Fatigue behaviour and fatigue life calculation of the cast iron EN-GJS-600 under isothermal and thermo-mechanical loading

部件的重量优化和安全设计是乘用车和商用车行业的基本要求。在工作条件下，由于启动过程，气缸盖等部件会受到机械和循环热载荷的影响。在这种情况下，增加内部压力因此需要更高的疲劳强度。由于良好的机械和热性能的组合，铸铁适合满足这些要求。该研究项目的重点是目前用于商用车行业各种应用的球墨铸铁EN-GJS-600（ASTM 80-55-06）。除了个别微观结构和单调性能的疲劳行为在环境以及高温下将进行研究。机械应力-应变滞后、温度（仅在环境温度下）和电阻测量将用于验证疲劳行为。除了总应变控制应变增加和恒定振幅测试（测试频率为0.005 Hz至100 Hz）外，还将进行温升测试，以确定导致最大动态应变老化效应的温度。与传统的动态应变时效测定相比，这种短时间的过程导致实验时间的显着减少。此外，温度升高试验提供了根据变形速率和试验频率分别选择适当温度的可能性，用于进一步的应变升高和恒幅试验。在测量量的基础上，凯泽斯劳滕大学材料科学与工程研究所开发的基于物理的疲劳寿命计算方法PHYBAL将进行修改，以应用于总应变控制疲劳试验，此外还将考虑试验温度和频率的影响。根据前两年的结果，第三年将进行热机械疲劳试验。车辆发动机中出现的特征温度-时间函数将通过机械负载-时间函数同相和异相叠加（相移为180度）。为了可靠地确定车辆部件的尺寸，考虑复杂的热机械载荷条件的寿命计算是非常重要的。在第一年和第二年，PHYBAL应根据环境温度和高温下的总应变控制疲劳试验进行修改。在第三年，先进的短时程序将被修改，以满足额外的热机械载荷的具体要求。因此，必须考虑到，热载荷和机械载荷的分数不能简单地叠加，因为它们强烈地相互影响。

A weight optimised and safe design of components is a fundamental requirement of the passenger as well as commercial vehicle industry. Under service conditions components like cylinder heads are subjected to mechanical as well as cyclic thermal loadings due to start-up procedures. In this context, increasing internal pressures consequently request higher fatigue strength. Due to the combination of good mechanical and thermal properties cast irons are suitable to meet these requirements. This research project is focused on the nodular cast iron EN-GJS-600 (ASTM 80-55-06) currently used for various applications in the commercial vehicle industry. Besides the individual microstructure and the monotonic properties the fatigue behaviour at ambient as well as elevated temperatures will be investigated. Mechanical stress-strain hysteresis, temperature (only at ambient temperature) and electrical resistance measurements will be applied to characterise the fatigue behaviour. In addition to total-strain-controlled strain increase and constant amplitude tests with testing frequencies from 0.005 Hz to 100 Hz, temperature increase tests will be performed to determine the temperature leading to maximum dynamic strain-ageing effects. Compared to the conventional determination of dynamic strain-ageing, this short-time procedure leads to a significant reduction of experimental time. Furthermore, temperature increase tests offer the possibility to select appropriate temperatures as a function of the deformation-rate and testing frequency respectively for further strain increase and constant amplitude tests. On the basis of the measured quantities the physically based fatigue life calculation method PHYBAL developed at the Institute of Materials Science and Engineering at the University of Kaiserslautern will be modified for the application at total-strain-controlled fatigue tests additionally the influence of the testing temperature and frequency will be incorporated.Based on the results of the first two years, in the third year thermo-mechanical fatigue tests will be performed. A characteristic temperature-time-function emerging in vehicle engines will be superimposed in-phase and out-of-phase (with a phase shift of 180 Degree) by a mechanical load-time-function. For a reliable dimensioning of vehicle components a lifetime calculation which considers complex thermo-mechanical loading conditions is of high interest. In the first and second year, PHYBAL should be modified with respect to total-strain-controlled fatigue tests at ambient and elevated temperatures. In the third year, the advanced short-time-procedure will be modified to meet additionally the specific requirements of thermo-mechanical loading. Thereby, it must be taken into account that the thermal and mechanical loading fractions can not simply be superimposed because they strongly affect each other.