Failure criteria for the prediction of compound journal bearing fatigue - Extension of the methodology considering microstructural effects, Project stage II

该项目的重点是描述白色金属合金在滑动轴承应用中的疲劳行为，这取决于微观结构。在项目的第一阶段，通过热弹性流体动力学（TEHD）和有限元（FE）模拟计算了复合轴颈轴承中的局部应力状态。通过失效假设，将多轴应力状态与部件疲劳强度相关联。实施的失效假设需要疲劳强度参数，这是通过实验确定的，用于评估所研究的白色金属合金。由于白色金属具有异质显微组织，由韧性固溶体基体与金属间相组成，导致沉淀硬化，显微组织对材料的动态强度有显着的影响。在材料和部件疲劳试验中都检测到了微观结构的这种影响。因此，只有当确定材料参数以计算疲劳极限的样本微观结构与待评估部件的微观结构相同时，才有可能进行充分的寿命预测。因此，微观结构对宏观强度的影响将在第二个项目阶段进行研究和描述。在微观力学领域，代表性体积元法（RVE）是一种公认的将微观特征与宏观材料性能联系起来的工具。为了计算RVE，将白色金属的显微照片转换为网格化的有限元模型。关于边界条件和相的特定材料模型，RVE暴露于操作负载。这是针对关键参数（诸如相分数、尺寸和分布）不同的不同RVE进行的。通过均匀化步骤，关于有效材料性质的宏观响应可以从各个相的材料性质导出。通过考虑细观模拟和均匀化研究的结果，宏观有限元模型可以调整到局部有效材料行为。通过这种方式，可以计算应力状态作为有效微观结构的函数。此外，影响宏观静态和动态强度的关键参数可以通过全面的数值案例研究来确定。这是通过将RVE中的应力和应变集中与外部载荷相关联来完成的，这使得能够确定复合滑动轴承的损伤标准。数值结果的验证是通过实验材料和组件测试。最后，个别步骤的结果被用来提高寿命预测的方法，在第一个项目阶段开发的轴颈轴承，考虑有效的材料参数作为微观结构的函数。

Focus of this project is the description of the fatigue behaviour of white metal alloys in plain bearing applications depending on the microstructure.In the first stage of the project, the local stress state in a compound journal bearing has been calculated by thermo-elastohydrodynamic (TEHD) and finite element (FE) simulations.The multiaxial stress state has been related to the component fatigue strength by means of failure hypotheses. The implemented failure hypotheses require fatigue strength parameters, which have been determined by experiments, for the evaluation of the investigated white metal alloys.As white metals have a heterogeneous microstructure, composed by a ductile solid solution matrix with intermetallic phases causing precipitation hardening, the microstructure has significant influence on the dynamic strength of the material. This influence of the microstructure has been detected in both material and component fatigue tests. Hence, an adequate lifetime prognosis is only possible, if the microstructure of the specimens, from which material parameters are determined to calculate the fatigue limit, is identical to the microstructure in the component to be evaluated. Therefore, the influence of the microstructure on the macroscopic strength will be examined and described in the second project stage.In the field of micromechanics the method of representative volume elements (RVE) is an established and accepted tool for linking microscopic features with macroscopic material properties. In order to calculate RVE, micrographs of white metal are converted into meshed FE models. Regarding the boundary conditions and specific material models of the phases, the RVE is exposed to the operational loads. This is done for different RVE that vary in key parameters such as phase fraction, size and distribution. By the step of homogenization the macroscopic response regarding effective material properties can be derived from material properties of the individual phases. By considering the findings of the mesoscopic simulations and homogenization studies the macroscopic FE model can be adjusted to the local effective material behavior. In this way, the stress state can be calculated as a function of the effective microstructure. Furthermore, key parameters affecting the macroscopic static and dynamic strength can be identified by comprehensive numerical case studies. This is done by correlating stress and strain concentrations in the RVE with external loads, which enables the determination of a damage criterion for composite plain bearings. The validation of the numerical results is done by experimental material and component tests. Ultimately, the results of the individual steps are used to enhance the methodology of lifetime prediction of journal bearings developed in the first project stage by considering effective material parameters as a function of the microstructure.