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This work investigates the linear aero-thermo-elastic flutter and buckling stability of supersonic soft core sandwich panels with variable stiffness composite skins using refined layerwise finite element models based on shear deformation theories devoid of thickness stretching, as well as quasi-3D theories with thickness stretching involving Lagrange z -expansions. The proposed numerical applications of soft core sandwich panels, with either unidirectional or curvilinear fibres, highlight that the spatially varying fibre orientations, core thickness ratio and applied thermal loads significantly influence the aero-thermo-elastic response behaviour. Additionally, it is concluded that high-order layerwise models with thickness stretching are often crucial to properly capture the complex aeroelastic behaviour of thermally loaded sandwich panels experiencing flutter due to high-order modes. Nonetheless, the layerwise first-order shear deformation model ensures a fair compromise between numerical accuracy and computational efficiency when flutter arises in the first two modes. [ABSTRACT FROM AUTHOR]

This work focuses on the active aero-visco-elastic flutter control of smart sandwich panels under supersonic airflow by combining viscoelastic materials with variable stiffness composites and surface bonded piezoelectric sensor/actuator layers, exploring variable-order layerwise models based on shear deformation theories. Numerical applications of smart sandwich panels encompass either viscoelastic or purely elastic core, along with elastic layers of composite laminates, using unidirectional or curvilinear fibres, considering thin and moderately thick panels, as well as narrow and wide cores. Proportional and derivative feedback control laws are implemented resorting to the electric potential differences across the piezoelectric layers. Comparing the control laws, it is concluded that the proportional control has a significant stabilizing effect on the occurrence of coupled-mode flutter, as in sandwich panels with purely elastic core, unlike the derivative control. However, when dealing with single mode flutter, as in viscoelastic sandwich panels described with complex modulus approach, the derivative control outperforms the proportional control in improving the flutter resistance. Ultimately, the accuracy assessment of the models predictive capabilities in active flutter control analysis reveals that although the layerwise first-order model ensures a good compromise between numerical accuracy and computational efficiency, especially in thin sandwich panels, high-order models are necessary for moderately thick panels. • Assessment of refined layerwise models for active aero-visco-elastic flutter control. • Viscoelastic and purely elastic smart sandwich panels explored. • Variable stiffness composite skins with curvilinear fibres examined. • Evaluation of proportional and derivative feedback control laws. [ABSTRACT FROM AUTHOR]

This work focuses on the layerwise finite element modelling and active aeroelastic flutter control of smart variable stiffness laminated composite panels with surface bonded piezoelectric layers/patches under supersonic airflow. The proposed aero-electro-elastic models make use of the First- and Third-order Shear Deformation Theories, along with a linear through-thickness distribution of the electric potential, whereas the effect of the supersonic airflow is described by the First-order Piston Theory. Numerical applications of simply supported smart composite panels with either curvilinear or unidirectional fibres are provided for the accuracy assessment of the proposed models predictive capabilities, considering various side-to-thickness ratios and control conditions. The effect of proportional control on the aeroelastic flutter response is discussed for both airflow along the x -axis and yawed airflow, in addition to three different placement configurations of the piezoelectric patches. [ABSTRACT FROM AUTHOR]

Abstract Three-dimensional (3D) exact hygrothermal elasticity solutions are developed to study the behaviour of simply supported rectangular multilayered composite plates, considering any combination of orthotropic and/or isotropic layers, under hygro-thermo-mechanical loadings. In agreement with the 3D exact elasticity solutions derived by Pagano in the early 1970s, the form of the through-thickness exact solutions of any given layer depends, in fact, on whether the layer material is isotropic or (at most) orthotropic. The 3D exact thermoelastic solutions found, already available, consider either only isotropic layers or only (at most) orthotropic composite layers. This work aims to be all-inclusive, in addition to a further development by considering hygrothermal elasticity. The results here presented consider composite laminates, fibre metal laminates and sandwich plates with different side-to-thickness ratios under a series of hygro-thermo-mechanical loadings. A transverse mechanical load and/or thermal load and/or hygroscopic load are imposed on the multilayered plate top and bottom surfaces to study the effects of hygrothermal environments in the multilayered plate behaviour. These effects are demonstrated by the through-thickness distributions of displacements, stresses, temperature and weight percent moisture content for the selected multilayered plates under different hygro-thermo-mechanical loadings, which may serve as 3D benchmark exact solutions. [ABSTRACT FROM AUTHOR]

