Papers by Keyword: Structural Health Monitoring (SHM)

Abstract: The structural integrity of a composite structure can be greatly compromised by damage inside the component. Invisible damage, e.g. caused by low-speed impact, can significantly reduces composite components capability to efficiently carry loads. In the present study, an innovative approach of strain-based delamination identification and localization is investigated, based on the efficient processing of full-field surface strain measurements. Surface strain data, potentially derived by full-field optical methodologies are used in the assessment of the delamination pattern, through strain field perturbations caused due to damage evolution. Relations between delamination damage and surface strain field disturbances are established by exploiting data decomposition methods using Zernike polynomial moments. The methodology is successfully demonstrated in the case of a stiffened composite panel.

Abstract: One method that has shown great potential in visualising and characterising the interaction of guided waves with damage in composites is Laser Vibrometry. A Laser Doppler Vibrometer (LDV) can be used to produce 2D wavefield images of guided Lamb waves but a single scan is very time consuming and normally multiple scans are required at various frequencies in order to determine the best input signal. This paper demonstrates the use of a chirp excitation method requiring only a single scan and a post-processing algorithm to obtain results corresponding to any narrowband signal within the frequency range of the chirp signal. The method was used on an artificially delaminated composite panel and showed that the S₀ mode, dominant at higher frequencies, mainly caused mode conversions whilst the A₀ mode, dominant at lower frequencies, mainly caused a change in phase and amplitude across the delaminationOne method that has shown great potential in visualising and characterising the interaction of guided waves with damage in composites is Laser Vibrometry. A Laser Doppler Vibrometer (LDV) can be used to produce 2D wavefield images of guided Lamb waves but a single scan is very time consuming and normally multiple scans are required at various frequencies in order to determine the best input signal. This paper demonstrates the use of a chirp excitation method requiring only a single scan and a post-processing algorithm to obtain results corresponding to any narrowband signal within the frequency range of the chirp signal. The method was used on an artificially delaminated composite panel and showed that the S₀ mode, dominant at higher frequencies, mainly caused mode conversions whilst the A₀ mode, dominant at lower frequencies, mainly caused a change in phase and amplitude across the delamination.

Abstract: In this paper, the application of the dual boundary element method (DBEM) in the field of structural health monitoring (SHM) is explored. The model involves a 3D host structure, which is formulated by the DBEM in the Laplace domain, and 3D piezoelectric transducers, whose finite element model is derived from the electro-mechanical behaviour of piezoelectricity. The piezoelectric transducers and the host structure are coupled together via BEM variables. The practicability of this method in active sensing applications is demonstrated through comparisons with established FEM and parametric studies.

Abstract: Bonded repair of composite structures still remains a major concern for the airworthiness authorities because of the uncertainty about the repair quality. This work, investigates the applicability of conventional Structural Health Monitoring (SHM) techniques for monitoring of bonded repair with ring-shaped low profile sensors. A repaired composite panel has been sensorized with two Ring-Shaped Polyvinylidene fluoride piezopolymer Sensors (RSPS) and a piezoelectric (PZT) transducer. An electromechanical impedance (EMI) and Lamb wave analysis have been carried out to check the sensitivity of these sensors to detect an artificially introduced damage simulating a disbond of the repair. The state of the repair have been successfully monitored and reported by both methods.

Abstract: Monitoring of structural integrity of a component is very important, especially for the damage sensitive laminated composite structures. Among the Structural Health Monitoring (SHM) techniques, the Acousto-Ultrasonic (AU) technology is very promising. However, the accurate simulation of Lamb wave propagation is a very demanding task, in terms of computational cost. In the present study, in the frame of Finite Element method, the stacked-shell methodology is proposed for the simulation of Lamb wave propagation in composite laminated panels. The results of the stacked-shell approach are initially evaluated with respect to experimental results; the method is subsequently applied to undamaged and damaged composite laminated panels, in order to assess its efficiency and accuracy in the simulation of Lamb wave-based damage detection techniques.

