# A Comprehensive Literature Review on Hydrogen Tanks: Storage, Safety, and Structural Integrity
## 5 Fundamental Issues
### Design Technology of Tanks
#### 5.2.2 Durability of Materials  
The durability of materials used in hydrogen storage tanks is another critical issue. The high-pressure environment, combined with hydrogen's tendency to embrittle certain metals and alloys, poses significant risks to the long-term integrity of the storage system [13]. Aluminum alloys applied to a liner material of a high-pressure hydrogen tank show several problems [168]. For automotive, but also in aerospace and marine sectors, the usage of Type III and especially Type IV hydrogen tanks instead of Type II is rapidly increasing due to the less presence of metals (Section 2.1). Composite materials, such as CFRP and GFRP, often address some of these issues due to their strength and lighter weight. However, these materials are also subject to wear and degradation over time, especially when exposed to repeated cycles of pressurization and depressurization. Environmental factors, such as exposure to moisture, extreme temperatures, and UV radiation, can further accelerate the degradation process. Moreover, the interactions between hydrogen and the materials at a microscopic level can develop micro-cracks and other structural weaknesses [20; 29; 132]. GFR is rapidly spreading in automotive [135], aerospace [41; 42] and aeronautical [45] fields. Ensuring that materials maintain their strength and integrity over the lifespan of the storage system requires ongoing research and development and rigorous testing under various operating conditions [163]. [PERSON] et al. [141] emphasized the necessity of accurate modeling techniques to predict material performance and longevity in high-pressure hydrogen storage applications. Temperature-dependent mechanical properties of HDPE used in high-pressure hydrogen storage vessels for automobiles revealed that Young modulus and tensile strengths of HDPE significantly increased with decreasing temperature [169]. [PERSON] et al. [170] presented a new method for accurately predicting burst pressures in high-pressure hydrogen tanks made of CFRP for fuel cell vehicles. It focuses on the complex, layered structure of the tanks, which includes carbon fiber bundles and matrix resin. The research utilizes cross-shaped specimens to mimic the conditions of the fiber bundles within the CFRP layers. The results show that the fracture processes of CFRP are significantly influenced by factors such as the strain rate dependency, the tensile-compression asymmetry of the resin, and the strength of the fibers. [PERSON] et al. [171] discussed the limitations and advancements in finite element modeling of Composite Pressure Vessels (CPVs), specifically those created using filament winding techniques. Traditional models based on CLT simplify the composite laminate as a stack of homogeneous plies with consistent thickness, orientation, and mechanical properties. For filament-wound CPVs, each layer is typically represented by two unidirectional plies with opposite fiber angles. However, this simplification does not accurately capture the real fiber geometry, where multiple plies may overlap, and fiber angles vary throughout the laminate. To address this, the research proposes an enhanced filament winding simulation that tracks the deposition of finite-width fiber bands, offering a more detailed representation of the actual fiber paths and overlaps. Transforming this detailed information into a CLT-based finite element model is challenging because it requires a complex mesh layout to represent each ply's unique angles and thicknesses accurately. The ultimate goal is to improve the safe and economical design of high-pressure hydrogen tanks for automotive applications. Despite their advantages, composite materials represent a big challenge, mainly linked to their thermal response [172; 173]. In fact, under fire conditions, the average failure pressure drops to 41.5 MPa, roughly one-third of its burst pressure [172]. This study's results underline that epoxy resin decomposition occurs between 100 \({}^{\circ}\)C and 600 \({}^{\circ}\)C, with four distinct reaction phases.