Publications
401 results found
Rodriguez-Tembleque L, Saez A, Aliabadi MH, 2016, Indentation response of piezoelectric films under frictional contact, International Journal of Engineering Science, Vol: 107, Pages: 36-53, ISSN: 0090-6913
Piezoelectric materials are available in a variety of shapes and forms in smart systems. One of the most common shapes for sensor or actuator applications is the film form. To gain a better understanding of the indentation behavior of these systems, this work analyzes piezoelectric films under different 3D frictional contact boundary conditions. For this purpose, the boundary element formulation presented by authors in Rodríguez-Tembleque, Buroni, and Sáez (2015) is used for modeling piezoelectric finitely thick and thin films under orthotropic frictional indentation conditions, including tangential loads. The formulation has been applied to analyze the influence of friction and tangential loads on the electromechanical response of finitely thick piezoelectric films, ranging from a piezoelectric half space configuration, where the contact radius is much smaller than the thickness of the film, to a thin film configuration. Results reveal that these variables have to be considered to study the indentation response of these advanced systems. In other case, we could over- or underestimate the piezoelectric response and its distribution over the contact zone.
Mantic V, Saez A, Aliabadi MH, 2016, International conference on boundary element and meshless techniques XVI PREFACE, European Journal of Computational Mechanics, Vol: 25, Pages: 1-1, ISSN: 1779-7179
Salmanpour MS, Sharif Khodaei Z, Aliabadi MH, 2016, Transducer placement optimisation scheme for a delay and sum damage detection algorithm, Structural Control and Health Monitoring, Vol: 24, ISSN: 1545-2255
In this work, a transducer placement scheme based on wave propagation is proposed, which enhances damage localisation. The method was tailored to seek an optimal transducer network placement for a delay and sum damage detection algorithm. The proposed method determines a coverage index map and utilises a genetic algorithm to determine an optimal transducer network. It can also minimise the impact of faulty transducers, incorporate the effect of stiffeners and different damage types. The method is initially verified using numerically simulated signals. The optimal network outperformed the suboptimal for detection of holes and debonding in a stiffened panel. It is also shown that the coverage index reflected the localisation accuracy. The method is then validated with experimental results and the generated optimal transducer network compared with a suboptimal arrangement. The optimal network is shown to locate an actual crack with significantly higher accuracy than the suboptimal arrangement.
Salmanpour MS, Sharif khodaei, Aliabadi MH, 2016, Guided wave temperature correction methods in structural health monitoring, Journal of Intelligent Material Systems and Structures, Vol: 28, Pages: 604-618, ISSN: 1530-8138
In this paper a method for addressing temperature effects using Lamb waves is developed withapplication to baseline comparison damage detection. The proposed method is based on baseline signal stretchwith an improved minimum residual allowing correction over a larger temperature range. The effectiveness ofthe proposed approach in detecting (artificial) damages is demonstrated experimentally over a large temperature.The method is also shown to accurately detect and localise a crack in an aluminium panel and actual impactdamage on a CFRP panel.
Rodriguez-Tembleque L, Buroni FC, Saez A, et al., 2016, 3D coupled multifield magneto-electro-elastic contact modelling, International Journal of Mechanical Sciences, Vol: 114, Pages: 35-51, ISSN: 1879-2162
The present work deals with the general contact problem for coupled magneto-electro-elastic materials. Despite of the relevant technological applications, this topic of research has been treated only in some analytical works. But analytical solutions lack the generality of numerical methodologies, being restricted typically to simple geometries, loading conditions, idealized contact conditions and mostly taking into account transversely isotropic material symmetry with the symmetry axis normal to the contact surface. In this work, a numerical procedure for the three-dimensional frictional contact modelling of anisotropic coupled magneto-electro-elastic materials in presence of both electric and magnetic fields is presented for the first time. An orthotropic frictional law is considered, so anisotropy is present both in the bulk and in the surface. The methodology uses the boundary element method with explicit evaluation of the fundamental solutions in order to compute the magneto-electro-elastic influence coefficients. The contact model is based on an augmented Lagrangian formulation and it uses an iterative Uzawa scheme of resolution. Conducting, semi-conducting and insulated electric and/or magnetic indentation conditions, as well as orthotropic frictional contact conditions are considered. The methodology is validated by comparison with benchmark analytical solutions. Then, additional exploration examples are presented and discussed in detail, revealing that magneto-electric material coupling, conductivity contact conditions lead to a significant effect on the indentation force and contact pressure distributions. The influence of friction in electric and magnetic potential responses has been also proved to be very significant. Moreover, tangential loads exhibit an important influence both on the maximum values of the electric and magnetic potentials as well as on their distributions.
