401 results found
Giannakeas IN, Khodaei ZS, Aliabadi MH, 2023, Model Assisted Probability of Detection Using a Digital Clone Platform for Composite Structures, 10th European Workshop on Structural Health Monitoring (EWSHM), Publisher: SPRINGER-VERLAG SINGAPORE PTE LTD, Pages: 679-688, ISSN: 2366-2557
Feng T, Sharif Khodaei Z, Aliabadi MHF, 2022, Influence of composite thickness on ultrasonic guided wave propagation for damage detection, Sensors, Vol: 22, ISSN: 1424-8220
In this paper, the propagation properties of ultrasonic guided waves (UGWs) in different-thickness composites (i.e., 2, 4 and 9 mm) were critically assessed, and their effectiveness for damage detections and localisations under varying temperatures was demonstrated. A diagnostic film with phased-array lead zirconate titanate (PZT) transducers based on the ink-jet printing technique was used in the experiments. Initially, the dispersion curves for these composites were compared. Next, the effects of the composite thickness on the A0 and S0 mode amplitudes and the group velocity were investigated by active sensing. Next, the behaviours of UGWs under varying temperatures in different-thickness plates were also investigated. Finally, surface-mounted artificial damage and impact damage were detected and located in different composites.
Aliabadi M, 2022, Deep learning approach to impact classification in sensorized panels using self-attention, Sensors, Vol: 22, Pages: 1-17, ISSN: 1424-8220
This paper proposes a new method of impact classification for a Structural Health Monitoring system through the use of Self-Attention, the central building block of the Transformer neural network. As a topical and highly promising neural network architecture, the Transformer has the potential to greatly improve the speed and robustness of impact detection. This paper investigates the suitability of this new network, confronting the advantages and disadvantages offered by the Transformer and a well-known and established neural network for impact detection, the Convolutional Neural Network (CNN). The comparison is undertaken on performance, scalability, and computational time. The inputs to the networks were created using a data transformation technique, which transforms the raw time series data collected from the network of piezoelectric sensors, installed on a composite panel, through the use of Fourier Transform. It is demonstrated that the Transformer method reduces the computational complexity of the impact detection significantly, while achieving excellent prediction results.
Morse L, Mallardo V, Aliabadi FMH, 2022, Manufacturing cost and reliability-based shape optimization of plate structures, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Vol: 123, Pages: 2189-2213, ISSN: 0029-5981
Feng T, Aliabadi MHF, 2022, Smart patch for structural health monitoring of composite repair, Applied Sciences, Vol: 12, ISSN: 2076-3417
The bondline integrity of a repair patch to the parent composite laminate is considered the most important factor in the repair design. A smart repair patch is proposed here to allow for real-time ultrasonic guided wave monitoring of repaired composites. A diagnostic film with lead zirconate titanate (PZT) transducers and inkjet-printed wires is embedded into the repair patch using a cut-out method. The electro-mechanical impedance (EMI) method is used to verify the integrity of the embedded PZT transducers. The performance of the smart repair patch is assessed on the external panel with artificial bondline delamination and surface-mounted artificial damage. The damage index correlation coefficient and delay-and-sum (DAS) algorithm are used for damage detection and localization. The results show that the developed repair patch can successfully detect and locate damages.
Zhuang M, Morse L, Khodaei ZS, et al., 2022, Statistical inference of the Equivalent Initial Flaw Size Distribution for an anisotropic material with the Dual Boundary Element Method, INTERNATIONAL JOURNAL OF FATIGUE, Vol: 158, ISSN: 0142-1123
Seno AH, Aliabadi MHF, 2022, Uncertainty quantification for impact location and force estimation in composite structures, STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL, Vol: 21, Pages: 1061-1075, ISSN: 1475-9217
Rodriguez-Tembleque L, Sanz-Herrera JA, Aliabadi MH, 2022, Preface, JOURNAL OF MULTISCALE MODELLING, Vol: 13, ISSN: 1756-9737
Giannakeas I, Sharif Khodaei Z, Aliabadi MH, 2022, Structural health monitoring cost estimation of piezo-sensorized aircraft fuselage, Sensors, Vol: 22, Pages: 1-21, ISSN: 1424-8220
Guided waves-based SHM systems are of interest in the aeronautic sector due to their lightweight, long interrogation distances, and low power consumption. In this study, a bottom-up framework for the estimation of the initial investment cost (COTC) and the added weight (WAW) associated with the integration of a SHM system to an aircraft is presented. The framework provides a detailed breakdown of the activities and their costs for the sensorization of a structure using a fully wired approach or the adoption of the printed diagnostic film. Additionally, the framework considers the difference between configuring the system for Manual or Remote data acquisition. Based on the case study presented on the sensorization of a regional aircraft composite fuselage, there is a trade-off between COTC and WAW for the SHM options considered. The Wired–Manual case leads to the lowest COTC with the highest WAW, while the combination of diagnostic film with a Remote system leads to the highest COTC and the lowest WAW. These estimations capture the characteristics of each system and can be integrated into cost–benefit analyses for the final selection of a particular configuration.
