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（残余）疲劳寿命计算的目标，有必要确定和提供全面的信息。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必不可少的方面，特别是对于正在使用的部件。除了外部和内部载荷和应变外，化学成分和材料的状况特别决定并最终限制了剩余使用寿命。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的微观结构差异，这已经被过去的许多研究证明。然而，到目前为止，这种评价只能定性地进行，这不可避免地需要进一步的系统调查作为定量特征的校准。这就是计划中的项目进入的地方，旨在为改进（残余）疲劳寿命计算框架内的磁测量方法以及金属材料的估计方法做出进一步的贡献。在对非合金和低合金碳钢C22R （SAE 1023）和20MnCrS5 （SAE 5120）的研究中，将开发磁性能-应力-显微组织关系，并使其可用于通过磁性测量程序进行评估。用于研究的两种材料具有相似的化学成分，仅在锰和铬含量上有显着差异。此外，还将研究热处理对材料状况的影响，以及由于叠加平均应力而产生的载荷。这些待开发的参数将集成到应力-寿命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-应变迟滞测量以及温度测量和电阻测量来表征疲劳行为外，还将特别使用巴克豪森噪声作为微磁方法，并通过信号分析推导出描述微观结构的参数。先前的研究表明，基于微磁的方法原则上可以用来表征疲劳行为。然而，为了在疲劳寿命计算的背景下进一步量化结果，有必要对测量现象及其背后的材料机制进行系统的研究。

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.