Sharif-Khodaei Z, Ghajari M, Aliabadi MH, 2016, Impact damage detection in composite plates using a self-diagnostic electro-mechanical impedance-based structural health monitoring system, Journal of Multiscale Modelling, Vol: 6, ISSN: 1756-9737
In this work, application of the electro-mechanical impedance (EMI) method in structural health monitoring as a damage detection technique has been investigated. A damage metric based on the real and imaginary parts of the impedance measures is introduced. Numerical and experimental tests are carried out to investigate the applicability of the method for various types of damage, such as debonding between the transducers and the plate, faulty sensors and impact damage in composite plates. The effect of several parameters, such as environmental effects, frequency sweep, severity of damage, location of damage, etc., on the damage metric has been reported.
Salmanpour MS, Sharif Khodaei Z, Aliabadi MH, 2016, TOWARDS REAL-TIME STRUCTURAL HEALTH MONITORING DAMAGE DETECTION WITHOUT USER INPUT, ECCOMAS Congress 2016
In this work a real-time damage detection platform is presented, requiring little tono user input after initial installation and set-up. Diagnostic ultrasonic signals are generatedusing attached piezoelectric transducers, which also serve to capture the structural response.This paper shows real-time detection in a flat CFRP panel. The necessary data acquisitionand signal processing is carried out in an automated manner. A visualization of the damagemap is then given as the primary output highlighting the predicted damage location. The developedsystem is flexible in allowing scalable deployment to cater for an increased numberof transducers. The detection platform is experimentally demonstrated by real-time localizationof artificial damages at various locations on a CFRP panel. This was also done underoperational environment vibration loading, yielding accurate damage localization.
RodrÃguez-Tembleque L, Aliabadi MH, 2016, Numerical simulation of fretting wear in fiber-reinforced composite materials, Engineering Fracture Mechanics, ISSN: 0013-7944
Computational modeling of fretting wear in fiber-reinforced composite materials is a difficult task due to the fact that contact and wear constitutive laws require considering micromechanical aspects such as the fiber orientation relative to the sliding direction or the fiber volume fraction. In this work, a 3D Boundary Element Method formulation for wear modeling is proposed and applied to simulate fretting-wear in fiber-reinforced composites. New contact constitutive laws for friction and wear modeling in fiber-reinforced composites are incorporated to an augmented Lagrangian resolution scheme and applied to compute and study wear in a carbon FRP film.
López C, Bacarreza O, Baldomir A, et al., 2016, Reliability-Based optimization of the stacking sequence layup in post- Buckled composite stiffened panels, Pages: 22-25, ISSN: 1013-9826
This paper presents a methodology to carry out Reliability-Based Design Optimization (RBDO) in composite stiffened panels. The target is to maximize the reaction force that the panel can withstand before collapse, setting the shortening of failure as the probabilistic constraint. The design variables are the stacking sequence orientations of the composite plies while the random parameters are the elastic properties of the material. In order to predict the collapse load properly, post-buckling and progressive failure analyses are considered within the FE solver employed.
Yue N, Khodaei ZS, Aliabadi MH, 2016, Passive sensing of sensorized composite panels: Support vector machine, Pages: 199-202, ISSN: 1013-9826
Strain readings recorded by surface mounted piezoelectric sensors due to impact events on composite panel are used to detect and characterize the impact. Sensor signals on a composite stiffened panels have been simulated by a valid numerical model. Applicability of least square support vector machines (LSSVM) on creating a meta-model to detect and characterize impact event has been investigated. In particular, the main advantage of LSSVM over other meta-modeling technique was found to be the smaller number of training data that is required. Experimental results on a composite panel has been used to validate the findings.
