The external piping system which connects power devices, valve control devices, actuators, etc. is an essential system on the aero engine. Under the combined effects of high fluid pressure and external vibration, multiaxial fatigue failure is the main factor that seriously affects the safety of the piping system. The objective of this paper is to establish the multiaxial fatigue life model for the typical welded fuel pipe of the piping system by combining fatigue testing, simulation and theoretical analysis which is of great guiding significance for the engineering application of the piping system. Firstly, the fatigue limits of welded fuel pipes under no and 13.5 MPa internal pressure are obtained by rotational bending fatigue tests using the up-and-down method. Three additional stress levels of rotational bending fatigue tests under no internal pressure are supplemented and then the S-N curve is further obtained by the group method. Since the corresponding fracture surface of the specimens locates at the weld toe near the fixed end, peak stress method is adopted to evaluate the fatigue performance of the weld toe on the pipe specimens. In addition, by comparing the fatigue limit with no and 13.5 MPa internal pressured pipes, it is obvious that the equivalent uniaxial stress corrected by Gerber formula is not applicable for the multiaxial fatigue condition which is caused by the combined effect of fluid pressure and displacement load. The local stress concentration factor caused by the weld toe is determined and based on Findley critical plane model, the multiaxial fatigue life model is established which simultaneously takes the local stress concentration effect, mean stress effect and multiaxial stress effect into consideration. The results of rotational bending fatigue tests under 13.5 MPa internal pressure are within the triple error dispersion band and the accuracy of the proposed life model are verified.

中文翻译：

---

焊接燃油管的疲劳性能测试和寿命预测


连接动力装置、阀门控制装置、执行机构等的外部管路系统是航空发动机上必不可少的系统。在高流体压力和外部振动的共同作用下，多轴疲劳失效是严重影响管道系统安全的主要因素。本文的目的是通过疲劳试验、仿真和理论分析相结合，建立管道系统典型焊接燃油管的多轴疲劳寿命模型，对管道系统的工程应用具有重要的指导意义。首先，通过上下法旋转弯曲疲劳试验，获得了无内压和13.5MPa内压下焊接燃油管的疲劳极限。补充了无内压下旋转弯曲疲劳试验的三个附加应力水平，然后通过成组法进一步得到S-N曲线。由于试件相应的断裂面位于固定端附近的焊趾处，因此采用峰值应力法评价管材试件焊趾的疲劳性能。另外，通过与无内压管道和13.5MPa内压管道的疲劳极限对比，可以看出，Gerber公式修正的等效单轴应力不适用于由流体压力和位移载荷共同作用引起的多轴疲劳工况。 。确定焊趾引起的局部应力集中系数，基于Findley临界面模型，建立同时考虑局部应力集中效应、平均应力效应和多轴应力效应的多轴疲劳寿命模型。 13.5 MPa内压下的旋转弯曲疲劳试验结果在三重误差离散范围内，验证了所提出的寿命模型的准确性。