Imperial College London

DrZahraSharif Khodaei

Faculty of EngineeringDepartment of Aeronautics

Reader in Structural Integrity
 
 
 
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Contact

 

+44 (0)20 7594 5116z.sharif-khodaei

 
 
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Location

 

329City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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111 results found

Giannakeas IN, Khodaei ZS, Aliabadi MH, 2022, Digital clone testing platform for the assessment of SHM systems under uncertainty, MECHANICAL SYSTEMS AND SIGNAL PROCESSING, Vol: 163, ISSN: 0888-3270

Journal article

Lambinet F, Khodaei ZS, 2021, Development of Hybrid Piezoelectric-Fibre Optic Composite Patch Repair Solutions, SENSORS, Vol: 21

Journal article

Yue N, Khodaei ZS, Aliabadi MH, 2021, Damage detection in large composite stiffened panels based on a novel SHM building block philosophy, SMART MATERIALS AND STRUCTURES, Vol: 30, ISSN: 0964-1726

Journal article

Goossens S, Berghmans F, Sharif Khodaei Z, Lambinet F, Karachalios E, Saenz-Castillo D, Geernaert Tet al., 2021, Practicalities of BVID detection on aerospace-grade CFRP materials with optical fibre sensors, Composite Structures, Vol: 259, Pages: 1-12, ISSN: 0263-8223

Several reports have recently shown the capability of optical fibre sensors for the detection of barely visible impact damage (BVID) on CFRP laminates, based on changes in the optical signal before and after impact. Although this approach was shown to work well in lab conditions, little attention has been paid so far to its practicality when considering realistic ambient conditions or to the detection range. In this work we attempt to derive BVID detection thresholds for fibre Bragg grating-based sensors, by considering standardized temperature and vibration levels for aerospace applications. To the best of our knowledge this is the first practical threshold assessment for BVID detection on aerospace-grade CFRP for such sensors. We have put our detection thresholds to the test by analysing a total of 24 BVIDs on 12 panels made from 4 different CFRP material systems and derived commendable sizes for the detection range on the different material systems.

Journal article

Pant S, Sharif Khodaei Z, Droubi MG, 2021, Monitoring Tasks in Aerospace, Springer Aerospace Technology, Pages: 5-14

Approximately up to one-fifth of the direct operating cost of a commercial civilian fixed-wing aircraft is projected to be due to inspection and maintenance alone. Managing aircraft health with minimal human intervention and technologies that can perform continuous or on-demand monitoring/evaluation of aircraft components without having to take the aircraft out of service can have a significant impact on increasing availability while reducing maintenance cost. The ambition of these monitoring technologies is to shift aircraft maintenance practice from planned maintenance (PM), where the aircraft is taken out of service for scheduled inspection/maintenance, to condition-based maintenance (CBM), where aircraft is taken out of service only when maintenance is required, while maintaining the required levels of safety. Structural health monitoring (SHM) techniques can play a vital role in progressing towards CBM practice. Therefore, this chapter aims to provide the reader with a brief overview of the different SHM techniques and their use, as well as, challenges in implementing them for aircraft applications.

Book chapter

Goossens S, Geernaert T, Khodaei ZS, Karachalios E, Saenz-Castillo D, Berghmans Fet al., 2021, Barely visible impact damage detection and location on composite materials by surface mounted and embedded aerospace-compatible optical fibre Bragg grating sensors, Conference on Optical Sensing and Detection VI, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X

Conference paper

Sharif Khodaei Z, Grigg S, 2021, Aerospace Requirements, Springer Aerospace Technology, Pages: 73-85

This chapter covers the overview of requirements arising in the aerospace industry for operating a structural health monitoring (SHM) system. The requirements are based on existing standards and guidelines and include both requirements on the physical components of the system (such as sensors, data acquisition systems and connectors) and their functional requirements (such as reliability, confidence measure and probability of detection). Emphasis has been given to on-board and ground-based components because they have different functionality requirements. An important factor in the reliability of the system is the effect of the environment and operational loads on the reliability of the diagnosis and, consequently, prognosis. The recommended guidelines for testing the reliability of the system under varying operational conditions are presented. This chapter is then finalized by reporting on methodologies for optimal sensor number and placement, based on different sensor technologies and different optimization algorithms.