Thiene M, Khodaei S, Aliabadi MH, 2016, Uncertainty analysis of active SHM system, Pages: 249-252, ISSN: 1013-9826
Structural Health Monitoring (SHM) techniques have gained an increased interest to be utilised alongside NDI techniques for aircraft maintenance. However, to take the SHM methodologies from the laboratory conditions to actual structures under real load conditions requires them to be assessed in terms of reliability and robustness. In this work, a statistical analysis is carried out for an SHM system for damage detection and characterisation in composite structures. The sensitivity of the platform to parameters such as noise, sensor failure, placement tolerances and bonding has been investigated and reported.
Lambinet F, Khodaei ZS, Aliabadi MH, 2016, Structural health monitoring of bonded patch repaired composite, Pages: 135-138, ISSN: 1013-9826
Bonded repair of composite structures still remains a crucial concern for the airworthiness authorities because of the uncertainty about the repair quality. This works, investigates the applicability of Structural Health Monitoring (SHM) techniques for monitoring of bonded repair. Active sensing method has been applied to two case studies: A sensorised panel impacted to cause barely visible impact damage (BVID) and repaired afterwards, the tensile and fatigue testing of a composite strap repair. In the first case, the previous sensors have been used to detect an artificially introduced damage. In the second case the failure of the adhesive during the tensile testing is used as basis of the load levels in the tensile-Tensile fatigue test. In both cases PZT transducers have been used to monitor the bonded patch. An electromechanical impedance (EMI) and Lamb wave analysis have been carried out to check the overall integrity of the repair patch between. In both cases the state of the repaired composite was monitored successfully and reported.
Sainfort L, Khodaei ZS, Aliabadi MH, 2016, Optimal sensor positioning for damage detection in composite sensorised panels, Pages: 191-194, ISSN: 1013-9826
In this work the optimal configuration of transducers for damage detection and localization has been investigated. A particular interest is given to three optimization methods: mini-max, average Probability of Non Detection (POND) and ray tracing approach, coupled with genetic algorithm. After optimal configurations have been computed for each technique, they are experimentally tested and compared on a composite panel with one or two damages by generating and receiving Lamb waves signals. Damage detection is carried out with the Probability Based Damage Index Method (PBDIM). It was found that, in most cases, the ray tracing method and the average POND technique give better results, with a good detection of damages in comparison to the minimax POND technique, even if the latter seems numerically better.
Thiene M, Sharif Khodaei Z, Aliabadi MH, 2016, Optimal sensor placement for damage detection based on ultrasonic guided wave, Pages: 269-272, ISSN: 1013-9826
In this work a methodology for effective positioning of sensors and actuators for damage detection and characterisation is described. The novelty of the proposed methodology is that the fitness function to be optimised does not contain probability of detection (POD) which needs to be obtained for every possible sensor combination. The proposed fitness function is to provide the maximum coverage of the structure via Lamb waves and reduce the negative effects of boundary reflections. Once the fitness function is defines, genetic algorithm (GA) is used as an optimisation strategy to result in optimal sensor positioning.
Khodaei ZS, Aliabadi MH, 2016, An optimization strategy for best sensor placement for damage detection and localization in complex composite structures, Pages: 2999-3008
In this paper an optimization strategy based on providing maximum area coverage (MAC) resulting in optimal sensor placement for damage localization in complex composite structures is proposed. The proposed optimization algorithm is uses genetic algorithm to minimize the defined fitness function based on geometrical and physical constraints of the structure, rather than probability of detection of the damage detection algorithm. The proposed fitness function is applicable to any damage detection technique based on ultrasonic guided wave in pitch catch configurations and is readily up-scalable to any structure. The optimization algorithm is then applied to a full wing demonstrator of an aircraft.
Thiene M, Khodaei ZS, Aliabadi MH, 2016, Statistical analysis of SHM passive sensing systems, Pages: 241-244, ISSN: 1013-9826
Structural Health Monitoring (SHM) techniques have gained an increased interest to be utilised alongside NDI techniques for aircraft maintenance. However, to take the SHM methodologies from the laboratory conditions to actual structures under real load conditions requires them to be assessed in terms of reliability and robustness. In this work, a statistical analysis is carried out for a passive SHM system capable of impact detection and identification. The sensitivity of the platform to parameters such as noise, sensor failure and in-service load conditions has been investigated and reported.
