基于应变梯度的结构损伤监测理论与技术研究

In-situ monitoring of the damages status in complex aerospace structures is very important for the safe service of the aircraft. The onset of damage cracks commonly occurs at the areas with high stress concentration, such as mechanical joints, and the interfaces between composite laminas. Effective detection of these early-stage cracks could prohibit the structures from systematic failures, however, such approach for the in-situ monitoring of defects status is currently unavailable. This project will use flexoelectric strain gradient sensing technology to theoretically and experimentally investigate the approaches for monitoring the early-stage cracks status in mechanical structures. The detailed content includes: build the theoretical model for characterizing the three dimensional strain gradient transfer mechanism between the mechanical structure and the bonded strain gradient sensor (SGS); based on the flexoelectric constitutive equation, construct the electro-mechanical coupling relationship between the SGS responses with the cracks; manufacture the flexible SGS patches with micro-nano flexoelectric structures which are supposed to exhibit enhanced sensing properties; experimentally evaluate the capability of SGSs for in-situ monitoring the early-stage cracks. This project aims at revealing the strain gradient transfer mechanism which will be applied for the structural health monitoring technologies, developing the flexible SGSs patches and establishing the theoretical and technological basis for in-situ monitoring the initiation and growth of cracks in the early stage.

复杂飞行器结构内的损伤在线监测对于飞行器的安全服役具有重要意义。结构中的损伤往往萌发于诸如机构接头、复合材料层间界面等具有高应变梯度的应力集中区域。对这些初期小尺寸损伤的有效检测能够及时避免结构的整体性失效，但目前尚缺少能够实时监测的技术手段。本项目以结构中的初期损伤为研究对象，通过挠曲电应变梯度传感器技术，对损伤监测的理论方法进行研究。具体内容包括：建立粘贴式柔性应变梯度传感器普适结构中应变梯度的三维传递理论模型；基于挠曲电结构的本构模型建立应变梯度传感器与结构损伤的力电耦合关系模型；基于具有增强挠曲电效应的微纳结构制作柔性贴片式应变梯度传感器；通过损伤监测试验验证所获得的应变梯度传递模型，验证应变梯度传感器对结构初期损伤的监测效果。本项目旨在揭示用于结构损伤实时监测的应变梯度传递机制，开发出柔性贴片式应变梯度传感器原理样机，为复杂结构中的初期损伤实时监测奠定理论和技术基础。

机械结构件的损伤在线监测对于装备的安全服役具有重要意义。损伤在萌发初期由于尺寸较小，目前尚缺少能够实时监测的技术手段。本项目主要开展挠曲电效应传感器的应变梯度传感机理，试图为早期损伤监测提供一种新的技术手段。研究成果包括：建立了粘贴式柔性应变梯度传感器普适结构中应变梯度的三维传递理论模型；基于挠曲电结构的本构模型，建立了应变梯度传感器与结构损伤的力电耦合关系模型；揭示了内部缺陷对材料挠曲电性能的影响机理，提出了增强挠曲电材料的设计方法；建立了挠曲电结构在大应变梯度下的非线性理论模型。