摘 要: 通过一系列单轴应力循环实验对 T 225NG 钛合金进行了长次循环棘轮行为研究。研究表 明, 在一定峰值应力范围内经数万次应力循环后材料具有棘轮安定性; 棘轮疲劳损伤与幅值应力 和峰值应力相关, 当幅值应力为峰值应力的一半时, 棘轮变形达到安定后产生疲劳破坏, 疲劳寿命 与峰值应力或 SR 应变( 饱和棘轮应变) 之间满足幂律关系; 在幅值应力仅为峰值应力的 1% ~ 25% 时, 材料依然可以产生棘轮塑性应变累积并经过数十万次循环后达到安定, 且蠕变附加效应 不显著; 当峰值应力取为屈服强度 85% ~ 100% 时, 初始棘轮塑性应变率为零, 但经过数万次循环 后仍可以产生 1 4% ~ 2 5% 塑性应变累积。基于峰值应力与 T225NG 合金单轴棘轮塑性累积之 间所具有的单调特性以及棘轮演化的门槛特性, 本文重点发展了 SRM 抛物律本构模型, 该模型可 较好预测 T225NG 合金单轴 SR 应变, 也可用于估算蠕变的安定塑性累积。论文还讨论了关于棘 轮演化的分类问题。
关键词: T225NG; 钛合金; 安定; 棘轮; 循环; 塑性; 应力; 应变; 疲劳; 蠕变
Ratcheting Behavior of T225NG Titanium Alloy under Uniaxial Cyclic Stressing: Experiments and Modeling
Abstract: In order to investigate the ratcheting behavior of T225NG alloy, a series of ratcheting tests under uniaxial long cyclic stressing were performed. The results show that the ratchet ing strain of this alloy can get into shakedown after tens ( or hundreds) of thousand cycles. After the ratcheting strain is saturated under the condition that stress amplitude is half of peak stress, it will bring about subsequent fatigue failure, and relationship between fat igue life and one of peak stress and saturated ratcheting ( SR) strain meets pow er law . As the alloy is under stress jiggling with stress amplitude that is 1% 25% of peak stress, the ratchet ing strain still become remarkable and goes into shakedown after several hundreds of thousand cycles but there exists little accessional strain caused by creep effect. It is notable that, w hen t he peak stress is 85% 100% of yield stress, t he long cyclic stressing will lead SR strain to be from 14% to 2 5% even if the initial ratio of ratcheting strain is zero. Based on ratcheting threshold proper ty of peak stress and monotonicity of relationship between the peak stress and SR strain, a saturated ratcheting model ( SRM ) is developed to predict SR strain and to estimate saturated creep strain also. In addition, t he classes of ratchet ing evolutions of metals are discussed.
Key words: T225NG; t itanium alloy; shakedown; ratcheting; cycle; plasticity; stress; strain; fa tigue; creep