Book chapter

Lopes JAG, Bacarreza O, Khodaei ZS, 2020, Design and Analysis of Composite Window Frame for a Regional Aircraft, JOURNAL OF MULTISCALE MODELLING, Vol: 11, ISSN: 1756-9737

Journal article

Lambinet F, Khodaei ZS, 2020, Damage detection & localization on composite patch repair under different environmental effects, ENGINEERING RESEARCH EXPRESS, Vol: 2, ISSN: 2631-8695

Journal article

Morse L, Khodaei ZS, Aliabadi MH, 2020, Reliability-based fracture analysis for plate bending problems with the dual boundary element method, FRACTURE AND DAMAGE MECHANICS: Theory, Simulation and Experiment, Publisher: AIP Publishing, Pages: 1-7

A novel methodology is presented for the efficient reliability analysis of plate structures containing cracks with the Dual Boundary Element Method (DBEM). The derivatives of the DBEM plate formulations for the Crack Surface Displacement Extrapolation (CSDE) method have been derived for the first time and are used as part of an Implicit Differentiation Method (IDM) for the efficient calculation of Stress Intensity Factor (SIF) sensitivities. A numerical example is investigated in which results from the presented CSDE methodology are compared to those from the J-integral. The SIF sensitivities were used with the First-Order Reliability Method (FORM) to determine the reliability of a plate structure containing a crack. Results indicate that the proposed CSDE methodology is capable of providing estimates for reliability that are very similar to those provided by the J-integral. Given that the proposed CSDE methodology can be easier to implement, it could prove to be an effective alternative to the J-integral for the efficient reliability analysis of plate structures containing cracks.

Conference paper

Giannakeas IN, Sharif-Khodaei Z, Aliabadi MH, 2020, Assessment of the performance of different element types for guided wave simulations in abaqus, FRACTURE AND DAMAGE MECHANICS: Theory, Simulation and Experiment, Publisher: American Institute of Physics, Pages: 1-10, ISSN: 1551-7616

Accurate numerical tools for the simulation of wave propagation are essential for the development and optimization of guided wave based Structural Health Monitoring systems. This article aims in delivering a systematic comparison of the Finite Element simulation of Lamb wave propagation using different types of elements. The numerical simulations are all realized within the environment of the commercial software Abaqus. In total three different element types are considered: conventional shell, continuum shell and 3D solid elements. To evaluate the performance of each element type, the numerically simulated signals are compared with experimental measurements from two panels. The first panel is made of Aluminium while the second is a layered composite panel. When continuum or 3D solid elements are used, the numerical predictions are closely correlated to the experimental observations. Accurate predictions were also made using conventional shell elements to model wave propagation in the first panel however, the group velocity for the first symmetric wave mode is over-estimated for the second panel when the excitation frequency is fc = 250kHz.

Conference paper

Li J, Khodaei ZS, Aliabadi MH, 2020, Boundary element analysis of lamb wave scattering by a through-thickness crack in a plate, ISSN: 0094-243X

This paper aims to analyse Lamb-wave scattering by a through-thickness crack in a plate using the boundary element plate formulations. These formulations allow to discretize the plate boundaries including plate edges and crack surfaces using simple one-dimensional line elements. Since infinite nature of the plate can be rigorously treated using the boundary element method, truncation of the plate domain is avoided to model the infinite domain. The crack is modelled using an efficient dual boundary element method, which allows to treat the crack surfaces as extra plate boundaries. The detailed scattering process is illustrated using snapshots at different time points.