Abstract This work presents a new layerwise mixed model for the fully coupled thermo-mechanical static analysis of multilayered plates with embedded functionally graded material (FGM) layers, either skins or core layers, under thermal and/or mechanical loads. This model is able to fully describe a two-constituent metal-ceramic FGM layer z -continuous effective properties through-thickness, using any given homogenization method, and is here extended to the fully coupled thermo-mechanical analysis. It is based on a mixed least-squares formulation with a layerwise variable description for displacements, transverse stresses and in-plane strains, along with temperature, transverse heat flux and in-plane components of the thermal gradient, taken as independent variables. This mixed formulation ensures that the interlaminar C 0 continuity requirements, where the material properties may actually change, are fully fulfilled a priori by all chosen independent variables. The numerical results consider single-layer and multilayered plates with different side-to-thickness ratios, under thermal or mechanical loads, using mainly Mori-Tanaka estimate for the FGM effective properties with different material gradation profiles. The results are assessed by comparison with three-dimensional (3D) exact solutions, and demonstrate the model capability to predict a highly accurate quasi-3D thermo-mechanical description of the through-thickness distributions of displacements and stresses, as well as temperature and heat flux. [ABSTRACT FROM AUTHOR]

Abstract This work presents a new layerwise mixed model for the static analysis of multilayered plates with embedded functionally graded material (FGM) layers subjected to transverse mechanical loads. This model is capable to fully describe a two-constituent metal-ceramic FGM layer continuous variation of material properties in the thickness direction, using any given homogenization method to estimate its effective properties. The present model is based on a mixed least-squares formulation with a layerwise variable description for displacements, transverse stresses and in-plane strains, chosen as independent variables. This mixed formulation ensures that the interlaminar C 0 continuity requirements at the layers interfaces, where the material properties actually change, are fully fulfilled a priori for all independent variables. The order of the in-plane two-dimensional finite element approximations and the order of the z -expansion through each layer thickness, as well as the number of layers, whether FGM layers or not, are considered free parameters. The full description of the FGM effective properties is achieved by applying to the z -continuous elastic coefficients a z -expansion through the layer thickness of a given order, set as an added free parameter, in a similar approach to finite element approximations. The numerical results consider both single-layer and multilayered functionally graded plates with different side-to-thickness ratios, using either Mori-Tanaka or the rule of mixtures estimates for the FGM effective properties with different material gradation profiles. The present model results are assessed by comparison with three-dimensional (3D) exact solutions and closed form solutions, which demonstrate its capability to predict a highly accurate quasi-3D description of the displacements and stresses distributions altogether. [ABSTRACT FROM AUTHOR]

This work provides an assessment of Equivalent Single Layer (ESL) and Layerwise finite element models, aimed for panel flutter and buckling analysis of supersonic variable stiffness composites, exploring variable-order shear deformation theories and Lagrange z -expansions. Numerical applications focus on simply supported panels with curvilinear fibre composite layers, including a cross-ply configuration for comparison purposes, and various side-to-thickness ratios. The accurate prediction of transverse shear and bending–twisting coupling is highlighted, as rather necessary for proper tailoring and analysis of supersonic curvilinear composites, especially when including in-plane loads. This is attainable through high-order ESL descriptions, in thin panels, even without thickness stretching. • Refined models for aeroelastic stability analysis of variable stiffness composites. • Variable-order ELS and LW descriptions assessed for flutter and buckling response. • Proper modelling of curvilinear fibre composites in pre-stressed supersonic panels. [ABSTRACT FROM AUTHOR]

