N18合金薄壁管高温应变循环与疲劳行为研究

应用新型自研夹具对N18合金薄壁短管进行400℃下的单轴拉伸和等幅低周应变疲劳试验。试验结果表明：N18短管高温循环应力应变滞回线有良好对称性；等幅循环下短管试样在较低应变幅下表现出循环硬化特性，而在较高应变幅下表现出循环软化；在多级应变循环加载下短管试样应力幅在循环中均保持稳定，循环本构关系不受多级应变循环工况差异的影响；材料循环特性不符合Manson律。获得了用于N18合金在400℃高温下的几个寿命估算式。

Study on Cyclic Behaviour and Strain Fatigue of N18 Alloy Thin-Walled Tubes at Elevated Temperature

Based a pair of self invented clamps, a series of strain fatigue tests at 400 ℃ based on thin walled tubular specimens of N18 alloy were carried out. The results show that cyclic strain stress curves are symmetrical due to the clamps, and the alloy behaves cyclic hardening at lower strain amplitude and behaves cyclic softening at higher strain amplitude under cyclic straining, therefore N18 alloy does not follow Manson law, however, under multigrade strain cycling (MSC) with different loading ways, stress amplitude response of the alloy remains stable or cyclic constitutive relationships of the alloy tubes are closed each other. Finally, several life estimated equations for the alloy tubes were presented.