Conference paper

Ceri S, Bacarreza O, Khodaei ZS, 2020, SPH, FEM and FEM-SPH numerical analysis of aluminium plate under low velocity impact, ISSN: 0094-243X

In the present paper, different numerical analyses are carried out for modelling impact events. Smooth Particle Hydrodynamics (SPH) formulations, Finite Element Method (FEM) and a coupled FEM-SPH models are performed to investigate the response of AA5083-H116 Aluminium plate subjected to low velocity impact (12.31 m/s). Dimensions of Aluminium plate is 300 x 300 x 5 mm. There are 16 types of SPH formulation are available in Ls-Dyna, however, 4 of them are recommended to use with solid structures which are Standard SPH formulation (FORM=0), Renormalized SPH formulation (FORM=1), Total Lagrangian Formulation (FORM=7) and Renormalized Total Lagrangian Formulations (FORM=8). For FEM-SPH modelling, SPH particles are modelled with renormalized SPH formulations. Johnson-Cook material model is used with Gruneisen Equation of State (EOS) for the Aluminium plate. The response to impact event of models contain maximum deflection which is validated by experimental data available in literature. The results show, Total Lagrangian behaviour and FEM-SPH coupling have good agreement with experimental data by less than 2% error. However, maximum deflection value of standard SPH formulations obtained has 18.07% error.

Conference paper

Giannakeas IN, Sharif-Khodaei Z, Aliabadi MH, 2020, On the estimation of material properties using guided wave measurements for the calibration of finite element models, ISSN: 0094-243X

The design and development of robust and reliable guided wave Structural Health Monitoring systems require accurate information of the structure's material properties. This is needed by various analysis tools for the determination of wave propagation characteristics in order to evaluate and optimize the system's performance. Estimation of the mechanical properties of composite materials using Lamb wave measurements is not straightforward as it requires the solution of an inverse problem. In this study, a numerical procedure is presented for the material properties estimation. The aim is to obtain estimates of the unknown material properties using circular surface mounted piezoelectric transducers that can be used for material characterization or calibration of numerical models. The procedure utilizes the Semi-analytical finite element method for the efficient computation of the dispersion curves and a genetic algorithm for the extraction of the material properties that fit best the experimental observations.

Conference paper

Morse L, Sharif Khodaei Z, Aliabadi MH, 2020, Statistical inference of the equivalent initial flaw size for assembled plate structures with the dual boundary element method, Engineering Fracture Mechanics, Vol: 238, ISSN: 0013-7944

The statistical inference of the Equivalent Initial Flaw Size Distribution (EIFSD) is developed for the first time using the Dual Boundary Element Method (DBEM) for assembled shear deformable plate structures. As part of this inference procedure, Bayesian updating is employed to enable the continuous refinement of the EIFSD via data obtained by many simulated routine inspections of a stiffened panel from a fleet of aircraft. Fatigue crack growth is modelled using an incremental crack growth procedure that only requires modelling of the boundary of the 2.5D structure with line elements and requires no remeshing during crack growth simulations. Stochastic Kriging is employed to account for the stochastic nature of fatigue crack growth and to offset the high computational cost associated with modelling complex built-up structures. To demonstrate the efficiency of the proposed inference methodology, a numerical example featuring a stiffened panel subjected to complex loading in the form of combined tension and bending is presented. Once the EIFSD has been inferred, it can be used to optimise the intervals between routine aircraft inspections via the use of reliability analysis techniques as part of a combined reliability-EIFS approach. It is demonstrated that the proposed methodology offers the capability to reduce the costs associated with inspections.

Journal article

Sharif Khodaei Z, Li J, Aliabadi MH, 2020, Boundary element modelling of ultrasonic Lamb waves for structural health monitoring, Smart Materials and Structures, Vol: 29, Pages: 1-19, ISSN: 0964-1726

In this paper, a novel boundary element plate formulation is proposed to model ultrasonic Lamb waves in both pristine and cracked plates for structural health monitoring (SHM) applications. Lamb waves are generated and sensed by piezoelectric discs. An equivalent pin-force model is newly proposed to represent the actuation effect of piezoelectric discs, which is more accurate than the classical pin-force model. The boundary element formulation is presented in the Laplace-transform domain based on plate theories, which allows three-dimensional analysis of Lamb wave behaviours, such as propagation and interaction with cracks, in thin-walled structures. A damage detection algorithm is used for crack localization alongside the BEM-simulated data. The BEM solutions show excellent agreement with both 3D finite element simulation and experimental results.

