Microstructure-sensitive fatigue lifetime assessment considering forming history effects

疲劳机理的准确建模是循环载荷作用下构件安全设计的关键因素。然而，材料的疲劳抗力在大多数制造过程中都会发生变化。因此，该提案的目的是首次开发一系列模型，该模型链表示制造过程对部件在循环载荷下的性能的影响。这种新开发的模型链可以用于流程链方向的正反向使用。因此，该项目第一阶段(现已申请资金)的首要目标是在考虑所有制造工艺引起的材料机械性能变化的情况下，为确定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，所需的部件性能将转化为原始材料在进入制造过程之前所需的微结构配置。该研究建议基于这样的研究假设，即给定部件的疲劳强度及其整体完整性由其临界点的实际显微组织决定。实际显微组织由制造前部件的初始状态产生，并在制造和操作阶段演变。事实上，已经存在用于在微观和宏观尺度上模拟制造过程和部件性能的模型。将进一步开发这些方法，以便为选定的示范实例量身定做，该实例将通过包括固态正向挤压(散装金属成形)和深轧(增量成形)在内的工艺链来形成。在项目过程中，WZL将在实验和相应的宏观建模的基础上，了解工艺参数和由此产生的部件微观结构之间的相互依赖关系。在成形前的初始状态以及工艺链的各个步骤中，对工件材料的有计划的综合表征将为微观机械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部件疲劳特性之间的桥梁上，通过微观建模和模拟。微结构敏感的疲劳建模方法将应用于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WZL载荷分布进行的模拟将建立成形后残余应力的数据。循环拉伸-压缩条件下的微观组织敏感疲劳模拟将提供构件疲劳强度如何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.