低温环境下光纤光栅传感器的抗疲劳设计

The increasing concerns on energy and environment call for modern plant operating under extreme environments. It is thus important to ensure the safety of critical industrial equipment. However, reliable sensors to measure temperature and deformation at cryogenic temperatures have been a long standing challenge. In this research project, fatigue failure mechanisms and fatigue design of fiber Bragg grating (FBG) sensors at cryogenic temperatures will be investigated. Main contents are as follows: (1) The degradation of the optical characteristics of bare FBGs is obtained under strain cycling at cryogenic temperatures. The effect of temperature amplitude on the thermal fatigue life of bare FBGs is demonstrated, as well as the effect of temperature on the mechanical fatigue life. The prediction models are proposed to account for the temperature effect on the thermal and mechanical fatigue life of bare FBGs, respectively. (2) The degradation of the optical characteristics of FBG temperature/strain sensors is also obtained under strain cycling at cryogenic temperatures. The effects of materials, thickness and process parameters of coating, as well as interfacial bonding characteristics between coating and optical fiber, on the thermal fatigue life of FBG temperature sensors are presented. And the effects of materials, structural parameters and process parameters of packaging, as well as interfacial bonding characteristics between coating and optical fiber, on the mechanical fatigue life of FBG strain sensors are demonstrated. The prediction models are proposed to account for the effects of temperature, coating/package characteristics and interfacial bonding characteristics on the fatigue life of FBG temperature/strain sensors, respectively. (3) Mechanisms of fatigue failure and optical degradation of the bare FBGs and FBG sensors are demonstrated based on microscopic analysis. The relationship between the degraded optical characteristics and the stress/strain distribution in damaged fibers is established. The fatigue design method of FBG sensors is therefore proposed to account for the fatigue properties and their effects on the optical properties at cryogenic temperatures. This basic research thus could provide the fundamental theories and concepts for design and manufacturing of long-term reliable and durable FBG sensors at cryogenic temperatures.

面向保障重大机械产品服役安全的需求，针对低温下缺乏可靠传感装置的问题，开展低温下光纤光栅传感器疲劳失效机理及抗疲劳设计的研究。包括：（1）研究裸FBG在低温-循环应变共同作用下光学特征量退化规律，揭示循环温度幅对热疲劳寿命以及温度对机械疲劳寿命的影响规律，建立考虑温度效应的疲劳寿命模型；（2）研究FBG温度/应变传感器在低温-循环应变共同作用下光学特征量退化规律，厘清低温下涂层/封装的材料/结构/工艺参数及界面结合性能对疲劳寿命的影响规律，建立包含温度效应、涂层/封装效应及界面效应的疲劳寿命模型；（3）基于微观分析，揭示裸FBG和FBG传感器的疲劳失效机理及光学性能退化机制，建立光学性能退化特征量与含疲劳损伤光栅内非均匀应力/应变分布的映射关系，提出考虑低温下疲劳性能及其对光学性能影响的耐低温光纤光栅传感器抗疲劳设计方法。本研究将为高可靠长寿命耐低温光纤光栅传感器的设计制造提供基础理论支撑。

面向保障深冷环境下重大装置服役安全的迫切需要，针对缺乏低温下精确、可靠温度/变形传感装置的问题，本项目致力于低温下光纤布拉格光栅（FBG）传感器的温度/应变响应特性及可靠性、热/机械疲劳行为以及抗疲劳设计的研究，较好地完成了项目的预期计划。主要研究工作及成果包括：（1）改进设计了低温下光纤动态拉伸试验系统，厘清了低温下裸FBG的温度/应变灵敏度随温度的变化规律与机理，分析评估了低温下裸FBG的重复性和稳定性，验证了裸FBG作为耐低温传感器敏感元件的可行性；（2）基于磁控溅射和电镀工艺，发展了耐低温FBG温度/应变传感器的制造工艺方法，研制了新型耐低温金属涂覆FBG温度传感器和金属封装FBG应变传感器，揭示了金属涂覆/封装工艺对FBG传感器光谱特性与传感特性的影响规律及机理，分析评估了低温下FBG传感器的重复性和稳定性，验证了金属涂覆/封装的工艺可行性；（3）改进了低温下金属封装FBG应变传感器机械疲劳寿命试验方法，澄清了低温–常温循环温度幅下金属涂覆FBG温度传感器的光谱特性与传感特性演变特征及失效机理，揭示了低温–循环机械载荷下金属封装FBG应变传感器的光谱特性与传感特性演变规律及失效机制，建立了低温下金属封装FBG应变传感器机械疲劳寿命预测线性方程，探讨了提高低温下FBG传感器疲劳寿命的材料选择、结构设计与工艺优化，初步形成了耐低温金属封装FBG传感器的抗疲劳设计方法；（4）改进设计了金属涂层光纤单纤维压出试验方法，澄清了涂层材料和电镀工艺对金属涂层/光纤界面结合强度的影响规律及机制，揭示了微纳尺度下光纤表面金属涂层硬度和弹性模量的演变规律与机制，形成了较为系统的金属封装光纤传感器制造工艺方法。.研究成果为高可靠长寿命耐低温FBG传感器的设计制造提供了一定的理论基础与方法。项目执行期间共发表学术论文6篇，其中SCI/EI检索论文5篇，授权美国专利1项、中国发明专利1项、实用新型1项，申请中国发明专利1项。项目负责人荣获上海市科技进步一等奖1项，国际学术会议最佳论文奖1项。培养博士研究生1名、硕士研究生2名。