Journal article

Xu C, Sharif Khodaei Z, 2020, Shape sensing with Rayleigh backscattering fibre optic sensor, Sensors, Vol: 20, ISSN: 1424-8220

In this paper, Rayleigh backscattering sensors (RBS) are used to realize shape sensing of beam-like structures. Compared to conventional shape sensing systems based on fibre Bragg grating (FBG) sensors, RBS are capable of continuous lateral sensing. Compared to other types of distributed fibre optic sensors (FOS), RBS have a higher spatial resolution. First, the RBS’s strain sensing accuracy is validated by an experiment comparing it with strain gauge response. After that, twoshapesensingalgorithms(thecoordinatetransformationmethod(CTM)andthestrain-deflection equationmethod(SDEM))basedonthedistributedFOS’inputstraindataarederived. Thealgorithms arethenoptimizedaccordingtothedistributedFOS’features,tomakeitapplicabletocomplexand/or combine loading situations while maintaining high reliability in case of sensing part malfunction. Numerical simulations are carried out to validate the algorithms’ accuracy and compare their accuracy. The simulation shows that compared to the FBG-based system, the RBS system has a better performance in configuring the shape when the structure is under complex loading. Finally, avalidationexperimentisconductedinwhichtheRBS-basedshapesensingsystemisusedtoconfigure the shape of a composite cantilever-beam-like specimen under concentrated loading. The result is then compared with the optical camera-measured shape. The experimental results show that both shape sensing algorithms predict the shape with high accuracy comparable with the optical camera result.

Journal article

Dafydd I, Sharif Khodaei Z, 2020, Analysis of barely visible impact damage severity with ultrasonic guided Lamb waves, Structural Health Monitoring, Vol: 19, Pages: 1104-1122, ISSN: 1475-9217

Barely visible impact damage is one of the most common types of damage in carbon-fibre-reinforced polymer composite structures. This article investigates the potential of using ultrasonic guided Lamb waves to characterise the through thickness severity of barely visible impact damage in thin carbon-fibre-reinforced polymer structures. In the first step, a laser Doppler vibrometer was used to capture the full damage interaction of the wavefield excited by a piezoelectric actuator. Damage-scattered wavefield for four different severities were studied to find the best parameters for characterising the severity of damage. To reduce the overall acquisition time and size of data collected using the laser Doppler vibrometer, the measured signals were reconstructed from a singular broadband chirp response using a post-processing algorithm. From the full wavefield analysis obtained at a wide range of toneburst frequencies, the results showed that barely visible impact damage severity could be characterised using ultrasonic guided Lamb waves and that the 𝐴0 mode, dominant at lower frequencies, gave better results than the 𝑆0 mode. In the second step, the parameters for characterising the damage severity were applied to a sparse network of transducers as an in-service structural health monitoring methodology. The damage was successfully detected and located. In addition, the transducer path close to the predicted damage location was utilised to successfully quantify the damage severity based on the proposed damage index.

Journal article

Xu C, Sharif Khodaei Z, 2020, A novel fabry-pérot optical sensor for guided wave signal acquisition, Sensors, Vol: 20, Pages: 1728-1728, ISSN: 1424-8220

In this paper, a novel hybrid damage detection system is proposed, which utilizes piezoelectric actuators for guided wave excitation and a new fibre optic (FO) sensor based on Fabry-Perot (FP) and Fiber Bragg Grating (FBG). By replacing the FBG sensors with FBG-based FP sensors in the hybrid damage detection system, a higher strain resolution is achieved, which results in higher damage sensitivity and higher reliability in diagnosis. To develop the novel sensor, optimum parameters such as reflectivity, a wavelength spectrum, and a sensor length were chosen carefully through an analytical model of the sensor, which has been validated with experiments. The sensitivity of the new FBG-based FP sensors was compared to FBG sensors to emphasize the superiority of the new sensors in measuring micro-strains. Lastly, the new FBG-based FP sensor was utilized for recording guided waves in a hybrid setup and compared to the conventional FBG hybrid sensor network to demonstrate their improved performance for a structural health monitoring (SHM) application.

