PSI - Issue 52

Yingwu Li et al. / Procedia Structural Integrity 52 (2024) 709–718

711

Author name / Structural Integrity Procedia 00 (2023) 000–000

3

Fig. 1. The Cumming plot of strain-frequency shift coe ffi cients under di ff erent temperatures in tensile experiment

Table 1. The experiment details in strain measurement. Test scenarios Dimensions / mm

Temperature ◦ C

Load configuration

Test quantities

Tension Fatigue

200 × 50 × 3.2 200 × 50 × 3.2 300 × 225 × 3.2

0-10kN

-30 ∼ 70 Room

12 13

0-3kN / 5Hz / 1677700 cycles

Three-point bending

0-90N

Room

9

a tensile experiment using distributed fiber optic sensing is demonstrated in Figure 1. In the depicted subfigure at the bottom-right of Figure 1, 1000 measurement values of strain gauge and SMF sensor (GHz) during the tensile experiment are presented. The blue line in the subfigure represents the strain gauge measurement in units of µε ,while the red line represents the SMF sensor measurement in units of GHz. From these measurements, points between 601 to 900 are selected to calculate the strain-frequency shift coe ffi cients, which are depicted in the top-right subfigure. The similar procedure is applied to calculate the temperature-frequency shift coe ffi cient in temperature experiments. In this case, the reference temperature is readily obtained from the environmental chamber, eliminating the need for additional temperature sensors. In this section, the results of this coe ffi cient obtained from a tensile test, a fatigue test, and a three-point bending test are utilized. Detailed experimental information can be found in Table 1. The specimens used in these experiments are composed of the same composite material, namely TENAX @ − E IMS65 E23 24K, and have a consistent layout of [45 / 90 / − 45 / 0 / 45 / 0 2 / − 45] s . And the SMF sensors coated with polymer were model SM1500(9 / 125)P, manu factured by FIBERCORE are adopted in these experiments. The polymer coating exhibits notable features, such as high temperature survival, bend insensitivity, and enhanced photosensitivity, making it highly desirable for distributed strain sensing applications. All distributed sensing data were obtained using the ODiSI-B system, manufactured by LUNALtd. The tensile experiment was conducted at various ambient temperatures, ranging from -30 to 70 ◦ Cwith a 5 ◦ Cstep. The Cumming plot Ho et al. (2019) of strain-frequency shift coe ffi cients under di ff erent temperatures is depicted in Figure 2. The x-axis represents di ff erent tests conducted under di ff erent temperatures, while the y-axis indicates the corresponding strain-frequency shift coe ffi cients. The results obtained at 30 ◦ C (room temperature) serve as the reference for calculating the di ff erences between di ff erent tests, and these di ff erences are shown at the bottom of Figure 2. Observations reveal that the strain-frequency shift exhibits slight variations with changes in ambient temperature, particularly when the ambient temperature falls below − 20 ◦ C or exceeds 70 ◦ C.