380 results found
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.
Chen YH, Aliabadi MH, 2020, Meshfree-based micromechanical modelling of twill woven composites, Composites Part B: Engineering, Vol: 197, Pages: 1-13, ISSN: 0961-9526
This paper presents a novel, meshfree-based micromechanical model for homogenising the elastic properties and analysing the deformation and microscopic strains/stresses of twill woven composites. The proposed model was based on a minimum unit cell (mUC) whose internal features such as the cross-sectional shape and waviness of yarns were described by using sophisticated functions. The boundary conditions imposed on the mUC were derived by applying an equivalence approach, which converts the standard form of periodic boundary conditions into a generic set of fixed and relative displacement constraints. Theoretical formulations were developed to implement the micromechanical model within the framework of the moving kriging (MK)-based element-free Galerkin (EFG) method. An in-house computer program implementing the proposed model was developed for analysing a typical twill woven composite. Good agreements were found between the meshfree-based predictions and the reference results, highlighting the proposed model capable of homogenising twill woven composites and meanwhile avoiding the commonly required pre-processing tasks such as building an explicit geometry model and generating identical meshes on the mapping surfaces to enforce boundary conditions. Three case studies were also performed to identify the sensitivities of the predicted results to three numerical parameters, i.e. the total number of field nodes, the total number of background cells, and the support domain scaling factor. The results of these studies suggest that the numbers of field nodes and background cells used must be sufficiently large, while the support domain scaling factor in an appropriate range (e.g. 2.0−3.25) to achieve convergent results.
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.
Yue N, Aliabadi MH, 2020, A scalable data-driven approach to temperature baseline reconstruction for guided wave structural health monitoring of anisotropic carbon-fibre-reinforced polymer structures, Structural Health Monitoring, Vol: 19, Pages: 1487-1506, ISSN: 1475-9217
To account for the temperature effect on guided wave signals in complex structures, a significant amount of baseline measurements typically need to be collected over a large temperature range to serve as a library of signals at all possible temperatures, which, if not impossible, is highly impractical. This article presents a data-driven temperature baseline reconstruction approach that is applicable for various structures made from the same material. The influence of temperature on the amplitude and phase of guided wave measurements are experimentally quantified as dimensionless compensation factors. The derived compensation factors are used to reconstruct baselines at various temperatures for guided wave measurements in a simple flat plate and a stiffened panel. With a single baseline measurement at 20°C and the reconstructed baseline using the predetermined temperature compensation factors, impact damage was successfully detected and located when current measurements were up to 25°C and 20°C higher than the baseline temperature, respectively.
Yue N, Aliabadi MH, 2020, Hierarchical approach for uncertainty quantification and reliability assessment of guided wave-based structural health monitoring, Structural Health Monitoring: an international journal, ISSN: 1475-9217
In this article, a hierarchical approach is proposed for the design and assessment of a guided wave-based structural health monitoring system for the detection and localisation of barely visible impact damage in composite airframe structures. The hierarchical approach provides a systemic and practical way to establish guided wave-based structural health monitoring systems for different structures in the presence of uncertainties and to quantify system performance. The proposed approach is carried out in four steps: (1) determine optimal sensor placement for the target structure and its plausible impact scenarios, (2) set detection threshold for global damage index based on the noise level present in the required environmental and operations conditions, (3) detect damage in critical locations and quantify detection performance by calculating the probability of detection, probability of false alarm and detection accuracy and (4) locate the detected damage while also quantifying the accuracy of location estimation and the probability of correctly indicating if the damage is in an area critical to the integrity of the structure. The proposed approach is demonstrated in aircraft carbon fibre-reinforced polymer structures from coupon level (simple flat panels) to sub-component level (large flat panel with multiple carbon fibre-reinforced polymer stringers and aluminium frames) for the detection and localisation of barely visible impact damage.