Journal article

Tabian I, Fu H, Khodaei ZS, 2020, Impact detection on composite plates based on convolution neural network, Pages: 476-481, ISSN: 1013-9826

This paper presents a novel Convolutional Neural Network (CNN) based metamodel for impact detection and characterization for a Structural Health Monitoring (SHM) application. The signals recorded by PZT sensors during various impact events on a composite plate is used as inputs to CNN to detect and locate impact events. The input of the metamodel consists of 2D images, constructed from the signals recorded from a network of sensors. The developed meta-model was then developed and tested on a composite plate. The results show that the CNN-based metamodel is capable of detecting impacts with more than 98% accuracy. In addition, the network was capable of detecting impacts in the other regions of the panel, which was not trained with but had similar geometric configuration. The accuracy in this case was also above 98%, showing the scalability of this method for large complex structures of repeating zones such as composite stiffened panel.

Conference paper

Li J, Sharif Khodaei Z, Aliabadi FMH, 2019, Dynamic fracture analysis of plates loaded in tension and bending using the dual boundary element method, Advances in Fracture and Damage Mechanics XVIII, Publisher: Trans Tech Publications, Ltd., Pages: 440-445

The purpose of this paper is to solve dynamic fracture problems of plates under both tension and bending using the boundary element method (BEM). The dynamic problems were solved in the Laplace-transform domain, which avoided the calculation of the domain integrals resulting from the inertial terms. The dual boundary element method, in which both displacement and traction boundary integral equations are utilized, was applied to the modelling of cracks. The dynamic fracture analysis of a plate under combined tension and bending loads was conducted using the BEM formulations for the generalized plane stress theory and Mindlin plate bending theory. Dynamic stress intensity factors were estimated based on the crack opening displacements.

Conference paper

Bekas DG, Mendias MM, Sharif Khodaei Z, Karachalios E, Alonso FJC, Aliabadi FMHet al., 2019, SHM of composite mono-stringer elements based on guided waves, Advances in Fracture and Damage Mechanics XVIII, Publisher: Trans Tech Publications, Ltd., Pages: 464-469

In this work, the applicability of structural health monitoring (SHM) technique for damage detection in two composite mono-stringers representative of composite fuselage are investigated. The two different manufacturing technologies are co-curing and co-bonding of composite mono-stringers to the skin. The panels were then impacted at the foot of the stringer to cause Barely Visible Impact Damage (BVID). Piezoelectric transducers were surface mounted on the mono-stringers, guided wave measurements before and after impact were taken and used for detecting damage based on Weighted Energy Arrival Method (WEAM).

Conference paper

Bekas DG, Saenz-Castillo D, Sharif Khodaei Z, Alonso FJC, Aliabadi FMHet al., 2019, Smart bondline monitoring of an efficient industrial thermoplastic aircraft window frame, Advances in Fracture and Damage Mechanics XVIII, Publisher: Trans Tech Publications, Ltd., Pages: 470-475

In this work, a smart thermoplastic window frame for a regional aircraft has been designed and manufactured. The aim of the work was to design a smart sensing system for monitoring of a bonded thermoplastic aircraft window frame in operation. The conductive tracks were designed and inkjet-printed onto the window frame and their disruption was used as an indication of a damage event created within the bondline. Based on the electrical resistance measurements, the method was able to detect a damage that was created in the bondline due to an impact event. To verify the proposed methodology, ultrasonic C-scan inspection was also performed.

Conference paper

Iuliana T, Fu H, Sharif Khodaei Z, 2019, A convolutional neural network for impact detection and characterization of complex composite structures, Sensors, Vol: 19, ISSN: 1424-8220

This paper reports on a novel metamodel for impact detection, localization and characterization of complex composite structures based on Convolutional Neural Networks (CNN) and passive sensing. Methods to generate appropriate input datasets and network architectures for impact localization and characterization were proposed, investigated and optimized. The ultrasonic waves generated by external impact events and recorded by piezoelectric sensors are transferred to 2D images which are used for impact detection and characterization. The accuracy of the detection was tested on a composite fuselage panel which was shown to be over 94%. In addition, the scalability of this metamodelling technique has been investigated by training the CNN metamodels with the data from part of the stiffened panel and testing the performance on other sections with similar geometry. Impacts were detected with an accuracy of over 95%. Impact energy levels were also successfully categorized while trained at coupon level and applied to sub-components with greater complexity. These results validated the applicability of the proposed CNN-based metamodel to real-life application such as composite aircraft parts.