The development of advanced finite element models suitable for analysis of smart structures depends on a comprehensive understanding of the high layerwise inhomogeneity in mechanical and electric properties present in multilayered piezoelectric composite structures. The assessment of advanced models still continues to rely only on a few well-known benchmark three-dimensional (3D) exact solutions provided by pioneer works, namely, in the 1970s by Pagano as well as Srinivas for composite plates and later in the 1990s by Heyliger and Saravanos for piezoelectric composite plates. To overcome the limited number of test cases whose 3D exact solutions have been published, the method introduced by Heyliger to derive the 3D exact solutions has been successfully implemented using symbolic computing. New benchmark 3D exact free vibration solutions are provided for piezoelectric composite plates that complete a previous work with the static solutions. Two multilayered plates using PVDF piezoelectric material are chosen as test cases under three sets of electrical boundary conditions and considering three plate aspect ratios (from thick to thin plate), in a total of 18 test cases. For each case, the frequencies of the first six thickness modes are presented, along with some representative through-thickness mode shapes. [ABSTRACT FROM AUTHOR]

In this work, user-elements (UEL) in Abaqus are taken a step forward into the high-order layerwise modelling of variable stiffness composite laminates with curvilinear fibre paths, extending the limited number of available literature on refined multilayered UEL models. Two layerwise UEL models with three discrete layers are here proposed, assigning to each layer the displacements of the first- and third-order shear deformation theories, thus named UEL1 and UEL3, respectively. A complete assessment of the models predictive capabilities is carried out by a comparison with available static and free vibration solutions in the literature – either for constant or variable stiffness laminates – considering various boundary and loading conditions, as well as thin and moderately thick plates. Numerical results demonstrate that the developed models are capable to render fairly accurate and computationally efficient results, with particular emphasis on the higher-order model for predicting the global–local response behaviour of moderately thick plates. • Abaqus UEL models extended to high-order layerwise theories. • Assessment of UEL models for static and free vibration analysis. • Analysis of constant and variable stiffness composite laminates. • Comparison with 3D exact solutions for constant stiffness composites. • Comparison with available numerical solutions for curvilinear fibre laminates. [ABSTRACT FROM AUTHOR]

This work provides an assessment of layerwise mixed models using least-squares formulation for the coupled electromechanical static analysis of multilayered plates. In agreement with three-dimensional (3D) exact solutions, due to compatibility and equilibrium conditions at the layers interfaces, certain mechanical and electrical variables must fulfill interlaminar C 0 continuity, namely: displacements, in-plane strains, transverse stresses, electric potential, in-plane electric field components and transverse electric displacement (if no potential is imposed between layers). Hence, two layerwise mixed least-squares models are here investigated, with two different sets of chosen independent variables: Model A, developed earlier, fulfills a priori the interlaminar C 0 continuity of all those aforementioned variables, taken as independent variables; Model B, here newly developed, rather reduces the number of independent variables, but also fulfills a priori the interlaminar C 0 continuity of displacements, transverse stresses, electric potential and transverse electric displacement, taken as independent variables. The predictive capabilities of both models are assessed by comparison with 3D exact solutions, considering multilayered piezoelectric composite plates of different aspect ratios, under an applied transverse load or surface potential. It is shown that both models are able to predict an accurate quasi-3D description of the static electromechanical analysis of multilayered plates for all aspect ratios. [ABSTRACT FROM AUTHOR]

Abstract: The three-dimensional (3D) exact solutions developed in the early 1970s by Pagano for simply supported multilayered orthotropic composite plates and later in the 1990s extended to piezoelectric plates by Heyliger have been extremely useful in the assessment and development of advanced laminated plate theories and related finite element models. In fact, the well-known test cases provided by Pagano and by Heyliger in those earlier works are still used today as benchmark solutions. However, the limited number of test cases whose 3D exact solutions have been published has somewhat restricted the assessment of recent advanced models to the same few test cases. This work aims to provide additional test cases to serve as benchmark exact solutions for the static analysis of multilayered piezoelectric composite plates. The method introduced by Heyliger to derive the 3D exact solutions has been successfully implemented using symbolic computing and a number of new test cases are here presented thoroughly. Specifically, two multilayered plates using PVDF piezoelectric material are selected as test cases under two different loading conditions and considering three plate aspect ratios for thick, moderately thick and thin plate, in a total of 12 distinct test cases. [Copyright &y& Elsevier]