Yoo K, Bacarreza O, Aliabadi MHF, 2022, 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, Vol: 38, Pages: 595-608, 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.
Giannakeas IN, Khodaei ZS, Aliabadi MH, 2022, Digital clone testing platform for the assessment of SHM systems under uncertainty, Mechanical Systems and Signal Processing, Vol: 163, Pages: 1-20, ISSN: 0888-3270
The performance of a Structural Health Monitoring (SHM) system can be assessed using Probability of Detection (PoD) curves, which is a common tool for the evaluation of Non-Destructive Testing (NDT) methods. This study presents a novel digital clone platform to quantify and account for uncertainties that can be detrimental to the reliability of a SHM system. Uncertainties relating to experimental measurement noise and Environmental and Operational Conditions (EOC) are considered during the definition of a threshold value that aims at reliably distinguishing between pristine and damaged signals. At the same time, the variability of impact damage characteristics and uncertainties associated with Lamb waves interaction in composites are captured though the Bayesian calibration of a Finite Element (FE) model using experimental observations. The FE model is integrated within the digital clone testing platform to substitute the experimental testing and generate a statistical sample of distributed impact events at different locations on a composite plate and compute the Model Assisted Probability of Detection (MAPOD). This approach allows the estimation of the system’s performance under different EOC that can be used during the selection and operation of a specific SHM configuration.
Yoo K, Bacarreza Nogales O, Aliabadi MHF, 2021, Multi-fidelity probabilistic optimisation of composite structures under thermomechanical loading using gaussian processes, Computers and Structures, Vol: 257, Pages: 1-14, ISSN: 0045-7949
A multi-fidelity probabilistic optimisation method for the design of composite structures subjected tothermomechanical loading isintroduced in this work for the first time. The proposed multi-fidelity approach offersconsiderable computation efficiency as well as sufficient accuracy, enabling probabilistic optimisation to includemore design variables in the early design phase. This approach incorporates both nonlinear information fusionalgorithms and multi-level optimisation to achieve increased accuracy and computation time savings. In thisoptimisation process, a High-Fidelity Model (HFM) covers only a part of the entire design space with informationcollected uniformly while providing high-fidelity information of other design spaces sparsely without causingextra computational cost. Simultaneously, a Low-Fidelity Model (LFM) explores the whole design space tocompensate lack of high-fidelity information. In this manner, the number of high-fidelity information to constructa multi-fidelity model is dramatically reduced. The Reliability-Based Design Optimisation (RBDO) demonstratedthe proposed multi-fidelity method of a mono-stringer stiffened composite panel under thermomechanical loadingusing Gaussian Processes (GPs)
Feng T, M H Ferri A, 2021, Structural integrity assessment of composites plates with embedded PZT transducers for structural health monitoring, Materials, Vol: 14, ISSN: 1996-1944
Active sensing using ultrasonic guided waves (UGW) is widely investigated for monitoring possible damages in composite structures. Recently, a novel diagnosed film based on a circuit-printed technique with piezoelectric lead zirconate titanate (PZT) transducers has been developed. The diagnostic film is a replacement for the traditional cable connection to PZT sensors and has been shown to significantly reduce the weight of the host structure. In this work, the diagnosed films were embedded into composite structures during manufacturing using a novel edge cut-out method during lay-up, which allowed for edge trimming after curing. In this paper, the effect of fatigue loading on the integrity of PZT transducers is initially investigated. The electro-mechanical impedance (EMI) properties at different fatigue loading cycles were used as the diagnostic measure for the performance of the sensors. At the same time, the behaviours of UGW were investigated at different fatigue loading cycles. It was found that the EMI properties and active sensing behaviours remained stable up to 1 million cycles for the force ranges of 0.5~5 kN and 1~10 kN. Next, the effect of embedding the diagnosed film on the mechanical properties of the host composite structure was investigated. Tensile and compressive tests were conducted and the elastic modulus of composite coupons with and without embedded PZT diagnosed films were compared. The elastic modulus of composite coupons with PZT diagnosed films embedded across the entire coupon reduced by as much as 20% for tensile tests and just over 10% for compressive tests compared to the coupons without embedded sensors. These reductions are considered the worst-case scenario, as in real structures the film would only be embedded in a relatively small area of the structure.
