Vibration-based Techniques For Beam-type Structures Using Non-destructive Damage Detection

The structural damage detection technique has been one of the most importantresearch topics on the field of Aeronautics and Astronautics. Recently, a significantincrement of interest has been observed for the vibration-based damage detectionmethod. The main advantages of the vibration-based method lie in its non-destructive,simplicity, efficiency and real-time monitoring. The fundamental idea forvibration-based damage detection is that the damage-induced changes in the physicalproperties (mass, damping, and stiffness) will cause detectable changes in modalproperties (natural frequencies, modal damping, and mode shapes). Therefore, it isintuitive that damage can be identified by analyzing the changes in vibration features ofthe structure, furthermore, damage position and quantity can be identified as well.First, this thesis presents the state-of-the-art of damage detection and itsdevelopment trends of domestic and abroad, with special emphasis on the structuralvibration-based damage detection methods. The vibration-based damage detectionmethods are classified into the following major categories: natural frequency-basedmethod, mode shape-based method, curvature mode shaped-based method, strainmode-based method, the mode shape high-order derivative-based method, operatingdeflection shape-based method and flexibility-based method, and their merits anddrawbacks are discussed in detail.Second, on basis of currently available research, with the requirements of structuraldamage detection in non-destructive, convenient and low-cost aspects, the crack isassumed to dimensionless equivalent spring, and cantilever single and multiple crackscan be identified in different injury location and degree of injury. Damage identificationwas performed based on different vibration-based method and the effectiveness of thedifferent methods are compared and discussed in detail. Then the numerical results areverified with experiment on the cantilevers with one and two cracks. The numerical andexperimental results show that the vibration-based damage detection methods cansuccessfully identify the crack damage with small number of measurement points and asmall amount of calculation effect.Final, this thesis focus on structural damage detection based on curvature operatingshapes, which is directly measured by PVDF sensors. The curvature operating shapes and damage index are direct determined from the frequency response functions of thedamaged structures by using PVDF film as sensors. The numerical calculation and theexperimental woks for one and two-cracked aluminum beam were performed to verifythe proposed method. Furthermore, the proposed method was used to investigate thedamage detection of a fuselage skin crack. The theoretical and experimental resultsshow that: this method based on PVDF sensor to measure curvature has good indicatorsof the effectiveness. Comparison to the curvature mode shaped-based method, thismethod does not require numerical difference, avoid the modal analysis process, has agreat ability in filtering noise and high accuracy. It has shown that curvature operatingdeflection method using PVDF sensors has wide prospects for engineering applications.