374 results found
Li J, Khodaei ZS, Aliabadi MH, 2020, Dynamic fracture analysis of plates loaded in tension and bending using the dual boundary element method, Pages: 440-445, ISSN: 1013-9826
© 2020 Trans Tech Publications Ltd, Switzerland. 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.
Yue N, Aliabadi MH, 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, 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.
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.
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, 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, Advances in Boundary Element and Meshless Techniques XIX, International Conference on Boundary Element and Meshless Techniques, 2018
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, Pages: 354-357
© 2019 IEEE. A broadband energy harvester using bi-stability and frequency up-conversion is introduced for the first time in a host-parasite shape inspired by the parasitic relationship in plants. A macro-buckled hosting beam is used to create bi-stability by compressing the beam in the axial direction; two piezoelectric micro-beams are amounted on the host beam as parasitic structures to absorb the low-frequency macro-beam kinetic energy and convert it to micro-beams' high-frequency vibration at resonance. The design and operational principle are presented; a prototype was then fabricated and tested. The results illustrate the harvester is capable of harvesting low-amplitude vibration energy over a wide bandwidth at low frequencies. This design provides a potential solution for power supply in self-powered sensing applications in the Internet of Things.
Morse L, Sharif Khodaei Z, Aliabadi MH, A Dual Boundary Element based Implicit Diﬀerentiation Method for Determining Stress Intensity Factor Sensitivities for Plate Bending Problems, Engineering Analysis with Boundary Elements, ISSN: 0955-7997
Morse L, Sharif Khodaei Z, Aliabadi MH, A dual boundary element based implicit diﬀerentiation method for determining stress intensity factor sensitivities for plate bending problems, Engineering Analysis with Boundary Elements, 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.
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.
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.
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
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.
Li J, Khodaei ZS, Aliabadi MH, 2018, Dynamic dual boundary element analyses for cracked Mindlin plates, International Journal of Solids and Structures, Vol: 152-153, Pages: 248-260, ISSN: 0020-7683
In this paper, a new dual boundary element formulation is presented for dynamic crack problems in Mindlin plates. The displacement and traction boundary integral equations are derived in the Laplace frequency domain to allow for a boundary-only formulation. The cracked plate is modelled with the dual boundary element method and dynamic plate bending stress intensity factors are evaluated. Four benchmark examples are presented including mode I and mixed mode deformation. Such stress intensity factors obtained are shown to be in excellent agreement with finite element results as well as published results.
Fu H, Hami Seno A, Sharif Khodaei Z, et al., 2018, Design of a wireless passive sensing system for impact detection of aerospace composite structures, 2018 5th IEEE International Workshop on Metrology for AeroSpace (MetroAeroSpace), Publisher: IEEE, Pages: 585-589, ISSN: 2575-7490
In this paper, the design and implementation of a novel on-board wireless passive sensing system for impact detection of composite airframe is presented for the first time. Several modules, including filtering, impact detection, local processing and wireless transmission are designed and evaluated for detecting rare, random and transitory impact events. An event-triggered mechanism with high responsiveness is adopted to reduce the system power dissipation and to maintain the detection effectiveness. This design allows the system to be adaptive, energy-efficient and highly responsive to impacts. The whole system was implemented in an experimental study, and the effectiveness was evaluated and illustrated. The system was woken up by impact events in around 12 µs, and the impact data were recorded at 200 kHz (up to 5.33 MHz). This work provides a guideline for low-power, high-responsiveness passive on-board sensing system design. This system can also be adapted to other sensing applications in aerospace engineering.
Geraci G, Aliabadi MH, 2018, Micromechanical modelling of cohesive thermoelastic cracking in orthotropic polycrystalline materials, Computer Methods in Applied Mechanics and Engineering, Vol: 339, Pages: 567-590, ISSN: 0045-7825
In this paper a new micromechanical formulation is proposed for modelling thermoelastic intergranular and transgranular damage and microcracking evolution in brittle polycrystalline materials. Polycrystalline microstructures are created through a Voronoi tessellation algorithm. Each crystal has an elastic orthotropic behaviour. Damage evolution along (inter- or trans-granular) interfaces is modelled using thermo-mechanical cohesive laws and, upon failure, non-linear frictional contact analysis is introduced to model separation, stick or slip. Numerical simulations are presented either to demonstrate the validity and study the physical implications of the proposed thermoelastic formulation, in comparison with other numerical methods as well as experimental observations and literature results.
Morse L, Sharif-Khodaei Z, Aliabadi MH, 2018, Statistical inference of the equivalent initial flaw size distribution using the boundary element method under multiple sources of uncertainty, 17th International Conference on Fracture and Damage Mechanics (FDM'18), Publisher: Trans Tech Publications, Pages: 613-618, ISSN: 1013-9826
In this work, a method for determining the Equivalent Initial Flaw Size (EIFS) distribution using the Boundary Element Method (BEM) is proposed. Maximum Likelihood Estimation (MLE) is used to infer the EIFS distribution of a cracked stiffened panel under multiple sources of uncertainty, including uncertainty in the loading conditions, fatigue crack growth model parameters, and in the measurement of crack size found from routine inspections. Results suggest that MLE is an effective tool for estimating the parameters of an EIFS distribution when no prior knowledge is available regarding the EIFS distribution or its parameters.
Bekas DG, Khodaei ZS, Aliabadi MH, 2018, Structural health monitoring of scarfed repaired composite panels using inject-printed patterns, Key Engineering Materials, Vol: 774 KEM, Pages: 235-240, ISSN: 1013-9826
© 2018 Trans Tech Publications, Switzerland. A novel strategy is proposed for monitoring of bonded composite repair patch is developed and tested. A specially designed pattern was inject-printed onto the step-sanded repair surface providing real time information about the bondline structural integrity. The obtained results indicated that the proposed methodology was able to detect damage induced by an impact event. Infrared thermography (IrT) and ultrasound inspection were also employed in order to validate the proposed methodology.
Bekas D, Sharif Khodaei Z, Aliabadi MHF, 2018, An innovative diagnostic film for structural health monitoring of metallic and composite structures, Sensors, Vol: 18, ISSN: 1424-2818
A novel lightweight diagnostic film with sensors/actuators and a multiple-path wiring option using inkjet printing was developed. The diagnostic film allows for systematic, accurate, and repeatable sensor placement. Furthermore, the film is highly flexible and adaptable for placement on complex configurations. The film can be attached to the surface of the structure through a uniform secondary boundary procedure or embedded within the composite layup during curing. The surface-mounted film can simply be peeled off for repair or replacement without scratching or damaging the part. The film offers significant weight reduction compared to other available technologies. A set of extreme temperature, altitude, and vibration environment test profiles were carried out following the Radio Technical Commission for Aeronautics (RTCA) DO-160 document to assess the durability and performance of the diagnostic film for onboard application. The diagnostic film was shown to be durable and reliable in withstanding the variable operational and harsh environmental conditions of tests representing the conditions of regional aircraft
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