Use of non-destructive testing methods in a new one-specimen test strategy for estimating fatigue data

本研究计划的目的是利用无损检测方法的潜力，测量技术的数字化以及信号处理，并将其与新的单试件测试策略相结合，以便在减少实验努力和成本的同时获得有关疲劳行为的信息。因此，如果有可能通过数据分析分离几种材料效应，并将其用于基于单个试样结果的疲劳寿命计算，那么结果可能不仅相对于传统的测定S，N数据具有相当大的优势，而且对于已建立的短期程序也具有相当大的优势。在新的疲劳寿命计算方法SteBLife（阶梯杆疲劳寿命评估）中，为了通过应用不同的无损检测技术来检测材料的局部响应，使用了具有多个量规长度的阶梯试样几何形状。首先，对C45E/SAE1045钢试样的初步研究已经显示出非常有希望的结果。在这些研究中，材料响应是通过红外相机测量的，在本研究计划的框架内，将通过额外的热电偶测量来加强，并扩展到磁测量方法。与传统方法相反，样品不是用电磁铁或永磁体磁化，而是通过施加恒定/交流电流或电压来产生特定微观结构相关的磁场。测量信号将根据具体特征进行分析；特别是，使用COMSOL等商业模拟软件解决方案对测量信号进行模拟，可能会对结果的理解和解释做出重大贡献。对C20E、C45E和42CrMo4非合金钢和低合金钢分别在正火和一种市售调质条件下进行实验研究、模拟和信号分析。

The aim of this research proposal is to use the potential of a non-destructive testing methods, the digitalisation of the measurement techniques as well as signal processing and to combine this with a new one-specimen test strategy in order to achieve a significant gain in information concerning the fatigue behaviour with a simultaneous reduction of experimental effort and costs. The result might be therefore not only a considerable advantage with respect to conventional determined S,N data, but also to established short-term procedures, if it is possible to separate several material effects by means of data analysis and to use this for fatigue life calculations based on the results of one single specimen.Within the new fatigue life calculation method SteBLife (Stepped Bar Fatigue Life Evaluation) a stepped specimen geometry with several gauge lengths is used in order to detect the local material responses through the application of different NDT techniques. First preliminary investigations for specimens from the steel C45E/SAE1045 have already shown very promising results. Within that investigations, the material response was measured by means of an infrared camera, which is to be intensified by additional thermocouple measurements in the framework of this research proposal and also extended to magnetic measurement methods. Contrary to the conventional approach, the specimens are to be magnetized not with electric or permanent magnets, but by means of an applied constant/alternating current or voltage to generate a specific microstructure related magnetic field. The measuring signals will be analysed in terms of specific features; in particular, the simulation of the measurement signals using commercial simulation software solutions like COMSOL might give a significant contribution to the understanding and interpretation of the results. The experimental investigations, simulations and signal analysis will be made on/for unalloyed and low alloyed carbon steels C20E, C45E and 42CrMo4 in normalized and one commercially available quenched and tempered condition each.