Development of Ultrascnic Flaw Detection System for Quantitative Evaluation of Fatigue Damage of Existing Steel Structures

本研究考虑了以下项目，并展示了开发UT系统进行定量评价的可能性。现有钢结构疲劳裂纹检测数据库的开发及基于该数据库的咨询系统：建立了钢结构疲劳损伤的位置、原因和修复工作数据库，说明了缺陷裂纹检测对维修的重要性。超声回波特性的数值模拟：为了研制线阵探伤系统，对压电器件进行了波传播仿真，优化了线阵探伤系统的布置。提出了2 MHz和5 MHz的有效配置方案。3 .疲劳裂纹超声回波特征的验证：通过超声回波强度的变化，可以无损地检测裂纹尖端的开合行为，为疲劳裂纹的可视化识别提供了可能性。阵列超声探伤系统的研制：研制了采用串联或二维阵列探伤探头的钢的三维探伤系统。利用信号处理技术提高超声探伤系统的精度：发展了客观、准确的三维可视化技术。评价了利用SAFT等技术可视化检测裂纹尖端位置的精度。利用钢结构模型进行实验验证：利用最近发现的钢框架桥墩的疲劳问题，验证了焊缝缺陷检测的能力，并验证了即使缺陷具有三维形状，也能准确检测出焊缝内部缺陷。结果表明，超声探伤系统可以较为客观地评价疲劳损伤。

This study considered following items and show the possibility of developing UT system for quantitative evaluation.1. Development of a database for the fatigue crack detection in existing steel structures and consultation system based on the database :The database of the location, cause, and retrofit work of the fatigue damage was developed and it was showed that the importance of the detection of cracks from defect for the maintenance.2. Numerical simulation about characteristic of ultrasonic echo :In order to develop linear array flaw detection system, wave propagation simulation was carried out to optimize the arrangement of piezoelectoric device in proves. Then effective arrangement for 2 MHz and 5 MHz were proposed.3. Verification of the characteristics of ultrasonic echo from fatigue crack :It was showed that crack tip opening and closing behavior could be detected as the change of ultrasonic echo intensity non-destructively, and that possibility of fatigue crack identification by visualization using SAFT technique.4. Development of array ultrasonic flaw detection system :Three dimensional flaw detection systems in steel using tandem or two dimensional array probes were developed.5. Improvement of the accuracy of ultrasonic flaw detection systems by signal processing :Three dimensional visualization techniques with high objectivity and accuracy was developed. Accuracy of visualization to detect the location of crack tip by SAFT technique etc was evaluated.6. Verification by experiment using steel structural models :Ability of the weld defects detection was verified by using the model of steel bridge frame piers, which is fatigue problem was found recently, then it was checked that internal weld defects can be detected accurately even if the defect had three dimensional shapes.From the these results, it can be established that ultrasonic flaw detection system to evaluate fatigue damage objectively.