Abstract: The Port Bridge across Danube in Bratislava is about 461 m long with 4 spans. The bridge was designed for both a highway and simultaneously for two railway tracks. Nowadays the construction is overloaded and that is why the structural health monitoring of the bridge is being developed. The test setup consists of two measuring polygons. This setup needed an original LabVIEW program, which has been developed in cooperation with experts – electrical engineers and experts on structural mechanics. Main problem was to achieve a synchronization of both measuring polygons connected by Wi-Fi antennas. Except of software difficulties there were complications during in-situ measurement, like cable connection between highway and railway level and especially the time synchronization of the traffic video and measurement. The measurement has been done and some eigenmodes have been identified from ambient data.

Abstract: In this present work, the experimental study of developing the smart material by using 2 different preparation methods for developing nanomaterial for Glass fiber reinforced polymers (GFRP) in order to determine the structural damage. The first method deals with the development of Fiber mat using PVA-CNF (Poly vinyl Alcohol-Carbon nanoFiber) and PVA-CNT (Poly vinyl Alcohol – Carbon nanoTube) , which is embedded into the GFRP. Second method deals with the dispersion of both CNF and MWCNT with epoxy matrix (sonication process) to manufacture GFRP by using Vacuum Resin Transfer Molding (VARTM) process. Embedding CNT and CNF fiber is easy which does not downgrade the material’s mechanical properties. PVA-CNF and PVA-CNT sensors were placed at various orientations and different wt. % of CNT and CNF fiber mat were manufacture and embedded on the GFRP has been done in first method, and in the second method, dispersion of the CNF-MWCNT with various wt. % in the GFRP composite has been done. The various incremental loading-unloading step had been applied to the manufactured specimens and their corresponding electrical resistance were observed. The electrical conductivity of the fiber sensor and nanomatrix were compared, due to its resistivity effect on the specimens will be monitored and simultaneously the potential for stress/strain and damage monitoring during the mechanical tests can be assessed.

Abstract: Impedance-based structural health monitoring (SHM) techniques have been developed as a promising tool for real-time structural damage assessment, and are considered as a new non-destructive evaluation method. It is gaining popularity due to its potential of reducing maintenance costs while increasing safety and reliability. This article present the results of Finite Element analysis performed for aluminum beam with bonded piezoelectric transducer (PZT). Modeled structure was excited to vibrate at high frequency range and electromechanical impedance (EMI) plots were obtained from the harmonic analysis. Notches were introduced in the beam and the damage metrics were used to asses qualitative changes in structural properties of the system. Furthermore, a parametric study of the effects of different variables was carried out. The numerical results show a good agreement was observed.

Abstract: The paper presents an application of resistive ladder sensors (or resistive crack gages) for health monitoring of an aircraft structure. An experiment was conducted during a Full Scale Fatigue Test (FSFT) of PZL 130 ORLIK TC II turbo-prop military trainer. The sensor can be successively used to detect and quantify fatigue cracks. It is a parametric transducer, similar to foil strain gages. Differences in shape of the measuring grid can be noticed. Principle of operation, sensor’s characteristics as well as block diagram of measurement system is presented in the paper. Also examples, both laboratory and FSFT data are delivered to prove surface crack detection capabilities. Simultaneously with new data collection, some investigation is carried out, connected with customize hardware elaboration, signal processing and structure-sensor integration method, what is briefly described.

Abstract: The paper presents an approach to develop a system for fatigue crack growth monitoring and early damage detection in the PZL – 130 ORLIK TC II turbo-prop military trainer aircraft structure. The system functioning is based on elastic waves propagation excited in the structure by piezoelectric PZT transducers. In the paper, a built block approach for the system design, signal processing as well as damage detection is presented. Description of damage detection capabilities are delivered in the paper and some issues concerning the proposed signal processing methods and their application to crack growth estimation models are discussed. Selected preliminary results obtained during the Full Scale Fatigue Test thus far are also presented.