损伤对航空发动机锯齿形尾喷管力学性能的影响

 锯齿形尾喷管，是一种位于发动机喷口处由环形分布的锯齿组成的航空动力学装置，用于降低发动机噪声。锯齿形尾喷管在使用过程中反复变形，必然会出现结构性损伤问题。在已有形状记忆合金本构模型和碳纤维复合材料疲劳试验的基础上，引入损伤因子，利用有限元仿真研究了形状记忆合金和碳纤维复合材料疲劳损伤对锯齿形尾喷管力学性能的影响。结果表明，锯齿形尾喷管的结构损伤主要由形状记忆合金决定，随着循环次数的增加，锯齿形尾喷管上所受最大等效应力逐渐减小，最大位移逐渐增加。相较于尾喷管单齿的损伤结果，在相同损伤因子下锯齿形尾喷管所受最大等效应力大于单齿损伤时所受最大等效应力，锯齿形尾喷管的最大位移均小于单齿损伤时的尖端最大位移。

The effects of damage on mechanical behavior of jet engine variable geometry chevron

The variable geometry chevron(VGC) is a sawtooth aerodynamic device composed of an annularly distributed single chevron at the tail of the engine, and is used to reduce the engine noise. The VGC is deformed repeatedly during takeoff and landing of the aircraft, which would cause the structural fatigue of the VGC. Based on the existing constitutive model of the Shape Memory Alloy(SMA) and the fatigue test of the Carbon Fiber Reinforced Plastics(CFRP), a damage factor is introduced in a finite element subroutine to analyze the mechanical properties of the VGC when the SMA and the CFRP are damaged in a certain degree. It is shown that the damage of the VGC is mainly caused by the SMA. As the number of the deformation cycles increases, the maximum Mises stress in the VGC gradually decreases and the maximum displacement gradually increases. Compared with the simulation of a single chevron, the maximum Mises stress of the VGC with the same damage degree is larger, and the maximum displacement of the VGC is smaller than the tip deflection of the single chevron. The research results can provide a guidance for the safe operation of the VGC.