The determination of the optimum autofrettage pressure enables a clear improvement of the fatigue life for an internally highly pressurized component. The autofrettage process induces residual compressive stress after the release of a single static overload pressure, leading to plastic deformation at the inner wall whereas the outer part is only elastically stressed. This autofrettage pressure is clearly above the subsequent pulsating operating pressure range. Due to the complex geometry of the aluminium valve body, a detailed elastic–plastic finite element analysis is used to determine the critical area and the optimum autofrettage pressure. Based on an experimental stress–strain curve, three important load steps are simulated in a non‐linear way. The FKM guideline is used to assess fatigue life and crack initiation with detailed subsequent experimental verification. Even if small cracks occur, residual compressive stresses prohibit crack growth (nonpropagating crack), which can be analytically verified by fracture mechanical considerations (crack closure effect).

Stress relaxation describes the reduction of stress under static or cyclic loading at a constant strain level. Several processes induce intentionally residual stresses, for example, autofrettage of thick-walled pressurized tubes to improve their fatigue life. This well-known process induces residual compressive stresses at the critical inner surface by using a single static but controlled overloading internal pressure. Relaxation of residual stresses due to cyclic loading in service would endanger the effectiveness of autofrettage and could finally lead to unexpected fatigue failure. In this study, strain-controlled experiments up to 500,000 load cycles and amending nonlinear finite element simulations were done for the aluminum alloys EN AW 6061 T6 and EN AW 6082 T6 to study potential cyclic stress relaxation in four-point bending tests after controlled single static plasticization for residual stress generation. This analysis identifies almost stable residual stresses for both materials under different cyclic strain-controlled load levels.

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This study introduced a fatigue-based approach to design and implement an indicator channel into an in-tank hydrogen valve. It was aimed at providing a mean to point out multiple early valve's damages. To achieve the goal, the study was proposed to handle via three main phases. They included (i) the risk point determinations, (ii) the new valve design and the crack nucleation life estimations, as well as (iii) the simplified crack growth analyses. The obtained results firstly highlighted the construction of the test channel (TC), whose branches were located close to the predicted damage's sites. The damages could be identified either when a crack reaches the TC (then forms a leakage) or indirectly via the crack propagations’ correlation. The results also pointed out that the TC-implemented valve could perform as similarly as the non-TC one in the non-treated condition. More importantly, this new structure was proved to have a capacity of satisfying the required minimal life of 1.5E5 cycles, depending on the combined uses of the specific material and the pre-treatment, among those considered. In addition, the results emphasized the complexity of the TC that could not be formed by the traditional manufacturing process. Hence, direct metal laser sintering was proposed for the associated prototype and the final TC was issued based on the fundamental requirements of the technique. Finally, it was suggested that practical experiments should essentially be carried out to yield more evidence to support the demonstrated results.