De Luca A, Sharif-Khodaei Z, Aliabadi MH, et al., 2016, Numerical simulation of the Lamb wave propagation in impacted CFRP laminate, 2nd International Symposium on Dynamic Response and Failure of Composite Materials, (Draf), Publisher: ELSEVIER SCIENCE BV, Pages: 109-115, ISSN: 1877-7058
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- Citations: 21
Zou F, Aliabadi MH, 2015, A boundary element method for detection of damages and self-diagnosis of transducers using electro-mechanical impedance, SMART MATERIALS AND STRUCTURES, Vol: 24, ISSN: 0964-1726
Di Pisa C, Aliabadi MH, 2015, Boundary element analysis of stiffened panels with repair patches, Engineering Analysis with Boundary Elements, Vol: 56, Pages: 162-175, ISSN: 0955-7997
In this paper a boundary element method for analysis of fractured stiffened panels repaired with riveted or adhesively bonded patches is presented. In order to achieve such a formulation, several boundary element formulations involving the membrane and bending of displacement, and, stress resultants are coupled together to analyse the model. The multi-region formulation is used to simulate the stiffeners, which are modelled as an assembly. They are then connected to the sheets to form the stiffened panels by means of a rivet formulation. The dual boundary element method is used to simulate the presence of cracks, and the patches, treated as independent plates, are joined to the panel either with rivets or adhesive. A boundary element formulation for adhesive bonding is implemented to model the adhesively bonded patches. The Crack Opening Displacements (COD) method and the J-integral are implemented to evaluate the required fracture parameters. Examples presented include a wing box with a three spar section, with fully stiffened skin, and, the skin is considered to have a crack and a repair patch is used on top of the crack to stop its growth.
Benedetti I, Aliabadi MH, 2015, Multiscale modeling of polycrystalline materials: a boundary element approach to material degradation and fracture, Computer Methods in Applied Mechanics and Engineering, Vol: 289, Pages: 429-453, ISSN: 0045-7825
In this work, a two-scale approach to degradation and failure in polycrystalline materials is proposed. The formulation involves the engineering component level (macro-scale) and the material grain level (micro-scale). The macro-continuum is modeled using a three-dimensional boundary element formulation in which the presence of damage is formulated through an initial stress approach to account for the local softening in the neighborhood of points experiencing degradation at the micro-scale. The microscopic degradation is explicitly modeled by associating Representative Volume Elements (RVEs) to relevant points of the macro continuum, for representing the polycrystalline microstructure in the neighborhood of the selected points. A three-dimensional grain-boundary formulation is used to simulate intergranular degradation and failure in the microstructure, whose morphology is generated using the Voronoi tessellations. Intergranular degradation and failure are modeled through cohesive and frictional contact laws. To couple the two scales, macro-strains are transferred to the RVEs as periodic boundary conditions, while overall macro-stresses are obtained as volume averages of the micro-stress field. The comparison between effective macro-stresses for the damaged and undamaged RVE allows to define a macroscopic measure of material degradation. To avoid pathological damage localization at the macro-scale, integral non-local counterparts of the strains are employed. A multiscale processing algorithm is described. Two multiscale simulations are performed to demonstrate the capability of the method.
Meng S, Sharif Khodaei Z, Aliabadi MH, 2015, Localization of barely visible impact damage (BVID) in composite plates, Pages: 217-220, ISSN: 1013-9826
This paper exploits the implementation of a delay-and-sum imaging method using Lamb wave signals to localise barely visible impact damage (BVID) in quasi-isotropic composite panels. The structural discontinuities, such as opening and stiffener, has also been tested to reflect the common structural features of an aircraft and to examine the feasibility of the proposed detection technique. The prediction results are compared with ultrasonic C-scan images, which indicate location error for three different panels-flat panel, flat panel with an opening and stiffened panel. The accuracy is believed to be improved by increasing the number of transducers. Overall the proposed damage detection technique, with the use of only four transducers, demonstrated sufficient accuracy and efficiency in impact damage detection and can be applied alongside the traditional NDT inspections for providing a priori information of the impact damage location.
Sharif Khodaei Z, Aliabadi MH, 2015, Lamb-wave based damage detection in anisotropic composite plates, Pages: 1-4, ISSN: 1013-9826
Damage detection in anisotropic composite plates based on Lamb wave technique has been investigated. A network of transducers is used to detect barely visible damage caused by impact. A CFRP composite plate has been impacted and tested to verify the proposed damage detection algorithms. The difference in the propagational properties of Lamb waves in the pristine state and the damage state is used through data fusion and imaging algorithms to detect, locate and characterise the damage. The influence of directionality of the velocity on the validity of the detection algorithm is examined and some results are presented.
