Development of non-destructive detection system of breathing cracks using dynamic response

在这个项目中，首先，我们开发了一种具有呼吸裂纹的梁的振动分析方法。该方法采用基于混合变分原理的有限元法建立控制方程。然后，采用增量谐波平衡法求解控制方程。结果表明，该方法能较好地分析含呼吸裂纹梁的稳态振动，具有较高的精度和效率。在此基础上，提出了一种基于动态响应的梁呼吸裂纹检测方法。通过数值模拟验证了所开发的检测技术能够准确地检测出呼吸裂纹。接下来，为了进一步验证所开发的检测技术的适用性，我们进行了实验。在实验中，我们使用了带有呼吸裂纹的钢梁。模拟呼吸裂纹的方法是在薄锯片上插入与锯片宽度相同厚度的薄钢板。我们用实验的测量数据来检测裂缝。检测结果准确。从而证实了所开发的探测技术对束流的适用性。最后，将梁的检测技术推广到以管道系统为典型的框架结构的检测技术。所提出的基于混合变分原理的分析方法具有无需进行大的修改即可适用于此类框架结构的特点。因此，框架结构的检测过程与梁的检测过程非常相似。数值模拟验证了扩展检测技术的适用性。

In this project, first, we developed a method for vibration analysis of a beam with breathing cracks. In the developed method, the governing equations are formulated using the finite element method based on the mixed variational principle. Then, the governing equation is solved using the incremental harmonic balance method. We confirmed that the developed method can analyze steady-state vibrations of a beam with breathing cracks with high accuracy and efficiency. Next, we developed a detection technique of breathing cracks in a beam using dynamic response based on the developed analysis method. We confirmed via numerical simulation that the developed detection technique can detect breathing cracks accurately. Next, in order to check further the applicability of the developed detection technique, we conducted experiment. In the experiment we used a steel beam with a breathing crack. The breathing crack was simulated by a thin saw-cut to which the thin steel plate with the same thickness as the width of the saw-cut was inserted. We used measured data from the experiment to detect the crack. The accurate detection result was observed. Thus we confirmed the applicability of the developed detection technique for a beam. Finally, we extended the detection technique for a beam to a technique for a frame structure whose typical is a piping system. The developed analysis method based on the mixed variational principle has feature that it can be applied to such a frame structure without large modification. Thus the procedure of the detection technique for a frame structure is very similar to that for a beam. The applicability of the extended detection technique was confirmed by numerical simulation.