Honeycomb composites are common materials in applications where a high specific stiffness is required. Previous research has found that honeycombs with polymer infills in their cells exhibit effective stiffnesses greater than the honeycomb or polymer alone. Currently, the state of analytic models for predicting the effective properties of these honeycomb polymer composites is limited, thus further research is needed to better characterize the behavior of these materials. In this work, a nonlinear finite element analysis was employed to perform parametric studies of a filled honeycomb unit cell with isotropic wall and infill materials. A pinned rigid wall model was created as an upper bound on the deformable wall model’s performance, and an empty honeycomb model was employed to better understand the mechanisms of stiffness amplification. Mechanisms by which the stiffness amplification occurs is studied through parametric studies, and the results are compared to current analytic models. It has been observed that both the volume change within the honeycomb cell under deformation, and the mismatch in Poisson’s ratios between the honeycomb and infill influence the effective properties. Stiffness amplifications of over 4,000 have been observed, with auxetic behavior achieved by tailoring of the HPC geometry. This research provides an important step toward understanding the design space and benefits of honeycomb polymer composites, and demonstrates the possibilities for variable stiffness structures when considering smart material infill materials.

Composites can be tailored to specific applications by adjusting process variables. These variables include those related to composition, such as volume fraction of the constituents and those associated with processing methods, methods that can affect composite topology. In the case of particle matrix composites, orientation of the inclusions affects the resulting composite properties, particularly so in instances where the particles can be oriented and arranged into structures. In this work, we study the effects of coupled electric and magnetic field processing with externally applied fields on those structures, and consequently on the resulting material properties that arise. The ability to vary these processing conditions with the goal of generating microstructures that yield target material properties adds an additional level of control to the design of composite material properties. Moreover, while analytical models allow for the prediction of resulting composite properties from constituents and composite topology, these models do not build upward from process variables to make these predictions. This work couples simulation of the formation of microscale architectures, which result from coupled electric and magnetic field processing of particulate filled polymer matrix composites, with finite element analysis of those structures to provide a direct and explicit linkages between process, structure, and properties. This work demonstrates the utility of these method as a tool for determining composite properties from constituent and processing parameters. Initial particle dynamics simulation incorporating electromagnetic responses between particles and between the particles and the applied fields, including dielectrophoresis, are used to stochastically generate representative volume elements for a given set of process variables. Next, these RVEs are analyzed as periodic structures using FEA yielding bulk material properties. The results are shown to converge for simulation size and discretization, validating the RVE as an appropriate representation of the composite volume. Calculated material properties are compared to traditional effective medium theory models. Simulations allow for mapping of composite properties with respect to not only composition, but also fundamentally from processing simulations that yield varying particle configurations, a step not present in traditional or more modern effective medium theories such as the Halpin Tsai or double-inclusion theories.

As materials and engineering design tools become more complex, engineers are looking to mimic structures and systems, occurring in nature, to design more efficient mechanical structures. One such structure is a morphing composite lattice structure, whose design was inspired by the tail of the bacteriophage T4 virus [1]. To date the morphing behavior of the tail structure of the virus has been simplified by neglecting the intermolecular mechanisms that actuate the bistable behavior of the tail. This behavior has been achieved using prestressed composite flanges that are mechanically joined in alternating clockwise and anti-clockwise chiralities. The composite lattice structure has previously been proposed as an actuator for aerospace structures, replacing more complex and heavier traditional actuator structures. McHale et al. [2] have shown that the composite lattice is capable of greatly improving upon the state-of-the-art in the form of a telescopic boom for CubeSat systems. This utility provides validity in studying further enhancements on the capabilities of the structure to enhance its potential applications in the aerospace industry. This work proposes a mechanism for replicating the inter-molecular behavior that occurs in the bacteriophage T4 tail. The bonds between the inner and outer tail structures are broken and reformed, thus, driving the actuation process. This method will form a variable topology morphing system. As such, a novel category of morphing structure is presented here for the first time. The morphing topology behavior is proposed by replacing mechanical fasteners in the traditional lattice structure in select locations with a series of permanent magnets. Finite element analysis is used to calculate the difference in energies between the states before and after discrete topology changes occur, allowing the associated change in energy to be converted to a required actuation force. Varying the topology of the lattice structure allows the lattice to transition from a linear morphing actuator system to a bespoke and tunable curved actuator with potential applications in satellite dish actuation, for example.

