Project description:

Hydraulic components are often exposed to extreme loads during operation. Pressure gradients of up to 20,000 bar/s can occur when the tip of a wheel loader bucket hits a stone during penetration into a pile. If such loads occur repeatedly, this can lead to failure of the mobile hydraulics, especially if the fatigue strength of the materials is exceeded.

Crack growth in hydraulic components under the influence of high pressure reduction rates is at the centre of the investigation. If oil penetrates an existing crack, this leads to an increased pressure load on the crack flanks. Compared to a component without a crack, this causes increased mechanical stress. If the pressure then drops rapidly, the oil cannot escape completely from the crack and remains inside. The result is the so-called wedge effect: the oil remaining in the crack indirectly connects the crack flanks and prevents a complete return to the original state. This phenomenon is known as oil-induced crack closure. It is unclear whether the permanent mechanical deformation of the components is due to the wedge effect of the oil or to residual plastic deformation of the crack environment and how these two phenomena can be distinguished from each other.

As part of the project, an existing simulation model of fluid-structure interaction is being further developed. This includes a more detailed flow simulation that takes into account both the macroscopic crack geometry and the surface roughness of the crack. In addition, a simplified finite element model is expanded to a complete structural simulation. It is combined with a plastic yield strip model in order to realistically model the plastic deformations in the area of the crack tip and their development as the crack progresses. The knowledge gained from this should improve the understanding of the effects that lead to premature failure due to high pressure degradation rates and create a basis for reliably predicting such damage mechanisms based on the load profile.

The research project is being carried out in close collaboration with the Institute of Fluid Power Drives and Systems at RWTH Aachen University, the Fraunhofer Institute for Mechanics of Materials IWM and the Institute for Applied Materials - Reliability and Microstructure at the Karlsruhe Institute of Technology.