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

在这个项目中，首先，我们开发了一种方法，用于振动分析的梁呼吸裂纹。在所开发的方法中，控制方程采用基于混合变分原理的有限元法。然后，采用增量谐波平衡法求解控制方程。我们证实，所开发的方法可以分析具有呼吸裂纹的梁的稳态振动，具有高精度和高效率。接下来，我们开发了一种检测技术的呼吸裂纹梁使用动态响应的基础上开发的分析方法。我们通过数值模拟证实，所开发的检测技术可以准确地检测呼吸裂纹。接下来，为了进一步检查开发的检测技术的适用性，我们进行了实验。在实验中，我们使用了一个有呼吸裂缝的钢梁。通过插入厚度与锯切宽度相同的薄钢板的薄锯切来模拟呼吸裂纹。我们使用实验中的测量数据来检测裂纹。观察到准确的检测结果。因此，我们证实了光束的检测技术的适用性。最后，我们将梁的检测技术扩展到以管道系统为典型的框架结构的检测技术。本文提出的基于混合变分原理的分析方法具有不需作大的修改即可适用于此类框架结构的特点。因此，用于帧结构的检测技术的过程非常类似于用于梁的检测技术的过程。通过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.