Abstract: A layerwise mixed finite element model is developed based on the least-squares formulation for the coupled electromechanical static analysis of multilayered plates with piezoelectric and composite layers. The model assumes a layerwise variable description for displacements, transverse stresses and in-plane strains, along with the electrostatic potential, transverse electric displacement and in-plane electric field components, taken as independent variables. This original choice for the layerwise mixed formulation is intended to ensure the a priori and complete fulfilment of the interlaminar C 0 continuity of both mechanical and electrical variables, which is due to compatibility and equilibrium conditions. Numerical applications are shown for assessment of the model predictive capabilities by comparison with available exact three-dimensional solutions, considering multilayered piezoelectric composite plates of various side-to-thickness ratios, under an applied load or surface potential. [Copyright &y& Elsevier]

Abstract: This paper presents a numerical assessment of different finite element models (FEM) for the static analysis of laminated composite beams of various cross-sections, considering equivalent single layer theories (Classical Lamination Theory – CLT, First-order Shear Deformation Theory – FSDT and Higher-order Shear Deformation Theories – HSDT). New mixed least-squares FEM are developed for all theories and confronted with displacement-based weak form, mixed weak form and mixed weighted residual form FEM, which are derived for comparison purposes. The governing equations consistent with the mixed formulations, derived from the Hellinger–Reissner variation principle, are also presented. A method of transforming the actual geometrical beam cross-section into an equivalent single layer, through transformation matrices and the parallel axis theorem, existing in the literature for the CLT is implemented and extended to the FSDT and HSDT. Validation and assessment of the different FEM involved the implementation of analytical solutions and comparison with numerical and analytical results available in the literature, from which conclusions in terms of accuracy and computational effort are drawn. [Copyright &y& Elsevier]

Abstract: A layerwise finite element model is developed in a mixed least-squares formulation for static analysis of multilayered composite plates. The model assumes a layerwise variable description of displacements, transverse stresses and in-plane strains, taken as independent variables. The mixed formulation allows to completely and a priori fulfil the known requirements, which refer to the zig-zag form of displacements in the thickness direction and the interlaminar continuity of transverse stresses, due to compatibility and equilibrium reasons, respectively. This contrasts with layerwise displacement-based models that usually cannot a priori account for the interlaminar continuity of transverse stresses. In addition, the benefit of mixed least-squares formulation, as opposed to mixed weak form models, is that it leads to a variational unconstrained minimization problem, where the finite element approximating spaces can be chosen independently. Numerical examples are shown to assess the layerwise mixed least-squares model predictive capabilities compared to three-dimensional elasticity solutions and also other finite element results available in literature. Most notably, the present model is able to achieve accurate results in very good agreement with three-dimensional solutions and is shown to be insensitive to shear-locking. [Copyright &y& Elsevier]

Abstract: Layerwise finite element models are developed based on a mixed least-squares formulation for both static and free vibration analysis of multilayered composite plates. The models assume a layerwise variable description of displacements, transverse stresses and in-plane strains, taken as independent variables. Altogether, the benefits of this finite element formulation are twofold. First, the layerwise mixed formulation enables the fulfilment of the so-called requirements, completely and a priori. Specifically, the interlaminar continuity of displacements and transverse stresses, due to compatibility and equilibrium conditions, are both in the form of C 0 continuous functions in the thickness z-direction. Second, the least-squares formulation leads to a variational unconstrained minimization problem, where the finite element approximating spaces can be chosen independently. Therefore, contrary to mixed weak form models, the mixed least-squares models are able to by-pass stability conditions, also known as inf-sup conditions. Ultimately, the model for static analysis yields a symmetric positive definite system of linear equations, whereas the model for free vibration analysis yields a symmetric quadratic eigenvalue problem. The numerical examples show that the models predictive capabilities are in excellent agreement with three-dimensional exact solutions, from very thick to very thin plates, and are shown to be insensitive to shear locking. [Copyright &y& Elsevier]