Multifunctional Structures for Attitude Control (MSAC) is a new spacecraft attitude control system that utilizes deployable panels as multifunctional intelligent structures to provide both fine pointing and large slew attitude control. Previous studies introduced MSAC design and operation concepts, simulation-based design studies, and Hardware-in-the-Loop (HIL) validation of a simplified prototype. In this article, we expand the scope of design studies to include individual compliant piezo-electric actuators and associated power electronics. This advance is a step toward high-fidelity MSAC system operation, and reveals new design insights for further performance enhancement. Actuators are designed using pseudo rigid body dynamic models (PRBDMs), and are validated for steady-state and step responses against Finite Element Analysis. The drive electronics model consists of a few distinct topologies that will be used to evaluate system performance for given mechanical and control system designs. Subsequently, a high-fidelity multiphysics multibody MSAC system model, based on the validated compliant actuators and drive electronics, is developed to support implementation of MSAC Control Co-design optimization studies. This model will be used to demonstrate the impact of including the power electronics design in the Optimal Control Co-Design domain. The different control trajectories are compared for slew rates and the vibrational jitter introduced to the satellite. The results from this work will be used to realize closed-loop control trajectories that have minimal jitter introduction while providing high slew rates.

Magnetoelectric (ME) composites are viable candidates for use in numerous applications owing to their multifunctional capabilities. These composites develop voltages across the piezo-electric phase under external magnetic fields. Numerous models available in literature consider the magnetostriction under pure magnetic loading. However, fabrication of ME composites results in development of compressive stresses on the magnetostrictive layer, which leads to a poor ME response and hence an initial effective tensile prestress to the magnetostrictive phase is required to either compensate or enhance the ME coupling. In this work, the ME response of an unsymmetric laminate is predicted using a finite element procedure based on Mindlin plate theory, giving due consideration the magnetostrictive nonlinearity, the direction of the applied field and the effect of the stress state on the magnetostrictive response. The model predicts that initial shear stresses, positive or negative, provide the best enhancement to the ME coupling.

Combined finite element and network modeling methods provide a time efficient instrument to simulate multi-physics systems. In this work, the Combined Simulation is applied to a nonlinear electromagnetic energy harvester with electrical interface circuit and capacitive energy storage. The energy harvester consists of two cylindrical permanent magnets placed in a cylinder with opposite directions to each other, whereas one magnet is fixed and the other magnet is freely movable in the vertical direction within the cylinder. A coil surrounds the cylinder and transforms the magneto-mechanical energy into electrical energy by means of electromagnetic induction. An external force with a certain wave-form excites the system. Finite element and network modeling methods are combined to determine concentrated and distributed network parameters and to describe the nonlinear system as an equivalent circuit, whereas Finite element modeling of the two permanent magnets reveals the repulsive force at different distances. The position-dependent electromagnetic coupling coefficient is employed by calculating the linked magnetic flux gradient. The system performance, including the interface circuit and an energy storage component, is then predicted using the numerical network simulator LTspice. A voltage doubler is used to charge a capacitor and compared with a one-way and two-way rectifier. The voltage doubler shows the best results and charges the capacitor to the highest voltage. The presented method helped to understand the overall system behavior. Physical quantities can be quickly determined in the network. The method can be applied to other multi-physics systems and to more complex interface circuits, easily.

Flexible actuators are a growing class of devices implemented in soft robotic applications, medical devices and processes involving food and pharmaceutical products. Such actuators have traditionally been manufactured using casting processes or other conventional methods requiring more than one fabrication step. The arrival of flexible 3D printing materials and 3D printing techniques has facilitated the creation of these flexible actuators via additive manufacturing. The work presented in this article displays the analytical characterization and experimental validation of two materials and two actuator designs. The first case presents a finite element analysis (FEA) simulated model of a bellows actuator using a photocurable flexible resin (TangoPlus FLX930) and studies the effect of printing orientation on the simulation. The simulation used a 5 parameter Mooney-Rivlin model to predict the strain behavior of the actuator under hydrostatic pressure. A second case is presented where a Thermoplastic Polyurethane actuator was 3D printed and simulated using the same FEA model and a second calibration of the Mooney-Rivlin 5 parameter model. In both cases experimental data was used to calibrate and validate the simulation. The resulting simulated strain was consistent when the printing orientation of actuators was parallel (0 degrees) to the strain direction of the actuators. Results were less consistent when a print orientation of 45 degrees was applied.

