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

拟议的研究项目对在高达1,000,000 bar/s的减压速率下与液压流体接触的部件的裂纹形成行为产生科学发现。该项目的主要目标是了解高压降解率导致过早失效的影响。目前的研究状况与其提出的理论和结果是矛盾的。从宏观和微观两个层面考察了两种理论之间的差异。因此，可以验证或证伪油对压力变形部件的楔效应假设。在这个研究项目中，理论基础可以发展，从而导致这些液压元件的损伤理论。在自己前期工作的基础上，运用数值模拟方法对裂缝间隙产生的影响进行了数值模拟，并进行了进一步分析。重点将是在考虑实际减压率和裂纹几何形状的情况下，对减压过程中裂纹闭合行为的研究。作为研究对象，用螺纹塞封闭轴向柱塞泵高压测量口的简化几何形状可以想象裂纹的扩展。采用流固耦合模型作为仿真方法，可以将发生的力学过程和流固耦合过程相互作用。借助流固耦合模型，并对该模型进行了扩展，对裂缝闭合行为、裂纹扩展模型和小间隙高度模型进行了扩展，建立了对所描述的裂纹行为的理解，并对损伤机制进行了研究。通过应用相似理论，推导出替代系统（几何变化和油粘度），这些系统在相同载荷下表现出物理上的可比行为，同时减少了所需的计算资源。仿真结果为安全预测部件负荷随压降率的变化提供了分析基础。此外，模拟还能够识别裂纹加速扩展的潜在损伤机制。通过所考虑部件的示例性压力脉冲试验，验证了仿真模型的参数化和假设的验证。制备了零件样品，并诱发了尖裂纹。在考虑有效标准的情况下，根据模拟中发生的载荷产生压力脉冲。

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.