Feng T, Dimitrios B, Aliabadi MHF, 2020, Active health monitoring of thick composite structures by embedded and surface-mounted piezo diagnostic layer, Sensors, Vol: 20, ISSN: 1424-8220
An effective approach for an embedded piezo diagnostic layer into thick composite material is presented. The effectiveness of the approach is assessed in comparison to the surface-mounted layer. The proposed manufacturing alleviates difficulties associated with trimming edges of composites when embedding wires. The Electro-Mechanical Impedance technique is used to access the integrity of the piezoelectric sensors bonding process. Comparisons of ultrasonic guided waves are made between embedded and surface-mounted diagnostic layers and their penetration through and across the thickness of the composites. Temperature influences with the range from −40 °C up to 80 °C on embedded and surface-mounted guided waves are investigated. An investigation is carried out into the relationship between amplitude and time-of-flight with temperature at different excitation frequencies. The temperature has significant but different effects on amplitude and phase-shift of guided waves for the embedded layer compared to the surface-mounted layer. A Laser Doppler Vibrometer is used to identify the blue tack and impact damage. Both embedded and surface-mounted layers are shown to be an effective means of generating detectable wave scatter from damage.
Yoo K, Bacarreza O, Aliabadi MHF, 2020, A novel multi-fidelity modelling-based framework for reliability-based design optimisation of composite structures, Engineering with Computers: an international journal for simulation-based engineering, Pages: 1-14, ISSN: 0177-0667
A new multi-fidelity modelling-based probabilistic optimisation framework for composite structures is presented in this paper. The multi-fidelity formulation developed herein significantly reduces the required computational time, allowing for more design variables to be considered early in the design stage. Multi-fidelity models are created by the use of finite element models, surrogate models and response correction surfaces. The accuracy and computational efficiency of the proposed optimisation methodology are demonstrated in two engineering examples of composite structures: a reliability analysis, and a reliability-based design optimisation. In these two benchmark examples, each random design variable is assigned an expected level of uncertainty. Monte Carlo Simulation (MCS), the First-Order Reliability Method (FORM) and the Second-Order Reliability Method (SORM) are used within the multi-fidelity framework to calculate the probability of failure. The reliability optimisation is a multi-objective problem that finds the optimal front, which provides both the maximum linear buckling load and minimum mass. The results show that multi-fidelity models provide high levels of accuracy while reducing computation time drastically.
Farokhi H, Bacarreza O, Aliabadi MHF, 2020, Probabilistic optimisation of mono-stringer composite stiffened panels in post-buckling regime, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, Vol: 62, Pages: 1395-1417, ISSN: 1615-147X
In this paper, a multi-objective probabilistic design optimisation approach is presented for reliability and robustness analysis of composite structures and demonstrated on a mono-omega-stringer stiffened panel. The proposed approach utilises a global surrogate model of the composite structure while accounting for uncertainties in material properties as well as geometry. Unlike the multi-level optimisation approach which freezes some parameters at each level, the proposed approach allows for all parameters to change at the same time and hence ensures global optimum solutions in the given parameter design space (for both probabilistic and deterministic optimisations) within a certain degree of accuracy. The proposed approach is used in this study to conduct extensive multi-objective probabilistic and deterministic optimisations (without considering safety factors) on a mono-stringer stiffened panel. In particular, a global surrogate model is developed utilising the computational power of a high-performance computing facility. The inputs of the surrogate model are the omega-stringer geometry and the mechanical properties of the composite material, while the outputs are the fundamental linear buckling load (LBL) and the nonlinear post-buckling strength (NPS). LBL and NPS are obtained via detailed parametric finite element models of the mono-stringer stiffened panel; in the nonlinear model, the interface between the skin and the omega-stringer is modelled via cohesive elements to allow for debonding in the post-buckled regime. Extensive multi-objective optimisations are conducted on the surrogate model using deterministic and probabilistic approaches to examine the omega-stringer geometric parameters mostly affecting the system robustness and reliability. The differences between deterministic and probabilistic designs are highlighted as well.
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.
