Dynamic fluid simulation of hydraulic oil flow inside fatigue cracks during transient loads

Fatigue damage plays an important role in mobile hydraulics as all components are subject to varying and highly transient loads. Transient loads lead to complex damage accumulation processes and, thereby, difficulties in design and testing. Estimation of fatigue damage during complex load cycles allows efficient design and maintenance cycles, besides being the groundwork for real-time damage monitoring in the future.
The interaction between pressurized fluid and crack faces is supposed to have a significant effect on the fatigue crack growth of hydraulic components. It prevents crack closure and contact of the crack faces during unloading.
In this paper, we introduce a simplified simulation for the fluid flow in narrow cracks. Coupling the fluid simulation with a mechanical solver to account for elastic pressure-related deformation is difficult in terms of numeric stability. Instead of artificially modifying the fluid properties to increase the dynamic dampening effects of the fluid, we simplify the mechanical deformation matrix and introduce damping to the mechanical deformation to improve the overall solution stability. Our results show that dynamic effects do influence the fluid flow inside cracks and, thereby, fatigue crack growth.