Thermal Sprayed Coating as a Structural Health Monitoring Sensor for Engineering Structures
Creators: Ogunbadejo, Adekunle S.
Publisher: name: University of Alberta Library
Year: 2023

<p>Failure prevention in engineering components is vital to efficiently reducing costs and very crucial to preservation of lives. Crucial to this failure prevention is the requirement of knowing stresses within the components, not just to counter the risk of overloading but also to determine the onset of failure, and thus influence its economic and social consequences. Given the economic importance of failure, more emphasis should be placed on developing more effective and economically viable solution to failure prevention. In this doctoral research program, the main objective was to develop thermally sprayed coatings for use as structural health monitoring (SHM) sensors to monitoring in-service stresses through electromechanical measurements. The components of focus are wind turbine blades and pipes used in oil and gas. Mechanical blend of a nickel alloy (NiCoCrAlTaY) powder and titania (TiO2) powder was used to fabricate flamed-sprayed coatings on steel plates, steel pipes and carbon fiber reinforced composite (CFRP) plates. The choice of the powder mixture was to optimize the piezoresistive response of the coating layer. To prevent electrical short circuiting of the bi-layered coating-substrate system, a flame-sprayed alumina (Al2O3) was deposited on all the substrates before depositing the conductive layer.<br>
In the first stage of the experimental study, the impact of TiO2 on the porosity, electrical resistivity, and gauge factor of NiCoCrAlTaY coating was investigated. Both tensile and cyclic tests were performed to investigate the piezoresistive sensitivity of the conductive layer on steel plates. To investigate the effectiveness of the coating to monitor stresses in pressurize vessel, experimental study was also conducted through internal pressurization with hydraulic oil at different pressures with the coating on steel pipes. Since the current trends in wind turbine blades fabrication is heavily tilted towards utilization of composites, tensile tests were carried out on CFRP coated with the nickel alloy through flame spray technique. The results suggested that the coatings can perform as good surface strain monitoring sensors in steel and CFRP substrates. The gauge factor of the coating, which is a measure of strain sensitivity, reached 4.2 and 146 on CFRP and the steel substrates, respectively.<br>
The second stage of the research involved using analytical modelling techniques to investigate the electromechanical interaction of the conductive layer with an elastic substrate in the bi-layered coating-substrate system. Effective material properties were used for the coating and the substrate was modelled as an elastic half-plane. Subsequently, analytical investigation was done on the effect of imperfect interfaces in the form of delamination and the effects of bending on the piezoresistive response of the coating-substrate system. Through the analytical model of the system, the strain distributions in each layer in the bi-layered coating-substrate system was established. Also, the load transfer mechanism, which plays a significant role in establishing the transfer function between substrate and the conductive layer, revealed that load transfer from the substrate to the conductive layer was mainly through the edges of the insulating layer.</p>