Journal article

Li J, Khodaei ZS, Aliabadi MH, 2019, Dynamic fracture analysis of Kane–Mindlin plates using the dual boundary element method, Engineering Analysis with Boundary Elements, Vol: 106, Pages: 217-227, ISSN: 0955-7997

In this paper, a new dual boundary element formulation is presented for dynamic crack problems in finite-thickness plates under in-plane loadings. The proposed formulation is based on a first-order plate theory (Kane–Mindlin theory) taking into account a coupled out-of-plane fracture mode due to in-plane shear loading and the effect of plate thickness on stress intensity factors, which cannot be considered within the framework of the two-dimensional elastic theories. The dynamic stress intensity factors are evaluated based on the crack opening displacements. Three benchmark examples are presented including the mixed-mode fracture of a finite plate. The effect of plate thickness on the dynamic stress intensity factors is investigated. The dynamic stress intensity factors obtained using the proposed formulation are shown to be in good agreement with the results from 3D finite element simulations.

Journal article

Morse L, Sharif Khodaei Z, Aliabadi MH, Morse L, Sharif Khodaei Z, Aliabadi MHet al., 2019, A dual boundary element based implicit differentiation method for determining stress intensity factor sensitivities for plate bending problems, Engineering Analysis with Boundary Elements, Vol: 106, Pages: 412-426, ISSN: 0955-7997

A novel methodology for determining Stress Intensity Factor (SIF) sensitivities for plate bending problemsusing the Dual Boundary Element Method (DBEM) is presented. The direct derivatives of the DBEM integralequations for plate bending have been derived for the first time and are used as part of a DBEM-based ImplicitDifferentiation Method (IDM or DBEM-IDM) for calculating the sensitivities of SIFs to changes in differentgeometric parameters such as crack length and crack rotation angle. The SIFs and their sensitivities arecalculated using the J-integral and the derivative of the J-integral respectively. A numerical example featuringa thick plate subjected to membrane, bending, and pressure loads is presented. In the first half of the numericalexample, the SIF sensitivities from the IDM are compared with those obtained from the more common, butrelatively crude, Finite Difference Method (FDM or DBEM-FDM). Results show that the IDM is a significantlymore efficient and robust alternative to the FDM. The accuracy of the FDM showed significant dependence onthe step size used, necessitating a time-consuming optimization procedure to determine the optimal step size.Once this optimal step size was found, both methods provided very similar results. As part of the second halfof the numerical example, a demonstration of one possible application of the SIF sensitivities from the IDMis presented. This involved carrying out reliability analyses using the First-Order Reliability Method (FORM)with a large number of design variables.

Journal article

Seno AH, Sharif Khodaei Z, Aliabadi MHF, 2019, Passive sensing method for impact localisation in composite plates under simulated environmental and operational conditions, Mechanical Systems and Signal Processing, Vol: 129, Pages: 20-36, ISSN: 0888-3270

A novel feature extraction method is developed for impact localisation based on Artificial Neural Networks (ANNs) in sensorized composite structures subjected to environmental and operational conditions. Impact induced lamb waves are investigated for the first time for different impact scenarios (angle, mass and energy) on flat and curved plates under environmental (temperature range) and operational (vibration) conditions. The Time of Arrival (TOA) is significantly influenced by these conditions hence complicating the impact localisation. To overcome this complication, a novel and robust TOA extraction method is proposed. It is based on Normalised Smoothed Envelope Threshold (NSET) coupled with a high pass filter to remove vibration noise prior to TOA extraction. Localisation ANNs were trained with data from a single baseline impact condition and were tested under impacts with varying conditions. It was shown that by using the proposed method for TOA extraction, the trained ANN is able to better predict the location of impacts compared to an ANN trained with data from common TOA extraction methods (detection area 0.99–56.08% of sensing region versus 0.28–1.55% for NSET). The developed method gives consistent accuracy and significantly reduces the required training data, making ANN based impact localisation more feasible for real life application.

