Development of a Global NDT Technique by Infrared Thermography for Strategic Maintenance System of Aging Structures.

近年来，基础设施在设计寿命前老化和劣化已成为一个严重的问题。强调了对老化结构进行适当维护的重要性。传统的基于时间的维修系统在效率、成本、节能等方面存在诸多问题，因此需要引入一种基于服役适应度评价的基于状态的维修系统。本项目开发了一种基于红外热成像测温的新型无损检测技术，用于老化基础设施的结构完整性评估。基于红外热像仪、主动加热设备和时序红外数据处理系统，构建了全局诊断系统。对于混凝土结构，基于傅里叶分析和阶跃加热下瞬态温度分布的锁定分析的热成像无损检测技术被开发用于分层缺陷的识别。对该方法在混凝土试样缺陷识别中的分辨率和适用性进行了实验研究。发现缺陷参数可以定量地由傅里叶系数或相位值确定。针对钢结构疲劳裂纹，提出了一种新的无损检测技术。提出了一种自参考锁定红外热像仪，利用相同的热弹性温度变化序列数据构建参考信号。感兴趣区域的温度变化与遥远区域的温度变化相关，以用于参考信号的构建。随机加载采用基于最小二乘法的锁定算法。将该方法应用于疲劳裂纹识别，检测裂纹尖端附近奇异应力场引起的显著热弹性温度变化。在自参考锁定热图像中，裂纹尖端的对比度变化显著，证明了该技术的可行性。少

In recent years aging and deterioration of infra-structures before their design life has become a serious problem. The importance of appropriate maintenance for aging structures is emphasized. Introduction of a new condition based maintenance system based on the evaluation of fitness for service is required, since the conventional time-based maintenance system has a lot of problems in efficiency, cost, saveenergy, etc. The present project developed a new nondestructive testing (NDT) technique based on the infrared thermographic temperature measurement for structural integrity assessment of aging infra-structures. Global diagnosis system was constructed based on infrared thermography, active heating equipment and processing system of sequential infrared data. For concrete structures, thermographic NDT techniques based on the Fourier analyses and the lock-in analyses of the transient temperature distribution under step heating were developed for the identification of delamination defects … More . Experimental investigations were made on the resolution and the applicability in the identification of defects in concrete samples. It was found that defect parameters were quantitatively determined from Fourier coefficients or phase values. For steel structures, a new NDT technique was developed for detecting and sizing of fatigue cracks. A self-reference lock-in infrared thermography was developed, in which a reference signal was constructed by using the same sequential data on thermoelastic temperature change. Temperature change in a region of interest was correlated with that in a remote area for reference signal construction. The lock-in algorithm based on the least squares method was employed for random loading. Proposed technique was applied for fatigue crack identification based on the detection of significant thermoelastic temperature change due to the singular stress field in the vicinity of crack tips. It was found that significant contrast change was observed at the crack tip in the self-reference lock-in thermal image, demonstrating the feasibility of the proposed technique. Less