The influence of pressure reduction rates on the damage behaviour of hydraulic components

• Applicant: Professor Dr.-Ing. Marcus Geimer
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449676223

The proposed research project generates scientific findings on crack formation behaviour of a component in contact with hydraulic fluid at pressure reduction rates of up to 1,000,000 bar/s. The main objective of the project is to create an understanding of the effects that lead to premature failure due to high-pressure degradation rates. The current state of research is contradictory with its presented theories and results. The differences between the theories are investigated on a macro- and microscopic level. Thus, the hypothesis of the wedge effect of oil on components with pressure-induced deformation can be verified or falsified. Within this research project the theoretical fundamentals can be developed which lead to a damage theory for those hydraulic components.Based on own preliminary work, the effects occurring in the crack gap are simulated with the help of simulation methods and further analysed. The focus will be on the investigation of the crack closing behaviour during pressure reduction under consideration of realistic pressure reduction rates and crack geometries. As an object of investigation, crack growth is conceivable with the simplified geometry of a high-pressure measuring port of an axial piston pump closed with a threaded plug. A fluid-structure interaction model is used as a simulation approach, which can interact the occurring mechanical and fluidmechanical processes. With the aid of a fluid-structure interaction model and with extension of the same with regard to the closing behaviour of the gap, the modelling of crack propagation and the modelling of small gap heights, an understanding of the described crack behaviour is built up and damage mechanisms are investigated. By applying similarity theories, substitute systems (variation of geometry and oil viscosity) are derived, which show a physically comparable behaviour under congruent loading while reducing the required computing resources. The simulation results serve the derivation of the analytical fundamentals for a safe prediction of the component load as a function of the pressure drop rate. Furthermore, the simulation is able to identify the underlying damage mechanisms of accelerated crack growth.By exemplary pressure pulse tests of the considered components the parametrisation of the simulation model and the verification of the assumptions are verified. Component samples are prepared and pointed cracks are induced. The pressure pulses are generated in accordance with the loads occurring in the simulation, taking valid standards into account.

• DFG Programme: Research Grants