PSI - Issue 77

João Nunes et al. / Procedia Structural Integrity 77 (2026) 593–600 Joa˜o Nunes et al / Structural Integrity Procedia 00 (2026) 000–000

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2.2. Tightening system and temperature monitoring setup

Type-K thermocouples and an HBM steel uniaxial strain gauge with nominal resistance of 120 Ω were used to val idate, respectively, the adequacy of the thermographic and DIC setups for monitoring both hydrogen cell temperature variations and the loosening of the tightening system’s bolts. Both sensors were installed in the tightening system’s shafts, as shown in Figure 2 b). National Instruments modules NI-9213 and NI-9235 were used to acquire, respec tively, both thermocouples’ and strain gauges’ data. Both modules were connected to a computer via an NI cDAQ 9171-chassis . Temperature and strain data were acquired at a rate of 100 Hz and 2kHz, respectively. A speckled pattern was applied in the upper shaft of the cell-tightening system, and a Basler acA5472-17um 20 MP USB camera with a 35 mm lens was used to capture images for 2D DIC at 1 fps. Initially, 3D DIC was tested; however, it was concluded that it was resulting in larger projection errors, likely due to the lack of su ffi cient synchronisation. Additionally, the principal strain was only required in a single direction for direct comparison with the uniaxial strain gauge. Simultaneously, an A6751 SC FLIR Camera with a spectral range of 3 to 5 µ m was used for temperature monitoring by acquiring images at 1 fps.

2.3. Performance Metrics of the Hydrogen Cell

Custom hardware was developed to acquire performance metrics of the hydrogen fuel cell. A MikroE Hall Current 4 module was used for current monitoring, while an INA219 integrated circuit was used for voltage monitoring. Both modules were connected to an Arduino Mega 2560 through the I2C communication protocol. Additionally, a 12 V DC motor was used to simulate di ff erent current demands. This circuitry was an important development, allowing both real-time monitoring of the hydrogen cell’s behaviour and the generation of performance data for the fuel cell.

3. Results and Discussion

3.1. Hydrogen Cell Normal Behaviour

As outlined in the introductory chapter, the first goal was to characterise the behaviour of the SENZA SZFC-100 PEM Hydrogen Fuel Cell model using thermocouples and strain gauges. After data treatment and post-processing, it was possible to obtain the results presented in Figure 3.

Fig. 3. Strain ( µε ) values (red), strain values after temperature compensation (blue) and Thermal Behaviour of the Hydrogen Cell During Short Term Operation

The black curve represents the temperature profile during short-term operation, showing an initial temperature rise followed by a decrease when the cooling fan is activated. The red curve represents the strain values after low pass filtering, while the blue curve shows the measured strain with temperature compensation. The temperature compensated strain values confirm that the shafts of the tightening system are subjected to tensile loading due to