On the frequency dependency of fatigue damage caused by viscous fluid-structure interaction in hydraulic components

Experimental fatigue tests have been conducted for decades to study the lifetime of hydraulic components. Nevertheless, predicting the lifetime of hydraulic components remains difficult. For a quick market entry, test periods have to be short, and tests are often done under constant cyclic loading at high frequencies. The damage accumulation of hydraulic components, however, depends on the temporal load profiles, as viscous fluids introduce a time dependency. As a result, high pulsation frequencies alter the damage accumulation, which can result in misleading and inapplicable lifetime results. Previous studies have shown a significant difference in crack growth and lifetime when specimens have been submerged in pressurized oil. Despite the similarities between these experiments and hydraulic systems, the frequency dependency of fatigue damage in hydraulic components and the corresponding fluid-structure interaction in fatigue cracks have not yet been quantified. A one-dimensional numeric flow model in connection with a finite-element structural analysis was used to simulate the fluid flow and the crack opening. Based on the resulting stress amplitudes, the expected crack growth was predicted and compared to experimental data. ... mehrThe experiments show that the temporal load profile is critical to ensure equivalent damage accumulation in fatigue experiments. Otherwise, premature component failures can occur, and a large safety margin has to be applied.