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

拟议的研究项目产生了关于在减压速率高达1,000,000巴/S的情况下与液压油接触的部件的裂纹形成行为的科学发现。该项目的主要目标是了解由于高压退化速率而导致过早失效的影响。目前的研究现状与其提出的理论和结果是相互矛盾的。从宏观和微观两个层面考察了这两种理论之间的差异。从而验证或证伪了油对受压变形构件的楔形效应假说。在本研究项目中，建立了液压元件损伤理论的理论基础，并在前期工作的基础上，利用仿真方法对裂纹缝隙中产生的损伤效应进行了模拟和分析。重点是在考虑实际减压率和裂纹几何形状的情况下，研究减压过程中的裂纹闭合行为。作为研究对象，裂纹扩展是可以想象的，简化的几何形状的轴向柱塞泵的高压测量端口关闭螺纹塞。采用流固耦合模型作为模拟手段，可以对发生的力学过程和流体力学过程进行相互作用。借助于流固耦合模型，并将其推广到缝隙闭合行为、裂纹扩展模型和小缝隙高度模型，建立了对所描述的裂纹行为的理解，并研究了损伤机理。通过应用相似理论，导出了替代系统(几何形状和油液粘度的变化)，它们在一致载荷下表现出物理上相似的行为，同时减少了所需的计算资源。模拟结果为作为压降速率函数的部件载荷的安全预测提供了分析基础。通过对所考虑的构件进行典型的压力脉冲试验，验证了模拟模型的参数化和假设的正确性。制备了成分样品，并产生了尖端裂纹。压力脉冲是根据模拟中发生的载荷生成的，并考虑了有效的标准。

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.