The most common studies in the literature are those analyzing fatigue life under cyclic loading for flax fiber-reinforced composites. A novel type of staple fiber yarn made from flax tow with almost unidirectional fiber orientation and a quasi-unidirectional fabric was developed for composite applications. Additionally, a hybrid material made of flax and glass was produced for a demonstrator component (an axle tie of a narrow-gauge railway). For such an application, the investigation of fatigue strength is of particular importance. Therefore, the fatigue behavior of flax, glass, and hybrid flax/glass composites was investigated in the high cycle fatigue range. A total of 10⁶ load cycles were carried out. From about 7³ to 8³ loading cycles, the flax laminate was found to have higher fatigue strength than the glass fiber-reinforced composite. The hybrid materials tend to show a higher fatigue strength than the glass type from approximately 2 × 10⁵ load cycles. Results based on a finite element method also demonstrate better fatigue properties at an increased number of load cycles for flax-based composites than the glass fiber-reinforced component. The flax/glass component’s fatigue strength ranged between the flax values and the glass fiber-reinforced composites. Overall, the hybrid material shows significantly better static bending and impact characteristics than flax and considerably better fatigue properties than the glass fiber-reinforced composite making the hybrid material attractive for an application in an axle tie.

For future launch vehicles, lightweight cryogenic pressure vessels are required for storage of the liquid hydrogen fuel. For their structural assessment, reliable and validated failure criteria are required. The present contribution provides an overview over the results of an ongoing research activity concerned with the validation of Puck’s composite failure criterion in the cryogenic regime. In a first step, an experimental investigation on unidirectionally fiber reinforced materials on coupon level has been performed. This test campaign has been complemented by tests on small breadboard-type specimens with an angle-ply stacking sequence. The specimens were featuring holes and tapered sections to provide stress gradients and concentrations. Test were performed at ambient temperature and in a liquid Helium environment. Puck’s failure criterion has been applied and found to provide a good prediction of first ply failure in both environments.