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首页> 外文期刊>International Journal of Plasticity >A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels
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A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels

机译：用于9-12％Cr钢的高温循环行为的热力学粘弹性粘液模型

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摘要

Improving the understanding of the long term rate dependent behaviour of materials is of critical importance in many engineering applications. Without this understanding, it is potentially difficult to ensure safe and effective plant operation while simultaneously satisfying requirements for sustainability and responsible resource management. In the present work, a thermodynamically-based constitutive model is proposed to capture the rate sensitivity, the stress relaxation and the accelerated cyclic softening observed during cyclic deformation of a P91 steel at an elevated temperature (600 degrees C). The model is developed within the framework of Thermodynamics of Irreversible Processes and Generalized Standard Materials formalism, thereby offering a thermodynamically grounded coupling of both viscoelasticity (semi-recoverable strain accumulation at vastly different time scales) and viscoplasticity (irreversible strain observed above the stress threshold). The later part combines a hyperbolic sine-power flow rule with non-linear isothermal cyclic evolution of isotropic and kinematic hardening. The applicability of the model to various mechanical loadings (e.g., cyclic tensile-compression tests, fatigue relaxation tests, anhysteretic tests) is validated by designing a heuristic optimisation program based on a nonlinear least-squares function coupled with the Levenberg-Marquardt algorithm. The optimisation procedure is informed (through the estimation of initial material parameter estimates and objective function evaluation) by anhysteretic type experiential data only (wherein long term load hold periods are introduced at various points in the waveform). Rate dependency is determined and validated by considering experimental waveforms with different loading (strain) rates (0.1%.s(-1) 0.01%.s(-1) and 0.001%.s(-1)) and ranges (0.25%, 0.4% and 0.5%) to highlight most of the deformation mechanisms involved during the fatigue and relaxation processes. By comparing predict
机译：改善对材料的长期率依赖行为的理解在许多工程应用中具有至关重要的重要性。如果没有这种理解，可能难以确保安全有效的工厂运行，同时满足可持续性和负责任资源管理的要求。在本作工作中，提出了一种基于热力学的本构模型，以捕获速率灵敏度，应力松弛和在升高的温度（600℃）下的P91钢的循环变形期间观察到的加速循环软化。该模型是在不可逆过程和广义标准材料形式主义的热力学框架内开发的，从而提供粘弹性的热力接地偶联（在差异不同的时间尺度的半可恢复应变累积）和粘塑料（在应力阈值上方观察到的不可逆应变） 。后来的部分结合了双曲线正弦流量规则，具有各向同性和运动硬化的非线性等温循环演化。通过设计基于与Levenberg-Marquardt算法耦合的非线性最小二乘函数的启发式优化程序，验证模型对各种机械负载（例如，循环拉伸压缩试验，疲劳松弛试验，干燥测试）的适用性。通过间歇型经验数据（其中长期负载保持周期被引入波形中的各个点），通知优化过程（通过初始材料参数估计和客观函数评估）。通过考虑具有不同负载（菌株）速率的实验波形（0.1％（-1）0.01％。（-1）和0.001％，确定并验证速率依赖性。（-1））和范围（0.25％， 0.4％和0.5％）以突出疲劳和弛豫过程中所涉及的大部分变形机制。通过比较预测

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