T225NG合金的高温单轴棘轮行为研究

Ratcheting Behavior of T225NG Alloy under Uniaxial Loading at Elevated Temperatures

在200、300、350、450℃等温度下对T225NG合金进行了单轴棘轮行为试验研究,分析了温度、应力幅值、低峰值应力棘轮历史对T225NG合金棘轮行为的影响.研究表明,在高温下峰值真应力具有对T225NG合金饱和棘轮应变控制的一元特性,饱和棘轮应变与幅值和先前的低峰值应力棘轮历史无关;在相同峰值应力下,温度越高则塑性应变累积越迅速,饱和棘轮应变越大;高温下T225NG合金出现异化的棘轮应变演化关系,现有本构理论难以描述.基于单试样多级加载试验方法,建立了一个用于预测T225NG合金单轴高温饱和棘轮应变的本构模型,该模型对试验数据有较好的相关性,可以较好地描述单轴棘轮应力与饱和棘轮应变之间的关系.

A series of uniaxial ratcheting tests for T225NG alloy were carried out at 200, 300, 350, 450°C respectively. And the effects of temperature, cyclic stress amplitude and ratcheting history of previous lower peak stress on the ratcheting behavior of T225NG alloy were investigated. The results show that stress amplitude and previous lower peak stress has no effects on saturated ratcheting (SR) state, and then peak true stress is unitary control parameter of SR state of T225NG alloy. In addition, under cyclic stressing with same peak stress, the higher the temperature, the quicker the plasticity accumulation and the larger the SR strain. Moreover, there exists abnormal ratcheting strain evolution of the material and the current constitutive theories are hard to describe it. Based on the experimental data of single-specimen under multistep cyclic stressing, a constitutive model was developed to predict the uniaxial SR strain at elevated temperatures. This model has excellent relativity to the experimental data and then has better capacity to describe the relationship between ratcheting stress and SR strain.