Li L, Aliabadi MH, 2019, Elastic property prediction and damage mechanics analysis of 3D braided composite, THEORETICAL AND APPLIED FRACTURE MECHANICS, Vol: 104, ISSN: 0167-8442
Chen YH, Aliabadi MH, 2019, Micromechanical modelling of the overall response of plain woven polymer matrix composites, International Journal of Engineering Science, Vol: 145, Pages: 1-18, ISSN: 0020-7225
This paper presents a novel approach to micromechanical modelling of plain woven polymer matrix composites and predicting the overall response including the nonlinear and rate-dependent behaviour. The nonlinearity and rate-dependence of plain woven composites is evaluated by describing the behaviour of the polyer matrix using a viscoplastic model. The damage evolution of the yarn material and deformation of the woven fabric are investigated by considering Weibull distribution based formulations and a shear-modulus discount approach, respectively. The explicit meshfree method with time-dependent periodic boundary conditions for unit cell (UC) models that describe the internal architecture of plain woven composites is presented for the first time. For validation, numerical examples are performed to simulate the EP121-C15-53 plain woven composite subjected to in-plane normal/off-axis tensile loading conditions and at three different strain rates, i.e. 10−1 s−1, 10−3 s−1 and 10−5 s−1. Good agrements are found between the numerical and experimental results, with both the quasi-linear, rate-insensitive behaviour in the normal direction and the nonlinear, rate-dependent response in the off-axis direction successfully predicted.
Bekas DG, Mendias MM, Sharif Khodaei Z, et 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).
Bekas DG, Saenz-Castillo D, Sharif Khodaei Z, et 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.
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.
Morse L, Sharif Khodaei Z, Aliabadi MH, 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.
Seno AH, Aliabadi MHF, 2019, Impact localisation in composite plates of different stiffness impactors under simulated environmental and operational conditions, Sensors (Basel, Switzerland), Vol: 19, ISSN: 1424-8220
A parametric investigation of the effect of impactor stiffness as well as environmental and operational conditions on impact contact behaviour and the subsequently generated lamb waves in composite structures is presented. It is shown that differing impactor stiffness generates the most significant changes in contact area and lamb wave characteristics (waveform, frequency, and amplitude). A novel impact localisation method was developed based on the above observations that allows for variations due to differences in impactor stiffness based on modifications of the reference database method and the Akaike Information Criterion (AIC) time of arrival (ToA) picker. The proposed method was compared against a benchmark method based on artificial neural networks (ANNS) and the normalised smoothed envelope threshold (NSET) ToA extraction method. The results indicate that the proposed method had comparable accuracy to the benchmark method for hard impacts under various environmental and operational conditions when trained only using a single hard impact case. However, when tested with soft impacts, the benchmark method had very low accuracy, whilst the proposed method was able to maintain its accuracy at an acceptable level. Thus, the proposed method is capable of detecting the location of impacts of varying stiffness under various environmental and operational conditions using data from only a single impact case, which brings it closer to the application of data driven impact detection systems in real life structures.
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.
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.
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.
Benedetti I, Milazzo A, Aliabadi MHF, 2019, Advances in Boundary Element and Meshless Techniques XX, International Conference on Boundary Element and Meshless Techniques
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.
Garcia-Sanchez F, L Rodriguez-Tembleque L, Aliabadi MH, 2019, Advances in Boundary Element and Meshless Techniques XIX, International Conference on Boundary Element and Meshless Techniques, 2018
Li J, Khodaei ZS, Aliabadi MH, 2019, Modelling of the high-frequency fundamental symmetric Lamb wave using a new boundary element formulation, International Journal of Mechanical Sciences, Vol: 155, Pages: 235-247, ISSN: 0020-7403
This paper presents a new boundary element formulation for modelling the fundamental symmetric Lamb wave (S0 mode) propagating in the high frequency range. At such high frequencies, the S0 mode reveals significant dispersive character. Conventional BEM formulations governed by the generalised plane stress theory fail to accurately represent the dispersive properties of the S0 mode and to handle out-of-plane loads because the effects of thickness-stretch are not considered. Therefore, a new BEM formulation is proposed based on the dynamic fundamental solutions which are derived for the first time for a higher-order plate theory (Kane–Mindlin) taking into account coupling between extensional motion and the first mode of thickness vibration. Only plate edges are required to be discretized using simple line elements in the proposed BEM formulation. Three benchmark examples are presented where the solutions from the new BEM formulation are shown to be in excellent agreement with analytical and three-dimensional finite element results. Furthermore, the advantage of the proposed formulation is demonstrated through comparisons with the BEM results based on the generalised plane stress theory.
