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

本研究考虑以下几个方面，并显示开发UT系统进行定量评估的可能性.在役钢结构疲劳裂纹检测数据库及基于该数据库的咨询系统的开发：开发了疲劳损伤的位置、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，对声波传播进行了仿真，优化了探头中压电器件的布置。提出了2 MHz和5 MHz时的有效布置方案.疲劳裂纹超声回波特征验证：通过超声回波强度的变化，可以无损检测裂纹尖端的张开和闭合行为，验证了SAFT技术可视化识别疲劳裂纹的可能性.阵列式超声波探伤系统的研制：研制了采用串列式或二维阵列探头的三维钢结构探伤系统.通过信号处理提高超声波探伤系统的准确性：开发了具有高客观性和准确性的三维可视化技术。评价了SAFT等可视化技术检测裂纹尖端位置的准确性.钢结构模型试验验证：以近年来发现的疲劳问题钢桥墩为例，验证了超声波探伤方法的检测能力，并验证了即使缺陷为三维形状，也能准确检测出内部焊缝缺陷，从而建立了能够客观评价疲劳损伤的超声波探伤系统。

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.