Development of Crack Detection System on Structural Members

该研究项目于1997年4月至1999年3月在日本文部科学省(C-2科学研究补助金)的资助下进行。正如今天很容易看到的那样，结构系统的规模和复杂性往往会增加，保证或改善安全的措施自然变得至关重要。作为对新的安全要求的回应，现在对结构构件的应力水平进行检查、连续监测和记录的情况并不少见。现在的一个重要概念是对结构进行“健康监测”，因为一旦出现缺陷和结构异常，就会及时发现它们。这项工作的目标是多方面的。本研究首先对疲劳裂纹扩展的断裂力学模型进行了综述。将分析监测任何现有裂缝和收集相关数据的系统。基于概率可靠性…方法的裂纹扩展参数估计更多的质量工程也将被考虑。对利用光纤和激光传感器检测裂纹和测量应变变形的新方法进行了可行性研究，主要结果和进展是：1)通过与经典欧姆应变计的比较，证实了基于光纤传输激光的光学应变计的有效性；2)注意到当运动方向(压缩或拉伸)发生变化时，通过分析光干涉图样来测量应变是困难的。3)对激光传感器和光纤监测疲劳裂纹扩展的有效性进行了测试。还得出了其他结论，但报告中没有提到传播参数的估计问题。在这项研究的继续中，将继续澄清利用光学传感器确定裂纹扩展起点的问题。此外，作为补充，这项工作是按照最初的研究计划进行的，并于1999年3月结束。较少

This research project was conducted from April 1997 to March 1999 with financial support from the Japanese Ministry of Education, Science & Culture (Grant-in-Aid for Scientific Research C-2). As can be readily seen nowadays, structural systems tend to increase in size and complexity, and naturally measures to guarantee or improve safety became essential. As a response to the new safety requirements, inspection, continuous monitoring and recording of the stress levels in structural members are not uncommon now. An important concept now is of that of "health monitoring"of structures in that defects and structural anomalies are timely detected as soon as they emerge. The objectives of this work were multi-faceted. The research started by a survey of the fracture mechanics models for fatigue crack propagation. Systems for monitoring any existing cracks and collecting pertinent data were to be analyzed. The estimation of crack propagation parameters based on methods of probabilistic reliabi … More lity engineering was also to be considered. A feasibility study of a new method using optic fibers and laser sensors for detection of cracks and measurement of strain deformation was to be conducted.The main results and developments of the work are : 1) The efficacy of optical strain gages, based on the propagation of laser through optical fibers, developed specially for this research, was confirmed after comparisons with the classical ohmic strain gages ; 2) It was noticed that the determination of strains, which is done by analyzing light interference patterns, is difficult when the direction of movement (compression or tension) changes. It is now inquired if separating the laser light into a signal part and a reference one would not solve the problem ; 3) Testing for the assessment of the validity of the monitoring of propagation of fatigue cracks by laser sensors and optical fibers was conducted. Other conclusions were also drawn, but the problem of estimation of propagation parameters ins not mentioned in the report. In the continuation of this research, the clarification of the problem of determining the start point of crack propagation by using optical sensors is to be pursued.Also, as an additional remark, this work as conducted accordingly to the initial research plan, and was concluded on March 1999. Less