Fu H, Sharif Khodaei Z, Aliabadi M, 2019, A bio-inspired host-parasite structure for broadband vibration energy harvesting from low-frequency random sources, Applied Physics Letters, Vol: 114, ISSN: 0003-6951
Energy harvesting for low-power sensing has drawn great attention, but still faces challenges in harnessing broadband random motions. Inspired by the parasitic relationship in plants, a host-parasite vibration harvester is designed to scavenge random low-frequency vibrations by incorporating bi-stability and frequency up-conversion within such a design. A hosting beam is formed in a buckled condition by clamping it at both ends and applying an axial compression load. Two parasitic piezoelectric beams are fixed at the center of the hosting beam and plucked at the free ends by two plectra on the hosting beam, while it oscillates in an inter-well mode. The low-frequency hosting beam oscillation is converted to high-frequency parasitic beam's vibration at resonance due to the plucking effect, allowing the harvester to convert the broadband low-frequency motion into electricity effectively. The electromechanical dynamics are modeled and the design is validated experimentally. The harvester is capable of harnessing low-frequency random vibration (0.0018 g2/Hz @ 5–400 Hz) over a wide bandwidth. More than 1 mJ energy was collected over 100 s under this pseudorandom vibration.Energy harvesting has been recognized as one of the key enablers for self-powered sensing applications in the era of Internet of things.1–4 However, enhancing the energy harvesting effectiveness requires significant efforts, especially for different energy sources under various conditions, such as low-frequency human motion,5,6 random aircraft vibrations7 or ocean waves.8 Harnessing a random, broadband and low-frequency kinetic energy is one of the key challenges, and different mechanisms have been developed to enhance the conversion performance.Nonlinear dynamics are one major consideration to enhance the operation bandwidth.9–11 Different harvesters have been developed with monostable,12–14 bistable15–17 and multistable behaviors.18–20 The aim is to al
Fu H, Sharif Khodaei Z, Aliabadi MH, 2019, An energy eﬃcient wireless module for on-board aircraft impact detection, Nondestructive Characterization and Monitoring of Advanced Materials, Aerospace, Civil Infrastructure, and Transportation XIII, Publisher: Society of Photo-optical Instrumentation Engineers, ISSN: 0277-786X
An innovative wireless passive system for impact detection on large-scale composite airframe structures is presented. The wireless system is designed to operate with a sensor network for onboard of aircraft for structural health monitoring, of composite airframe. The wireless systems efficient design allows for low power consumption, wireless communication capability, system robustness and large sensing area. The system is evaluated on a large-scale stiffened composite fuselage under different operational conditions. It is demonstrated that it is possible to detect impact events with different impact energy levels and impact locations over a large monitoring area. This work provides a potential solution for aircraft on-board structural health monitoring with no human intervention. This sensing system can be also adapted to other Internet of Things and structural health monitoring applications.
Geraci G, Aliabadi MH, 2019, Micromechanical modeling of cohesive thermoelastic steady‐state and transient cracking in polycrystalline materials, International Journal for Numerical Methods in Engineering, Vol: 117, Pages: 1205-1233, ISSN: 0029-5981
In this paper, a micromechanical formulation is proposed for modeling thermoelastic intergranular and transgranular damage and microcracking evolution in brittle polycrystalline materials. The model is based on a multiregion boundary element approach combined with the dual boundary element formulation. Polycrystalline microstructures are created through a Voronoi tessellation algorithm. Each crystal has an elastic isotropic behavior, and multiphase aggregates have been considered. Damage evolution along (intergranular or transgranular) interfaces is modeled using thermomechanical cohesive laws, and upon failure, nonlinear frictional contact analysis is introduced to model separation, stick or slip. Steady‐state and transient thermoelastic formulations have been modeled, and numerical simulations are presented, not only to demonstrate the validity but also to study the physical implications of the proposed formulation, in comparison with other numerical methods as well as experimental observations and literature results.
