PSI - Issue 52

Yingwu Li et al. / Procedia Structural Integrity 52 (2024) 709–718 / Structural Integrity Procedia 00 (2023) 000–000 Author name

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Fig. 2. The Cumming plot of strain-frequency shift coe ffi cients under di ff erent temperatures in tensile experiment

Fig. 3. The Cumming plot of strain-frequency shift coe ffi cients under di ff erent fatigue cycles

The fatigue experiment involved continuous testing for 1,677,700 cycles at room temperatures. The Cumming plot of strain-frequency shift coe ffi cients under di ff erent fatigue cycles is presented in Figure 3. The x-axis of the plot represents di ff erent fatigue cycles, while the y-axis indicates the corresponding strain-frequency shift coe ffi cients. It is evident from the results that this coe ffi cient does not exhibit significant variation with an increase in fatigue cycles. Furthermore, the maximum mean di ff erence between test 1 at cycle 53,600 and other tests (less than 0.4 µε/ GHz) is lower compared to that observed in the tensile experiment under di ff erent ambient temperatures (less than 0.8 µε/ GHz). The strain-frequency shift coe ffi cients from nine tests conducted under room temperature in the three-point bending experiment are depicted in Figure 4. The x-axis represents T1 to T9, corresponding to test 1 to test 9, while the y-axis represents the strain-frequency shift coe ffi cients. Similar to the observations in the fatigue experiment, the strain frequency shift coe ffi cients in the three-point bending experiment exhibit a comparable level of stability, as the mean di ff erence between test 1 and other tests is less than 0 . 4 µϵ/ GHz.

2.2. The consistency assessment of strain-frequency shift coe ffi cient

In this section, the normality of the measurement of strain-frequency shift coe ffi cients presented in Section 2.1 is assessed firstly using the Kolmogorov-Smirnov (K-S) test. Widely recognized for testing the normality of mea surements, additional information on the K-S test can be found in Fu et al. (2015). The test results for the di ff erent