A Structural Damage Monitoring Method Based On Mobile Sensing System And Its Experimental Research

A distributed sensor network which is permanently integrated into the structures is regarded as a revolutionary method in the field of structural health monitoring (SHM). Currently, such method using piezoelectric transducers (PZT) has been extensively developed to provide detection of flaws in the structure. To achieve this, PZT can generate Lamb wave to locate damage in large-scale structures, and simultaneously apply electro-mechanical impedance for local damage detection. Generally, transducers are often bonded on the surface of the structure. However, such traditional installation method has some obstacles in practical application:such as adhesive interface inhomogeneity, limited service life, and the need for a large number of sensors to monitor large-scale structures which even increase structural weight.To overcome above shortcomings, this study develops the new concept of mobile sensing system which makes use of a mobile transducer set to monitor large-scale structures (especially, a large aircraft structure such as wing, fuselage, and empennage). The mobile transducer set included PZT probes which can be easily moved on the surface of the structure. The PZT probes use dry-coupled for energy transfer to the structure. A hybrid method including the lamb wave based method for global damage location and electro-mechanical impedance based method for local damage quantification, provides a better resolution of damage in a the monitoring area. Around the key issues of the mobile sensing system, this thesis investigates the following issues:(1) Introducing the fundamental of piezoelectric transducers and their application in SHM.(2) The design of a mobile transducer set using vacuum adsorption, and a portable PZT probe for data acquisition.(3) Investigating the efficiency of dry-coupled form for guided wave excitation and receiving by the PZT. Moreover, the effect of boundary conditions and clamping force are also studied in theory. The preliminary experimental results were shown that the proposed mobile sensing system is feasible damage detection in aluminum plates.(4) Analysis of the electro-mechanical impedance of PZT using dry-coupled and the parameters which play a role in electro-mechanical impedance changes. Then some experiments were set up to investigate the efficiency of the developed method in detecting representative damages including through-thickness hole and cracks in plates using the developed portable PZT probe.(5) Investigating the specific process and steps toward the implementation of the mobile structural health monitoring strategy using a hybrid method including lamb wave based method with electro-mechanical impedance based method for damage detection in the structures.This thesis develops a mobile sensing system, which can take the advantage of the flexibility, mobility, extensibility and integrating the lamb wave based method for global and electro-mechanical impedance based method for local and in service damage detection.