Stress relaxation at high temperatures and the role of delayed elasticity
Stress relaxation at high temperatures and the role of delayed elasticity
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DOI：
10.1016/j.msea.2004.10.003
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发表时间：
2005-02
期刊：
影响因子：
6.4
通讯作者：
N. K. Sinha;Shoma Sinha
中科院分区：
文献类型：
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作者：
N. K. Sinha;Shoma Sinha
不同应变下的恒温闭环控制应力松弛试验(SRT)得出结论：SRT在较宽的应力范围内不能提供预期的粘性应变率；幂定律蠕变的应力指数依赖于应变。SRT后的恢复阶段表明，在应力松弛的初始阶段，无论约束程度如何，控制松弛过程的是延迟弹性，而不是粘性流动。粘性流动只在较长时间内控制应力松弛，表现出接近准稳定应力率的“明显”渐近。SRT的局限性可以通过根据独立的等温恒应力应变松弛和恢复试验(SRRT)得到的三组分流变方程来描述松弛过程来解释。理论上预测了随时间变化的可恢复(延迟弹性)应变分量和永久应变分量随时间和外加应变的变化。以一种钛基α-β，Ti-6Al-2SN-4Zr-6Mo合金为试验材料，在600°C(0.45Tm)温度下进行了实验，结果表明了传统实验和分析方法的不足，并说明了本配方的强度。
Closed-loop controlled isothermal ‘constant-strain’ stress relaxation tests (SRT) at different strains led to the conclusion that SRT cannot provide the anticipated viscous strain rate over a wide stress range; the stress exponent for power-law creep was found to depend on strain. The recovery phase after SRT showed that delayed elasticity, not the viscous flow, controls relaxation processes during the primary stages of stress relaxation irrespective of the level of constraint. Viscous flow controls stress relaxation only at longer times exhibiting ‘apparently’ asymptotic approach to a quasi-stable stress rate. Limitations of SRT can be explained by formulating the relaxation processes on the basis of a three-component rheological equation, derived from independent isothermal constant-stress strain relaxation and recovery tests (SRRT). Theoretical predictions were made for the time-dependent recoverable (delayed elastic) and permanent components of strain as functions of time and imposed strain. Experimental results exhibiting the short-coming of conventional experimental and analytical approaches and the strength of present formulations are illustrated by using a titanium-based, α–β, Ti–6Al–2Sn–4Zr–6Mo alloy at 600°C (0.45Tm) as a test material.