Use of gamma-magnetic test methods for the evaluation of the damage evolution in metallic materials subjected to cyclic loading

为了实现金属材料或结构的（剩余）疲劳寿命计算的目标，必须确定并提供全面的信息。这些信息描述了微观结构和相关的材料机制，因此它们的非破坏性测定是一个重要方面，特别是对于正在使用的部件。除了外部和内部载荷和应变之外，化学成分和材料的条件特别确定并最终限制剩余使用寿命。使用传统的分析方法，这些影响因素通常只能破坏性地测量。原则上，磁性测量方法能够检测金属材料中的微观结构差异，这已被过去的许多研究所证明。然而，到目前为止，这种评价只能定性进行，这不可避免地需要进一步的系统研究作为定量表征的校准。这就是计划中的项目的用武之地，旨在为（剩余）疲劳寿命计算框架内的磁性测量方法以及金属材料的估计方法做出进一步贡献。在对非合金和低合金碳钢C22 R（SAE 1023）和20 MnCrS 5（SAE 5120）的研究中，将开发磁性能-应力-显微组织关系，并通过磁测量程序进行评估。用于研究的两种材料具有相当的化学成分，仅在锰和铬含量方面存在显著差异。此外，还将研究热处理对材料状态的影响以及叠加平均应力引起的载荷。这些待开发的参数将被整合到StressLife疲劳寿命计算方法中，并最终在上述研究材料上进行验证。除了通过应力-应变滞后测量以及温度测量和电阻测量来表征疲劳行为外，特别是巴克豪森噪声将被用作微磁方法，并且描述微观结构的参数将通过信号分析来导出。先前的研究表明，基于微磁学的方法原则上可用于表征疲劳行为。然而，为了进一步量化疲劳寿命计算中的结果，有必要对测量现象及其背后的材料机制进行系统研究。

In order to achieve the goal of a (residual) fatigue life calculation for metallic materials or structures, it is necessary that comprehensive information is determined and made available. This information describes the microstructure and the associated material mechanisms, whereby their non-destructive determination is an essential aspect, especially for components in service. In addition to external and internal loads and strains, it is the chemical composition and the material’s condition in particular that define and ultimately limit the residual service life. Using conventional analytical methods, these influencing factors can usually only be measured destructively. In principle, magnetic measuring methods are able to detect microstructural differences in metallic materials, which has been proven by numerous investigations in the past. However, so far this evaluation could only be carried out qualitatively, which inevitably requires further systematic investigations as calibration for a quantitative characterization. This is where the planned project comes in and is intended to make a further contribution to the improvement of magnetic measuring methods within the framework of (residual) fatigue life calculation as well as estimation methods for metallic materials. Within the investigations on the unalloyed and low-alloyed carbon steels C22R (SAE 1023) and 20MnCrS5 (SAE 5120), the magnetic property-stress-microstructure relationship is to be developed and made usable for the evaluation by means of magnetic measuring procedures. The two materials intended for the investigations have comparable chemical compositions which differ significantly only in manganese and chromium content. In addition, the influence of the condition of the material as a result of heat treatments as well as the load due to superimposed mean stresses will be investigated.These parameters to be developed will be integrated into the StressLife fatigue life calculation method and finally validated on the above-mentioned investigated materials. In addition to the characterization of fatigue behavior by means of stress-strain hysteresis measurement as well as thermometry and resistometry, the Barkhausen noise in particular will be used as a µmagnetic method and parameters describing the microstructure will be derived by means of a signal analysis. Prior investigations show that methods based on µmagnetics can in principle be used to characterize the fatigue behavior. For further quantification of the results in the context of a fatigue life calculation, however, systematic investigations of the measuring phenomena and the material mechanisms behind them are necessary.