Thiene M, Sharif-Khodaei Z, Aliabadi MH, 2015, Comparison of artificial neural networks and the transfer function method for force reconstruction in curved composite plates, Pages: 301-304, ISSN: 1013-9826
This paper presents two of the most recent approaches for impact force reconstruction, applied to a curved composite panel. The first one is based on the development of an artificial neural network, while the other on the evaluation of transfer functions in the frequency domain. Both methods provide advantages and disadvantages so that a detailed study should be conducted in order to determine which one can be considered more suitable for impact identification purposes. The aim of this paper is to present a comparison between these two methods, in particular when impacts on different surfaces of the plate are present. The main contribution is the application of the two approaches on a curved composite panel. The radius of curvature plays an important role in the contact force due to impacts on the inner or outer surface of the panel, introducing one more parameter in the reconstruction problem.
Salmanpour MS, Sharif Khodaei Z, Aliabadi MH, 2015, A reference free method for damage detection and location based on geometric similarity, Pages: 133-142
This paper outlines a method exploiting geometrically similar areas as mutual baselines. The proposed method eliminates the need for previously recorded baseline sets and the pitfalls of changing environmental conditions between recording of signals. Through the use of instantaneously recorded baselines at the same time as the current interrogation signal and transducer calibration, it is possible to accurately predict the location of damage. The proposed transducer calibrated instantaneous baseline (TCIB) method was first applied to numerically simulated results. It was then validated experimentally for two different locations of artificial damage.
Pineda-Leon E, Rodriguez-Castellanos A, Basaldua-Sanchez JE, et al., 2015, Plastic, viscoplastic and creep fracture problems with the boundary element method, FATIGUE & FRACTURE OF ENGINEERING MATERIALS & STRUCTURES, Vol: 38, Pages: 40-55, ISSN: 8756-758X
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- Citations: 2
Bacarreza O, Wen P, Aliabadi MH, 2015, MICROMECHANICAL MODELLING OF TEXTILE COMPOSITES, WOVEN COMPOSITES, Vol: 6, Pages: 1-74
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- Citations: 9
Sharif-Khodaei Z, Thiene M, Aliabadi MH, 2015, Structural Health Monitoring Platform for Sensorised Composite Structures, 10th International Workshop on Structural Health Monitoring (IWSHM), Publisher: DESTECH PUBLICATIONS, INC, Pages: 1981-1987
Huang X, Aliabadi MH, Khodaei ZS, 2014, Fatigue Crack Growth Reliability Analysis by Stochastic Boundary Element Method, CMES-COMPUTER MODELING IN ENGINEERING & SCIENCES, Vol: 102, Pages: 291-330, ISSN: 1526-1492
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- Citations: 6
Rodriguez-Tembleque L, Aliabadi MH, 2014, Friction and Wear Modelling in Fiber-Reinforced Composites, CMES-COMPUTER MODELING IN ENGINEERING & SCIENCES, Vol: 102, Pages: 183-210, ISSN: 1526-1492
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- Citations: 8
Thiene M, Ghajari M, Galvanetto U, et al., 2014, Effects of the transfer function evaluation on the impact force reconstruction with application to composite panels, Composite Structures, Vol: 114, Pages: 1-9, ISSN: 0263-8223
The determination of a reliable transfer function for force reconstruction of impacts on composite panels is addressed in the paper. The reconstruction of the impact force history requires the knowledge of the transfer function which relates the response to the contact force. In this paper, a new method to determine the transfer function of a composite plate, instrumented with surface bonded piezoelectric sensors, is proposed. Impact tests are carried out and the data are used to evaluate the transfer function. The force reconstruction results, obtained by using the new transfer function, are compared with the results obtained with the classic approach. Significant improvements are observed in predicting the force history, particularly when large deflections are present; these are quantifiable as an out of plane displacement of the same order of magnitude as the thickness of the plate. The influence of increasing the impact velocity, with the related increase in the contact force, is also studied. The proposed method provides good results over a range of impact velocities. Multiple impacts were also investigated and the method could correctly reconstruct force histories of consecutive impacts.
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