Yue N, Aliabadi MH, 2021, Hierarchical approach for uncertainty quantification and reliability assessment of guided wave-based structural health monitoring, Structural Health Monitoring: an international journal, Vol: 20, Pages: 2245-2893, 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.
Yue N, Khodaei ZS, Aliabadi MH, 2021, Damage detection in large composite stiffened panels based on a novel SHM building block philosophy, SMART MATERIALS AND STRUCTURES, Vol: 30, ISSN: 0964-1726
Yoo K, Bacarreza Nogales O, Aliabadi MHF, 2021, Multi-fidelity robust design optimisation for composite structures based on low-fidelity models using successive high-fidelity corrections, Composite Structures, Vol: 259, Pages: 1-12, ISSN: 0263-8223
In this paper, a novel multi-fidelity modelling-based optimisation framework is developed for the robust designof composite structures. The proposed framework provides significant savings on computation time compared toboth conventional multi-fidelity and high-fidelity modelling methods while maintaining an acceptable level ofaccuracy. Artificial neural networks (ANNs) and multi-level optimisation approach are both incorporated into thismulti-fidelity modelling formulation. The framework utilises varied High-Fidelity Model (HFM) and LowFidelity Model (LFM) covering different design spaces. This means that the HFM has only a few design variables,whereas the LFM explores the entire design spaces during the optimisation process. The proposed multi-fidelityformulation is demonstrated by the Robust Design Optimisation (RDO) of a mono-stringer stiffened compositepanel considering design uncertainty under non-linear post-buckling regime.
Morse L, Khodaei ZS, Aliabadi MH, 2020, Reliability-based fracture analysis for plate bending problems with the dual boundary element method, FRACTURE AND DAMAGE MECHANICS: Theory, Simulation and Experiment, Publisher: AIP Publishing, Pages: 1-7
A novel methodology is presented for the efficient reliability analysis of plate structures containing cracks with the Dual Boundary Element Method (DBEM). The derivatives of the DBEM plate formulations for the Crack Surface Displacement Extrapolation (CSDE) method have been derived for the first time and are used as part of an Implicit Differentiation Method (IDM) for the efficient calculation of Stress Intensity Factor (SIF) sensitivities. A numerical example is investigated in which results from the presented CSDE methodology are compared to those from the J-integral. The SIF sensitivities were used with the First-Order Reliability Method (FORM) to determine the reliability of a plate structure containing a crack. Results indicate that the proposed CSDE methodology is capable of providing estimates for reliability that are very similar to those provided by the J-integral. Given that the proposed CSDE methodology can be easier to implement, it could prove to be an effective alternative to the J-integral for the efficient reliability analysis of plate structures containing cracks.
Giannakeas IN, Sharif-Khodaei Z, Aliabadi MH, 2020, Assessment of the performance of different element types for guided wave simulations in abaqus, FRACTURE AND DAMAGE MECHANICS: Theory, Simulation and Experiment, Publisher: American Institute of Physics, Pages: 1-10, ISSN: 1551-7616
Accurate numerical tools for the simulation of wave propagation are essential for the development and optimization of guided wave based Structural Health Monitoring systems. This article aims in delivering a systematic comparison of the Finite Element simulation of Lamb wave propagation using different types of elements. The numerical simulations are all realized within the environment of the commercial software Abaqus. In total three different element types are considered: conventional shell, continuum shell and 3D solid elements. To evaluate the performance of each element type, the numerically simulated signals are compared with experimental measurements from two panels. The first panel is made of Aluminium while the second is a layered composite panel. When continuum or 3D solid elements are used, the numerical predictions are closely correlated to the experimental observations. Accurate predictions were also made using conventional shell elements to model wave propagation in the first panel however, the group velocity for the first symmetric wave mode is over-estimated for the second panel when the excitation frequency is fc = 250kHz.
