Development of Crack Detection System on Structural Members

点击翻译按钮获取中文摘要

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