长时保载情况下奥氏体不锈钢的蠕变-疲劳失效机理及本构模型研究

The austenitic stainless steel has been widely used in the high temperature pressure vessel and piping system in the Power plant due to its excellent high temperature endurance, corrosion and oxidation resistance. During the service period, the above-mentioned high temperature equipment often experiences creep-fatigue damage with long-term holding characteristics. In this project, the austenitic stainless steel used in the high temperature pressure vessels will be chose for the following studies: (1) A reasonable creep-fatigue test method with long term holding and creep damage dominant feature will be designed for the systematic macro and micro experimental study, and the creep-fatigue deformation evolution rule, interaction feature and failure mechanism in the creep damage dominant area of the austenitic stainless steel will be investigated. (2) Based on the analysis of various micro and microscopic failure mechanisms in the creep- fatigue process, a damage equation concerning the creep-fatigue interaction in the creep dominant area will be established. (3) The damage coupled whole life constitutive model will be established and the corresponding finite element planting will be carried out to verify the accuracy and rationality of the constitutive model. The findings will enhance the knowledge level of the solid mechanics on the aspect of creep-fatigue interaction significantly. Furthermore, the related achievements will also give important theoretical supports for the safety assessment and life prediction of the advanced high temperature components.

奥氏体不锈钢由于优异的高温持久强度和抗腐蚀、氧化性能，被广泛应用于电站高温压力容器和管道系统中，这些高温设备在服役过程中往往伴有具有长时保载特征的蠕变-疲劳损伤。针对这一关键问题，本项目将以核电压力容器用奥氏体不锈钢为研究对象，开展如下研究：（1）设计合理的蠕变-疲劳实验方法，开展长时保载情况下、蠕变主导的蠕变-疲劳交互作用宏、微实验研究，揭示该材料在蠕变主导区的蠕变-疲劳变形规律、交互作用特征和失效机理；（2）基于蠕变-疲劳过程中多种微、细观失效机制的演化规律，建立具有明确物理意义， 反映蠕变-疲劳交互作用的损伤方程；（3）建立能够合理描述蠕变主导区内奥氏体不锈钢蠕变-疲劳行为的、耦合损伤的全寿命本构模型，并对其进行有限元移植，验证本构模型的准确性和合理性。研究成果将会有力提高固体力学在蠕变-疲劳方面的认识水平，为相关高温构件的安全评估和寿命预测提供理论支持。

在核电火电、航空航天等高端装备中，热端部件受其服役情况的影响，将面临严重的蠕变-疲劳交互作用和失效风险。基于以上背景，本项目以GH4169镍基高温合金为研究对象，通过对实验设备的二次开发，建立了应力、应变混合控制的蠕变-疲劳实验方法，实现了对蠕变损伤和疲劳损伤比例的合理控制，开展了疲劳损伤主导、蠕变-疲劳交互和长时保载情蠕变主导的蠕变-疲劳宏、微实验研究，揭示了该材料蠕变占比区内的循环变形规律、交互作用特征和失效机理；同时，基于蠕变-疲劳过程中多种微、细观失效机制的演化规律，建立具有明确物理意义，反映蠕变-疲劳交互作用的损伤方程，并基于有限元平台对其进行了数值实现；建立了可以合理描述GH4169镍基高温合金在蠕变-疲劳载荷下的循环变形行为的、耦合损伤的全寿命本构模型，并对其进行有限元移植，验证本构模型的准确性和合理性，实现了对缺口试样的合理寿命预测。研究成果将会有力提高固体力学在蠕变-疲劳方面的认识水平，为相关高温构件的安全评估和寿命预测提供理论支持。