基于漏斗试样的C250钢高温扭转低周疲劳行为

Torsional low-cycle fatigue behavior of C250 steel using funnel specimens at elevated temperature

C250钢的扭转疲劳破坏是其主要失效形式之一。为了获得航空材料C250钢的扭转疲劳特性,并消除等直圆棒试样在扭转试验中产生的弊端,依据漏斗试样完成了C250钢在3种高温(150、200、350℃)环境下的扭转低周疲劳试验,获得了在扭转低周疲劳下的扭矩-名义扭转角曲线。基于试验结果,利用FAT方法分析得到了C250钢在3种高温环境下的材料循环本构关系,利用该循环本构关系对漏斗试样进行三维扭转有限元分析,获得漏斗根部剪切应力与扭矩之间的转换公式及漏斗根部剪切应变与名义扭转角之间的转换公式。基于以上试验与分析方法,得到了材料的剪切应变幅-倍循环次数曲线、剪切应力幅-循环分数曲线以及剪切应力-剪切应变的稳定滞回线,发现材料呈现出循环软化特性,并基于Manson-Coffin模型对材料寿命进行了分析。

Torsional fatigue rupture is one of C250 steel＇s main failure forms, in order to obtain torsional fatigue characteris- tics of C250 steel and eliminate the disadvantages of straight rod specimen, a series of torsional fatigue tests on C250 steel at three different elevated temperatures, 150, 200, 350℃ using funnel specimens has been carried out, and the curves of nominal torque-nominal torsional angle for C250 steel at each temperature are given. Based on the test results and finite-ele- ment-analysis aided testing （FAT） method, the effective cyclic constitutive relationships of C250 steel at those temperatures have been obtained. By using these effective cyclic constitutive relationships, 3D finite element analyses of funnel specimen under torsion are used to reveal the transforming relationship between the torque and shear stress at the root of funnel speci- men, as well as the relationship between the nominal torsional angle and shear strain at the root of funnel specimen. On the basis of those test and analyzing methods, the curves of shear stress-times cycles,shear strain amplitude-cyclic fraction and stable hysteresis loop of shear stress-shear strain have been obtained. The material shows cyclic softening by the analysis of the low-cycle fatigue behavior, and the typical Manson-Coffin model is employed to predict the torsional fatigue life of C250 steel at three different elevated temperatures.