Stress Wave Detection Technology Of Sheet Based On Fiber Bragg Grating

With the development of industry, the sheet material is widely used in engineering structure, aerospace, shipbuilding, and building decoration in recent years. As a part of the large machinery, the sheet material is damaged frequently due to the impact of the collision force or long-term using which causes material aging. Therefore, it is necessary to conduct a high quality detection to the sheet structure to meet the project requirements, while avoids the property loss and even casualties. Since the traditional electromagnetic sensing technology failed to meet the requirements of high-precision, as a kind of a new sensor, the fiber grating has many advantages which the electromagnetic sensor cannot match, such as the light weight, the small volume, the high precision and anti-electromagnetic interference, suitable for harsh environments. It is widely applied in engineering.When it encounters cracks, lamination and other defects, the stress wave signal reflected and scattered which carries lots of information. The capability of the sheet will be excellently identified which provides a reference for the structural optimization by detecting and analyzing the signal.In this paper, the stress wave in the plate is analyzed based on ANSYS/LS-DYNA and measured by the experiment. The main works of this paper include the following aspects.1. The stress wave types and the ultrasonic wave in the sheet are elaborated. The development, the application and demodulation methods of the fiber grating are briefly described, while the research status of the stress wave detection in the sheet are comprehensively introduced.2. The working principle and sensing properties of the fiber grating are analyzed systematically. The stress wave theories in the unlimited and limited sheet are introduced, and then the reflection and transmission of the stress wave meeting different mediums are discussed. In the end, the plastic stress wave in the sheet is briefly analyzed.3. The model of the sheet and the impact rod which are dynamically simulated and analyzed are built based on the ANSYS, and then the stress distribution is obtained. The strain time covers are obtained correspondingly given the different rod sizes, the impact velocity, the material properties and thicknesses of the plate. The measuring points in the plate are determined according to the simulation results.4. The percussion device is built and the stress wave in the plate is detected using FBG. The stress wave is monitored with the different parameters. It is shown that the experiment results are consistent with the simulation results very well. The detection of a crack in the aluminum alloy plate with the ultrasonic-FBG sensing technique is introduced finally, and the location of the crack can be determined according to the oscilloscope information.