PSI - Issue 75

17

Fabrice Deleau et al. / Procedia Structural Integrity 75 (2025) 392–418 Emmanuel Persent, Deleau Fabrice, Guillaume Coudouel, Guillaume Perrin/ Structural Integrity Procedia (2025)

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Fig. 12: Instron 500 kN test bench with small sized prototype configuration

4.2. Prototype instrumentation Each small-sized i-Clip prototype was monitored using the following standard measurements: - The global axial force applied to the prototype. The force sensor has a range of 0 – 500 kN with an accuracy of ±2 kN. - Two extensometers (E1 on lug No 1 front of the assembly and E2 on lug No 2 at the rear) were used to evaluate the local strain near the lug contact surface (Fig. 12). Specific monitoring techniques were implemented to collect highly precise data regarding the prototype's condition. The main objective was to detect crack initiation and terminate the fatigue test upon its occurrence. An expert was tasked to observe and identify the crack initiation. To achieve this, the implementation of strain gauges was meticulously optimized. A set of 10 strain gauges (model Vishay 045PG) was employed to measure the axial strain above each male lug contact area (greater than 3 mm). This localization minimized stress gradients to ensure reliable correlation with finite element modelling. The maximum deviation observed was 7% for dynamic loading of 70 kN ± 50, with the average strain gauge readings at 0.075% ± 0.05 compared to numerical simulations at 0.079% ± 0.054%. Additionally, each strain gauge features a grid measuring 1.14 mm in length and 2.16 mm in width, while the total width of the 10-gauge set is 23.75 mm. The 1.14 mm length aligns with the principal strain direction, ensuring negligible strain gradient (approximately 0.01%). The 2.16 mm width allows for averaging the values within the measurement zone, considering the minimal or negligible gradient in the circumferential direction. The primary advantage of the strain gauge set is that all 10 strain gauges are pre-positioned by the manufacturer. This ensures perfect parallel alignment of the gauges and simplifies the operator's task of attaching the strain gauge set to the male part with minimal misalignment (Fig. 13).