Giannakeas IN, Sharif-Khodaei Z, Aliabadi MH, 2020, On the estimation of material properties using guided wave measurements for the calibration of finite element models, ISSN: 0094-243X
The design and development of robust and reliable guided wave Structural Health Monitoring systems require accurate information of the structure's material properties. This is needed by various analysis tools for the determination of wave propagation characteristics in order to evaluate and optimize the system's performance. Estimation of the mechanical properties of composite materials using Lamb wave measurements is not straightforward as it requires the solution of an inverse problem. In this study, a numerical procedure is presented for the material properties estimation. The aim is to obtain estimates of the unknown material properties using circular surface mounted piezoelectric transducers that can be used for material characterization or calibration of numerical models. The procedure utilizes the Semi-analytical finite element method for the efficient computation of the dispersion curves and a genetic algorithm for the extraction of the material properties that fit best the experimental observations.
Li J, Khodaei ZS, Aliabadi MH, 2020, Boundary element analysis of lamb wave scattering by a through-thickness crack in a plate, ISSN: 0094-243X
This paper aims to analyse Lamb-wave scattering by a through-thickness crack in a plate using the boundary element plate formulations. These formulations allow to discretize the plate boundaries including plate edges and crack surfaces using simple one-dimensional line elements. Since infinite nature of the plate can be rigorously treated using the boundary element method, truncation of the plate domain is avoided to model the infinite domain. The crack is modelled using an efficient dual boundary element method, which allows to treat the crack surfaces as extra plate boundaries. The detailed scattering process is illustrated using snapshots at different time points.
Seno AH, Aliabadi MHF, 2020, Correction: Seno, A.H.; Ferri Aliabadi, M.H. Impact Localisation in Composite Plates of Different Stiffness Impactors under Simulated Environmental and Operational Conditions. Sensors 2019, 19, 3659, Sensors (Basel, Switzerland), Vol: 20, ISSN: 1424-8220
The author wishes to make the following correction to this paper [...].
Seno AH, Aliabadi MHF, 2020, A novel method for impact force estimation in composite plates under simulated environmental and operational conditions, Smart Materials and Structures, Vol: 29, Pages: 1-16, ISSN: 0964-1726
During its lifetime, an aircraft structure is subjected to various impacts from various sources such as tool drops, hail, ground service equipment, etc. In modern composite structures, these impacts have a significant chance of generating barely visible damage (BVID) which may lead to catastrophic failure of a structure if left undetected to grow. However, BVID is difficult to detect during routine visual inspection without specialised non-destructive inspection and thus there is large interest in developing monitoring systems for estimating the location and severity of impact events. Currently, most systems and methods have been developed for controlled lab conditions and do not consider the wide range of impact parameters in real life operation (environmental conditions, vibration, impactor stiffness, angle, etc) which may severely compromise the accuracy of these methods. In this study we have explored two methods for maximum impact force estimation, deconvolution and a novel gradient method, for the purpose of reliable severity assessment in composite aircraft structures under simulated environmental and operational conditions. It is shown that both methods allow accurate and robust estimation of the maximum impact force from various cases of impacts (variation of impact energy, mass, stiffness, angle, temperature, source) using minimum initial data from a single impact case. From further testing it is demonstrated that the gradient method is robust towards the effects of impact localisation errors and noise. The gradient method also has much less computational and storage requirements and is thus more feasible to integrate with current data acquisition systems being developed for structural health monitoring. Thus, we conclude that the proposed gradient method is suitable for impact force monitoring and severity assessment in composite aircraft structures in the simulated environmental and operational conditions.
Salehzadeh Nobari AE, Aliabadi MHF, 2020, A multilevel isolation forrest and convolutional neural network algorithm for impact characterization on composite structures, Sensors, Vol: 20, Pages: 5896-5896, ISSN: 1424-8220
In this paper, a Deep Learning approach is proposed to classify impact data based on the type of impact (Hard or Soft Impacts), via obtaining voltage signals from Piezo-Electric sensors, mounted on a composite panel. The data is processed further to be classified based on their energy, location and material. Minimalistic and Automated feature extraction and selection is achieved via a deep learning algorithm. Convolutional Neural Networks (CNN) are employed to extract and select important features from the voltage data. Once features are selected the impacts, are classified based on either, Hard Impacts (simulated from steel impactors in a lab setting), Soft Impacts (simulated from silicon impactors in a lab setting) and their corresponding location and energy levels. Furthermore, in order to use the right data for training they are obtained from the signals as anomalies via Isolation Forests (IF) to speed up the process. Using this approach Hard and Soft Impacts, their corresponding locations and respective energies are identified with high accuracy.
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: an international journal, 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.
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.
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.
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