Morse L, Sharif Khodaei Z, Aliabadi MH, 2019, A multi-fidelity modelling approach to the statistical inference of the equivalent initial flaw size distribution for multiple-site damage, International Journal of Fatigue, Vol: 120, Pages: 329-341, ISSN: 0142-1123
Abstract:A new methodology for the statistical inference of the Equivalent Initial Flaw Size distribution (EIFSD) using the Dual Boundary Element Method (DBEM) is proposed. As part of the inference, Bayesian updating is used to calibrate the EIFS based on data obtained from simulated routine inspections of a structural component from a fleet of aircraft. An incremental crack growth procedure making use of the DBEM is employed for the modelling of the simultaneous growth of cracks in the structure due to fatigue. Multi-fidelity modelling, in the form of Co-Kriging, is used to create surrogate models that act in place of the DBEM model for the expensive Monte Carlo sampling procedure required for the statistical inference of the EIFSD. The proposed methodology is applied to a numerical example featuring a long fuselage lap joint splice in presence of multiple site damage (MSD). Results show that the EIFSD can be accurately estimated with data from 50 inspections. The employed Co-Kriging models proved to be effective substitutes for the DBEM model, providing significant reductions in the computational cost associated with the implementation of the proposed statistical inference methodology.Abbreviations:EIFSD Equivalent Initial Flaw Size Distribution, MSD Multiple Site Damage, DBEM Dual Boundary Element Method
Bekas DG, Sharif-Khodaei Z, Baltzis D, et al., 2019, Quality assessment and damage detection in nanomodified adhesively-bonded composite joints using inkjet-printed interdigital sensors, Composite Structures, Vol: 211, Pages: 557-563, ISSN: 0263-8223
In this work, the development of a planar interdigital capacitive sensor, directly onto the surface of a composite, for determining the initial quality of curing of bonded composite joints and assessing their long-term durability is presented. The sensor consisted of an interlocking comb-shaped array of silver electrodes and used to monitor the progress of cure of an adhesive resin and the subsequent damage state of the bond line in adhesively-bonded composite joints using impedance spectroscopy. The obtained results from the mechanical characterization indicated that the developed sensor did not affect the quality of the bondline while the added weight of the sensor is negligible. The curing process of the adhesive epoxy was successfully monitored while the ability of the sensor to assess the developed damage created by the mechanical loading was confirmed using transient infrared thermography.
Fu H, Sharif Khodaei Z, Aliabadi MH, 2019, An event-triggered energy-efficient wireless structural health monitoring system for impact detection in composite airframes, IEEE Internet of Things Journal, Vol: 6, Pages: 1183-1192, ISSN: 2327-4662
In this paper, a low-power high-response wireless structural health monitoring system (WSHMS) is designed, implemented and experimentally evaluated for impact detection in composite airframes. Due to the rare, random and transitory nature of impacts, an event-triggered mechanism is adopted for allowing the system to exhibit low power consumption when no impact occurs and high performance when triggered. System responsiveness, robustness and energy efficiency are considered and modelled. Based on system requirements and functions, several modules are designed, including filtering, impact detecting, local processing and wireless communicating modules. The system was implemented on a printed circuit board. The response time is about 12 us with an average current lower than 1 mA when the impact activity is lower than 0.1%. The system exhibits high robustness to ambient vibration noises and is also capable of accurately and responsively capturing multiple sensing input channels (up to 24 channels). This work presents a low-latency energy-aware WSHMS for impact detection of composite structures. It can be adapted to monitor of other rare, random and ephemeral events in many Internet of Things applications.
Fu H, Khodaei ZS, Aliabadi MHF, 2019, BROADBAND ENERGY HARVESTING USING BI-STABILITY AND FREQUENCY UP-CONVERSION FOR SELF-POWERED SENSING IN INTERNET OF THINGS, 20th International Conference on Solid-State Sensors, Actuators and Microsystems and Eurosensors XXXIII (TRANSDUCERS and EUROSENSORS), Publisher: IEEE, Pages: 354-357
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