Microstructure-sensitive fatigue lifetime assessment considering forming history effects

疲劳机理的准确建模是循环荷载作用下构件安全设计的关键因素。然而，在大多数制造过程中，材料的抗疲劳性是改变的。因此，该提案的目的是首次开发一个模型链，该模型链表达了制造过程对循环载荷下组件性能的影响。该模型链可以在工艺链方向上使用，也可以在工艺链方向上使用。因此，项目第一阶段的首要目标（目前正在申请资金）是在考虑所有制造过程引起的材料机械性能变化的情况下，为定义的部件疲劳性能找到最合适的工艺参数。在项目的未来阶段，期望的组件性能将转化为所需的微观结构配置，由原始材料在进入制造过程之前提供。该研究方案基于这样的研究假设：给定构件的疲劳强度及其整体完整性由其临界点的实际微观结构决定。实际的微观结构产生于部件在制造前的初始状态，并在制造和运行阶段演变。实际上，在微观和宏观尺度上，制造过程和部件性能的仿真模型已经存在。这些方法将进一步发展，以便为选定的演示示例量身定制，演示示例将通过包括固体前挤压（大块金属成形）和深滚（增量成形）在内的工艺链形成。在项目过程中，WZL将通过实验和相应的宏观建模，了解工艺参数与组件微观结构之间的相互依赖关系。在成形前以及工艺链的各个步骤中，对工件材料在初始状态下的计划全面表征将为微观力学建模和疲劳性能验证提供信息。IEHK的贡献将集中在微观结构特征和构件疲劳特性之间的桥梁，通过微观建模和模拟。微结构敏感疲劳建模方法将应用于整个制造过程的各个步骤，这些步骤由WZL执行的宏观模拟产生的边界条件确定。特别是，用数值定义的加载剖面进行模拟，将建立成形后残余应力的数据。循环拉伸压缩条件下的微结构敏感疲劳模拟将提供部件疲劳强度沿工艺链发展的信息。

The accurate modelling of fatigue mechanisms is a key factor for the safe design of components under cyclic loading conditions. However, the fatigue resistance of a material is altered in the course of most manufacturing processes. Therefore, the aim of the proposal is a first-time development of a chain of models which expresses the influence of manufacturing processes on the performance of a component under cyclic loads. This newly-developed model chain can be used in and against the process chain direction. As a consequence, the overarching objective of the first phase of the project (for which the funding is now requested) is to find the best suited process parameters for a defined component fatigue performance under consideration of all manufacturing process-induced changes of the material’s mechanical properties. In the future phase of the project, the desired component performance will be translated into a required microstructural configuration to be provided by the virgin material before it enters the manufacturing process. The research proposal is based on the research hypothesis that the fatigue strength of a given component and its overall integrity is governed by the actual microstructure at its critical points. The actual microstructure results from the initial state of the component before manufacturing and evolves during manufacturing and operation stages. Actually, models are already existing for the simulation of manufacturing processes and component performance on the micro and the macro scales. These approaches will be further developed in order to tailor them for the selected demonstrator example, which will be formed by means of a process chain including solid forward extrusion (bulk metal forming) and deep rolling (incremental forming). In the course of the project, WZL will gain knowledge on the interdependencies between the process parameters and the resulting microstructure of the component based on experiments and corresponding macro-modelling. The planned comprehensive characterization of the workpiece material in initial state before forming as well as during the individual steps of the process chain will give the information for micromechanical modelling and fatigue properties validation. The contribution of IEHK will focus on bridging between the microstructural features and component fatigue properties by means of micro-modelling and simulations. Microstructure-sensitive fatigue modelling approaches will be applied throughout the individual steps of the manufacturing process, which are identified by boundary conditions resulting from macro-simulations performed by WZL. In particular, the simulations with the numerically defined loading profiles of WZL will establish the data on residual stresses after forming. The microstructure-sensitive fatigue simulations under cyclic tension-compression conditions will give the information on how the fatigue strength of the component develops along the process chain.