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Stress exponent and primary creep parameters using single specimen and strain relaxation and recovery test

机译:使用单个试样的应力指数和主要蠕变参数以及应变松弛和恢复测试

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摘要

Strain relaxation and recovery test (SRRT), requiring one specimen and viscous (permanent) strain, ε_v (≤0.001 per test) on full unloading during primary creep, is presented with results on gas-turbine engine materials: Ti-6246 at 600℃, Discaloy at 500℃, IN-738LC at 850℃ and Waspaloy at 732℃. It is shown that a 'steady-state' in irreversible viscous flow develops during primary creep; the shape of the creep curve is controlled by time-dependent reversible delayed elastic (anelastic) response. The average viscous strain rate during primary-creep, ε_(V(av))(= ε_v/tsr) for load duration, tsR and corresponding ε_v can be used for the determination of the stress exponent, n -v for viscous flow. It is shown that the value of n_v for primary-creep is comparable to the stress exponent, nmin for minimum creep rate. Using a single specimen, SRRTs also allow determinations of Young's modulus, stress exponent, s for delayed-elasticity (anelasticity), about one-third to fourth of n_v, and other parameters for the constitutive equation for primary creep-strictly before creep enhancement due to the onset of microcracking activities. Short-term and long-term SRRT data on Waspaloy indicated that the creep strain at minimum creep rate consists of a significant amount of recoverable strain (32% at 450 MPa and 38% at 650 MPa).
机译:提出了应变松弛和恢复测试(SRRT),该测试需要一个样本和粘性(永久)应变,在一次蠕变过程中完全卸载时需要ε_v(每次测试≤0.001),并在燃气轮机发动机材料上得到了结果:Ti-6246在600℃ ,500摄氏度的Discaloy,850摄氏度的IN-738LC和732摄氏度的Waspaloy。结果表明,在一次蠕变过程中会产生不可逆粘性流的“稳态”。蠕变曲线的形状由时间相关的可逆延迟弹性(非弹性)响应控制。一次蠕变过程中的平均粘性应变率ε_(V(av))(=ε_v/ tsr)对于载荷持续时间tsR和相应的ε_v可用于确定应力指数n-v对于粘性流。结果表明,一次蠕变的n_v值与最小蠕变速率的应力指数nmin相当。通过使用单个样本,SRRTs还可以确定杨氏模量,应力指数,延迟弹性(无弹性)的s,n_v的约三分之一至四分之一,以及其他参数(主要用于蠕变本构),主要用于蠕变增强之前的蠕变。微裂纹活动的开始。 Waspaloy上的短期和长期SRRT数据表明,最小蠕变速率下的蠕变应变包括大量可恢复应变(450 MPa时为32%,650 MPa时为38%)。

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