| In recent years, the nouns of impacts and stress waves appeared constantly in various engineering fields and even our daily lives. The characteristic of material under the effect of impact loads is different from that under the effect of static loads. Therefore, it is necessary to adopt stress wave theory to analyze. With the development and improvement of dynamics, stress waves have been widely used in various fields, such as explosion, seismology, material science, etc. It is a new method to detect the location of defect based on stress wave theory, which is proposed in recent years, especially the detection of defect in pipeline. The pipeline which plays an important role in the transportation has been widely used, with its long-distance transmission, no energy consumption and sustainable use. If the pipeline leakage occurs, both the economics and the health of residents will be destroyed. Therefore, it is necessary to detect the wave stress and the defects in the pipeline.How to choose the sensors with high precision, little weight and free from electromagnetic interference to detect stress waves has been a quite practical problem that we should solve urgently. As passive optical components, fiber Bragg grating sensors have many advantages such as high precision and sensitivity, small volume, insensitivity to electro magnetic disturbance, networked sensing and distant transmission, which are widely used in various engineering fields.The innovation point and main contents of this paper are as follows:1. Combining with the theories of elastic stress waves and fiber Bragg grating sensing, the stress wave created in the elastic bar is detected using fiber Bragg grating testing system, both the location of defect in pipeline is measured.2. The development of stress wave detection methods in one-dimensional elastic rod and the detection of defect in pipeline based on stress wave theory were outlined. The sensing properties, application status and demodulation methods of fiber Bragg grating sensors were introduced.3. Establishing the model of coaxial impact with two elastic bars, the stress wave propagation was simulated and analyzed, then the propagation regulation of stress wave was obtained. Through the simulation analysis of stress wave generated in pipeline, the method of determining L(0,1) guided wave mode was found.4. The stress waves created in elastic rods were detected using both fiber Bragg grating and strain gauges detecting systems. The signals were analyzed in time domain and frequency domain, respectively. When a point of the pipeline was impacted, the L(0,1) guided wave mode generated in pipeline was detected using fiber Bragg detecting system, which can be used to measure the location of defects in pipeline. The energy spectrum was analyzed based on wavelet technology.The results of two systems were comparative analyzed, and the feasibility of stress wave detection and guided wave detection using fiber Bragg grating was experimental verified. This study provides a new method for the detection of stress waves. |