Abstract: This paper presents a mixed finite element model for the static analysis of laminated composite plates. The formulation is based on the least-squares variational principle, which is an alternative approach to the mixed weak form finite element models. The mixed least-squares finite element model considers the first-order shear deformation theory with generalized displacements and stress resultants as independent variables. Specifically, the mixed model is developed using equal-order C 0 Lagrange interpolation functions of high p-levels along with full integration. This mixed least-squares-based discrete model yields a symmetric and positive-definite system of algebraic equations. The predictive capability of the proposed model is demonstrated by numerical examples of the static analysis of four laminated composite plates, with different boundary conditions and various side-to-thickness ratios. Particularly, the mixed least-squares model with high-order interpolation functions is shown to be insensitive to shear-locking. [Copyright &y& Elsevier]

• Design optimization of FG sandwich plates under thermo-mechanical loadings. • Symmetric and non-symmetric sandwich plates with ceramic-metal-ceramic FG core. • Thermal and mechanical problems fully coupled using a layerwise mixed model. • FG core z-continuous effective properties described by high-order z-expansions. • Minimizing mass, deformation and stress, as measured by Tsai-Hill failure criteria. This work explores the multiobjective design optimization of symmetric and non-symmetric sandwich plates with ceramic-metal-ceramic functionally graded (FG) core, along with ceramic faces (if included), under thermo-mechanical loadings. The FG core is made of two functionally graded material (FGM) layers, each with the volume fractions of the constituent phases defined by a power-law function through-thickness, with the interface between them metal-rich and the core outer surfaces ceramic-rich. In line with symmetric or non-symmetric sandwich plates, the design variables involve the thickness of each FGM layer of the core and the index of its power-law function, along with the thickness of each ceramic face. The thermal and mechanical problems are fully coupled using a layerwise mixed least-squares model with multi-field independent variables, including, most importantly, displacements, temperature and transverse stresses. The FG core z -continuous effective properties are also fully described by high-order z -expansions, as demonstrated adopting the rule of mixtures. The multiobjective optimization problem is solved by Direct MultiSearch derivative-free method, minimizing mass, transverse displacement and the stress field, measured by Tsai-Hill failure criteria, all together. Numerical results provide optimal symmetric and non-symmetric sandwich plates with ceramic-metal-ceramic FG core, considering distinct constituent materials and including three-dimensional approximate solutions for validation. [ABSTRACT FROM AUTHOR]

This work addresses the multiobjective design optimization of metal-ceramic functionally graded (FG) plates, which are composed of a main functionally graded material (FGM) layer and may include metal and/or ceramic faces, under thermo-mechanical loadings. The design variables are the thickness of the FGM layer, the index of its power-law distribution of metal-ceramic volume fractions, and if included, the thickness of the metal and/or ceramic faces. The three objectives focus on mass, maximum transverse displacement and maximum value of the Tsai-Hill failure criteria to measure the stress field, aiming to minimize all together. Both thermal and mechanical problems are solved simultaneously using a layerwise mixed model based on least-squares formulation with multi-field independent variables, namely, displacements, temperature, transverse stresses, transverse heat flux, in-plane strains and in-plane components of the thermal gradient. The FGM layer z -continuous effective properties are fully described via high-order z -expansions, similarly to finite element approximations. The multiobjective optimization problem is solved by Direct MultiSearch (DMS) derivative-free method, which uses the notion of Pareto dominance to retain a list of feasible non-dominated solutions. Numerical results provide optimal designs of FG plates under thermo-mechanical loadings, exploring distinct metal-ceramic constituent materials and different side-to-thickness ratios, including three-dimensional approximate solutions for validation. [ABSTRACT FROM AUTHOR]

