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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process is fully clean, environmentally friendly and sustainable, which has driven the growth of this field in recent years [1]. Typically, a PEMFC stack consists of bipolar plates, current collectors, gas di ff usion layers (GDL) and membrane electrode assemblies (MEA), which are symmetrically assembled. Gaskets are typically included for improved sealing. All these components are supported by two rigid end plates commonly referred to as the tightening system, as shown in Figure 1 [1, 2, 3]. Given that a single fuel cell is only capable of generating a potential of about 1V at open circuit, it is common to find many individual cells in series or parallel to increase power generation capabilities, resulting in a so-called fuel stack [2].

Fig. 1. Schematic of a single polymer electrolyte membrane fuel cell.

The literature highlights the importance of tightening systems in fuel stacks, which determine both the performance and the durability of the cell [1, 2, 4, 5, 6]. The plates of the tightening system are placed on both sides of the fuel cell stack, providing structural integrity and ensuring proper contact between layers [6]. The application of a suitable clamping load generally leads to a higher electronic and thermal conductivity in the MEA, thus improving cell performance by reducing contact resistance and some of the losses in electrical and thermal resistance within the cell [1, 2]. In turn, if the clamping load is applied excessively, it can reduce the permeability and porosity of the GDL, a ff ecting its properties, such as hydrophobicity, and impeding the transfer of reactants from the channel to current collectors, thus degrading cell performance [1, 2]. For these reasons, an optimal clamping force should establish a balance between the electrical resistance and the gas transportation between layers [3]. [9] et al report that approximately 59% of the total power loss in a PEMFC can be attributed to a non-proper contact between bipolar plates and gas di ff usion layers, highlighting the relevance of the tightening system in these devices. Although the importance of this system is well recognized in the literature, most of the studies on structural mon itoring of hydrogen cells focus mainly on optimizing clamping loads of the tightening system during the design and assembly stages [8, 10, 11, 12, 13, 14]. However, during fuel cell operation, di ff erent stresses caused by thermal and vibrational loads can arise and cause the loosening of the tightening system [1]. To enable preventive maintenance and enhanced performance, monitoring should be continuous throughout the cell’s lifecycle, rather than limited to the design stages. Hydrogen cells’ temperature is also a relevant parameter that significantly a ff ects hydrogen cells’ performance [1, 7, 16, 17, 18]. Since half of the released energy is transferred to thermal energy in the stack during its operation, a significant temperature asymmetry gradient can be generated in the PEMFC if proper thermal management is not achieved [7]. An increase in fuel cell temperature can lead to membrane dehydration and poor catalyst performance, while a decrease can cause water condensation, which also negatively a ff ects system performance [1, 7]. Based on this problem statement, three main objectives were defined for this study. The first goal was to obtain a global understanding of the behaviour of a commercially available fuel cell. To that end, strain and temperature in the shafts of the cell tightening system were monitored with strain gauges and thermocouples, respectively. By validating the locations suitable for strain and temperature monitoring, this step will enable the achievement of the ultimate