Journal article

Fu H, Sharif Khodaei Z, Aliabadi M, 2019, An energy-efficient cyber-physical system for wireless on-board aircraft structural health monitoring, Mechanical Systems and Signal Processing, Vol: 128, Pages: 352-368, ISSN: 0888-3270

In this paper, an energy-efficient cyber-physical system using piezoelectric transducers (PZTs) and wireless sensor networks (WSN) is proposed, designed and experimentally validated for on-board aircraft structural health monitoring (SHM). A WSN is exploited to coordinate damage detection using PZTs distributed on the whole aircraft. An active sensing methodology is adopted for PZTs to evaluate the structural integrity in a pitch-catch manner. The system configuration and operation principle are discussed in the first place. Then, the detailed hardware design was introduced. The proposed system is not only characterized as low-power, high-compactness and wireless, but also capable of processing actuating-sensing signals at megahertz, generating actuating signals with great flexibility, handling multiple actuating-sensing channels with marginal crosstalk. The design was implemented on a 4-layer printed circuit board (8 × 6.5 cm) and evaluated on a large-scale composite fuselage. A 5 MHz sampling rate for actuating and 1.8 MHz for sensing (8 channels) were realized, and the accuracy was validated by comparing the results with those from an oscilloscope. The crosstalk issue caused by actuation on sensing channels is properly addressed using a 2-stage attenuation method. An ultra-low current (81.7 μA) was measured when no detection was required; the average current was 0.45 mA with a detection rate of twice per hour, which means the system can continuously work for up to 12.6 months for 2 AA batteries. Eventually, an example of damage detection is provided, showing the capability of such a system in SHM.

Journal article

Bekas DG, Sharif Khodaei Z, Aliabadi MH, 2019, A smart multi-functional printed sensor for monitoring curing and damage of composite repair patch, Smart Materials and Structures, Vol: 28, ISSN: 0964-1726

A novel multifunctional diagnostic sensor is developed as a cost-effective, in-service structural health monitoring (SHM) system for determining the initial quality of curing of a bonded composite repair patch and assessing its long-term durability on composite structure. The proposed multi-functional sensor technology involves the creation of a "tailor-to-order" 2D conductive patterns onto step-sanded repair surface of composite repair patch using inkjet printing. In employing this methodology, bondline quality during curing and in service was successfully assessed via Impedance spectroscopy and resistance change measurements, respectively. The ability of this technology to effectively monitor the integrity of the bondline and the extent of damage in real-time was investigated by subjecting the scarf-repaired CFRP panels to 3-point bending fatigue and low-velocity impact tests. The obtained results were compared with those of transient infrared thermography (IrT) and ultrasound inspection techniques, thus validating the proposed method.

Journal article

Morse L, Sharif Khodaei Z, Aliabadi M, 2019, A multi-fidelity boundary element method for structural reliability analysis with higher-order sensitivities, Engineering Analysis with Boundary Elements, Vol: 104, Pages: 183-196, ISSN: 0955-7997

A novel multi-fidelity modelling methodology for structural reliability analysis using the Boundary Element Method (BEM) with an Implicit Differentiation Method (IDM) is presented. The higher-order sensitivities of the elastostatic BEM equations with respect to changes in several geometric variables have been derived for the first time for use with theIDM for conducting reliability analyses with the Second-Order Reliability Method (SORM), a more accurate alternative to FORM for problems with non-linear limit state functions. Multi-fidelity formulations involving the IDM have also been derived for the first time, making use of the metamodeling technique Kriging. The use of multi-fidelity modellingenables the creation of a model that has similar accuracy to a high-fidelity model, but with a computational cost similar to that of a low-fidelity model. The IDM is validated through a numerical example for which the analytical solution is known. A further two examples featuring an I-beam section and a triangular support bracket with a large number of variables are also investigated. Overall, it has been shown that the proposed IDM/multi-fidelity modelling methodology significantly improved the efficiency and accuracy of the reliability analyses when applied to complex problems involving a large number of random variables under high levels of uncertainty.

Journal article

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