This work addresses the modelling and analysis of multilayered plates with embedded functionally graded material (FGM) layer(s) under hygro-thermo-mechanical loadings. The hygroscopic, thermal and mechanical problems are all solved simultaneously using a new layerwise mixed model based on least-squares formulation with multi-field independent variables, namely, displacements, temperature, moisture, transverse stresses, transverse heat flux, transverse moisture flux, in-plane strains and in-plane components of both thermal and moisture gradients. This mixed formulation ensures that interlaminar C 0 continuity requirements, where the material properties may actually change, are fully fulfilled a priori. An added feature is included to fully describe the FGM layer z -continuous effective properties through-thickness, using any homogenization method, by applying a high-order z -expansion to its effective properties, similarly to finite element approximations. The numerical results demonstrate the effects of hygrothermal environments in the analysis of distinct multilayered plates with embedded FGM layers, considering different side-to-thickness ratios, under a series of hygro-thermo-mechanical loadings. The rule of mixtures is used to estimate the FGM layer effective properties, including different material gradation profiles. Three-dimensional (3D) approximate solutions corroborate this model's capability to predict accurately a quasi-3D hygro-thermo-mechanical description of the through-thickness distributions of displacements and stresses, temperature and heat flux, moisture and moisture flux. [ABSTRACT FROM AUTHOR]

A new layerwise mixed model is developed for the coupled hygro-thermo-mechanical static analysis of multilayered plates, addressing hybrid composite laminates, fibre metal laminates and sandwich plates under hygro-thermo-mechanical loadings. This model is based on a mixed least-squares formulation, i.e. a strong form model, with a layerwise variable description for displacements, transverse stresses and in-plane strains, along with temperature, transverse heat flux and in-plane components of the thermal gradient, as well as moisture, transverse moisture flux and in-plane components of the moisture gradient, all taken as independent variables. This mixed formulation ensures that the interlaminar C 0 continuity requirements, where the material properties change, are fully fulfilled a priori by all independent variables. The effects of hygrothermal environments in the behaviour of multilayered plates are here demonstrated considering hybrid composite laminates, fibre metal laminates and sandwich plates with different side-to-thickness ratios under a series of hygro-thermo-mechanical loadings. Three-dimensional (3D) exact solutions are used to assess the results by the present model and some further by an alternative weak form model in the framework of Carrera Unified Formulation (CUF). The present model is shown to predict a highly accurate quasi-3D hygro-thermo-mechanical description of the through-thickness distributions of displacements and stresses, temperature and heat flux, moisture and moisture flux, all together. [ABSTRACT FROM AUTHOR]

The derivation of the piezoelectric equations requires only the Maxwell equations of electrostatics and the momentum equation with electric forces, together with the constitutive equations derived from the first principle of thermodynamics. In the non-isothermal case, the inclusion of thermal conduction requires also the second principle of thermodynamics and then the equation of energy becomes necessary. Furthermore, in the viscoelastic case, the viscous stresses modify the momentum and energy equations. The sequence outlined above provides the simplest derivation of the fundamental equation of anisothermal viscoelastic piezoelectricity including thermal and viscous dissipation. The equations of piezomagnetism are similar to those of piezoelectricity, replacing the electric by magnetic fields. The coupling of the unsteady electric and magnetic fields through electromagnetic waves interacts with both piezoelectricity and piezomagnetism leading to piezoelectromagnetism. In the general case of unsteady anisothermal piezoelectromagnetism, the energy, momentum and Maxwell equations specify the temperature, displacement vector, electric field and magnetic field. The coefficients involve constitutive and diffusion tensors specifying the properties of matter, generally anisotropic, such as crystals and orthotropic plates. They can also specify the properties of amorphous substances corresponding to the simplest isotropic case. • The equations of piezoelectricity are extended to include thermal stresses and conduction and viscoelastic effects. • The extension to piezoelectromagnetism combines unsteady piezoelectricity and piezomagnetism with electromagnetic waves. • Dissipative effects include thermal conduction and relaxation, Ohmic electrical conductivity and viscosity. • The equations are valid for general anisotropic materials as crystals or orthotropic plates, with isotropy a particular case. • The constitutive and diffusive tensors are defined from thermodynamic relations. [ABSTRACT FROM AUTHOR]

Abstract: Results of a comparative analysis between Heart Rate (HR) patterns occurring before the onset of Paroxysmal Ventricular Tachycardia (PVT) and from healthy subjects are shown. Two study groups were made after electrocardiographic dynamical monitoring (Holter) of volunteers. The first group includes 100h from 27 healthy control subjects, and the second group consists of 88h, ending with self-terminating episodes of PVT from 55 patients. Patterns are defined as sequences of consecutive RR intervals, while atypical patterns are defined as corresponding to unlikely behavior of Heart Rate in healthy subjects. We investigated spatial and temporal distributions of these patterns in order to find early signs of PVT. We found that they can be grouped on a reduced number of clusters, and the number of atypical patterns increases as we approach the onset of the episode. [ABSTRACT FROM AUTHOR]

