency measurements, while the numerical approach operates independently of physical tests.