Abstract In the competitive world of aircraft industry, the reduction of maintenance periods is a decisive factor when companies and arm forces are undergoing the procurement processes for the acquisition of their next fleets. Thus being, the investigation in the aeronautical sector today is focusing not only in the development of better and more reliable aircraft systems, but also in the development of techniques and tools that allow for the performance of the required maintenance tasks in faster and more optimized manners. This work arises within this field of investigation addressing the validation of innovative failure preventive equipment for the evaluation of the electromechanical impedance (EMI) response of aeronautical structures, and for the dynamic balancing of propellers of aircraft in the category of Normal, Utility, Aerobatic and Commuter. This work is divided into two parts, in which the first explores the accuracy and competitiveness of one alternative nondestructive test (NDT) equipment developed by Critical Materials S.A. in aeronautical applications, when compared to the classical NDT methods. This part ends with the assessment of the technique's capability to identify defects in one EPSILON TB-30 Nose Landing Gear of the Portuguese fleet which had been put out of service through a high-frequency eddy current inspection. The second part regards the development of a maintenance equipment for the dynamic balancing of propellers systems, specifically optimized for the dynamic balancing of the propeller of the Lycoming engine used in TB-30 aircraft of the Portuguese Air Force. This study ends by highlighting the gains achieved in the overall TB-30 maintenance costs with the use of the developed tool, by comparing the average time used for the process of balancing the Lycoming propeller, with and without the use of this tool. Highlights • The evaluation of the electromechanical impedance response of aeronautical structures was performed • The accuracy and competitiveness of one alternative nondestructive test equipment was explored • The validation of a failure preventive tool for aeronautical applications was carried out • The development and validation of an engine monitoring tool for the dynamic balancing of aircraft propellers was developed [ABSTRACT FROM AUTHOR]

Analysis of 21 episodes of vagal-induced atrioventricular block showed that the uncorrected QT intervals at the end of the corresponding RR pauses were not prolonged, in reference to the pre-block QT intervals, with pauses shorter than 1,280 ms. Subsequently, they gradually lengthened as the RR pauses progressively increased to 13,710 ms. This dynamic behavior of the QT interval in subjects without structural heart disease could have resulted from a complex interaction between the cumulative effects of previous cycle lengths (memory effect?) and the autonomic nervous system. [ABSTRACT FROM AUTHOR]

A subgroup of patients with neurocardiogenic syncope and negative electrophysiologic studies and adenosine tests (in 5 of 6 cases), who developed symptomatic paroxysmal atrioventricular block in the natural, ambulatory state, had positive tilt tests without advanced block. Lack of concordance between electrocardiographic changes may have reflected differential effects of the autonomic nervous system in the sinus and atrioventricular nodes, occurring in diverse circumstances and less likely because of the protocol used for tilt testing. [ABSTRACT FROM AUTHOR]

This study revealed that conventional temporal and spectral indexes of heart rate variability were reduced in patients with sinus tachycardia due to various, easily detectable, causes. These findings were attributed to the fast rates, per se, regardless of the cause, without reflecting a particular shift in the degree of autonomic activity and tone. [ABSTRACT FROM AUTHOR]

The modes of regression of very high degrees of atrioventricular nodal block (> or = 8:1) were studied in patients with atrial flutter and a specific variant of the tachycardia-bradycardia syndrome. The occurrence of reverse alternating Wenckebach periods, previously reported only in 2:1 atrioventricular block, emphasizes the complexities of multilevel block. [ABSTRACT FROM AUTHOR]

Analysis of heart rate variability in patients with inappropriate sinus tachycardia showed a 24-hour decrease in all temporal and spectral indexes, even after attempted correction to a rate of 75 beats/min. This may have resulted from a global decrease in parasympathetic activity or from a rapid sinus rate produced by other ill-defined mechanisms. [ABSTRACT FROM AUTHOR]