The ability of a material to display two equilibrium states, called bistability, has been previously observed in carbon fiber reinforced polymers (CFRPs). For bistability to occur, the laminate must consist of an unsymmetric layup about its midplane which generates internal residual stress from thermal contraction. Prior studies have observed bistability in CFRPs with small-scale rectangular geometries where all sides were less than 250 mm. The aim of this paper is to demonstrate the existence of bistability in large-scale CFRPs with rectangular and non-rectangular geometries. Experiments and finite element analyses were conducted to determine the viability of bistability in large-scale CFRPs where at least one length aspect of the specimen was greater than or equal to 304.8 mm. Specimens whose shapes included rectangles, deltoids, triangles, and circles, were fabricated and tested to determine the presence of bistability and the associated curvature for each cured equilibrium state. Rectangular specimens had a side length of 914.4 mm and widths that varied from 177.8 to 457.2 mm. For the deltoids, triangles, and circles, one length aspect (i.e. the height, hypotenuse, and diameter, respectively) equaled 304.8 mm. Finite element models were created to compare the equilibrium shapes’ curvatures and displacements with the experimental laminates; the existence of bistability was also examined using a nondimensionalized bifurcation plot. Experimentally, bistability was found to occur for the fabricated laminates up to six plies. As the studied laminates could be considered thin, they displayed cylindrical cured shapes. The non-traditional shaped CFRPs followed bistability trends found for traditional, small-scale, rectangular laminates. An inverse relationship between the ply count and curvature was exhibited for the large-scale, rectangular laminates; curvature decreased as the number of plies in the laminate increased.

Composite laminates constructed in an asymmetric layup orientation of [0 i , 90 i ], i > 0, exhibit two stable equilibrium positions and may be actuated to snap from a primary cure shape to an inversely related secondary stable shape. This study aims to aid in developing a comprehensive description of thick bistable laminates, whose increased thickness risks the loss of bistability, through previously established analytical approaches and verification via experimentation. The principle of minimum potential energy is applied to two materials and analyzed using the Rayleigh-Ritz minimization technique to determine the cure shapes of carbon fiber reinforced polymer laminates composed of AS4/8552 and TR50S-12k carbon fibers. These materials were modeled to act as square thick bistable laminated composites with sidelengths up to 0.914m. Visualizations of the out-of-plane displacements are shown with a description of the Rayleigh-Ritz analysis. Additionally, a finite element model (FEM) created in Abaqus CAE 6.14 and experiments using DA409/G35 and TR50S-12K/NP301 prepreg were used to further describe and develop the fundamental description for thick bistable laminates in terms of loss of bistability, actuation load, and principle shape. The analytical model is an extension of Hyer’s (2002) and Mattioni’s (2009) work applied to thick bistable laminates where the primary assumption was the x-axis curvature equaled the negative y-axis curvature for the primary and secondary stable positions, respectively. This assumption leads to the already cemented conclusion that bistable laminates, once cured, take on one of two inversely related paraboloid shapes. FEA simulations contradicted this by showing an average 11% difference in curvature magnitude for the aforementioned shapes. Furthermore, fourth order polynomials were used to describe the curvature along the axes, differing from the previously used Menger curvatures, (three-point approximation). Bifurcation plots using peak deflections and average curvature generated from FEA simulations clearly showed bistability existed to approximately 50 plies; however, the energy landscape plots indicated a significant degradation of bistability starting at 36 plies. Experimentation was performed on a test stand mimicking the same boundary conditions used in FEA while applying a central out-of-plane load. Experimental observations showed decreased peak displacements of stable cure shapes. Observations also indicated that the x-axis curvature had a significant difference in magnitude compared to the negative y-axis curvature. However, the existence of bistability agreed with FEA energy landscape plots, with clear “snaps” ending at thicknesses of 28–36 plies. Moreover, actuation force was found to correlate well with FEA simulations. Differences in the critical point can be attributed to the combination of material property differences for DA409 and TR50S-12K, failure to capture polymer relaxation, limitations of the experimental setup, and hand layup fabrication errors. Lastly, this paper adds viability of thicker laminates for use in macroscale applications where shape morphing or shape-retention attributes are a necessary constraint, although only where low loads are expected.

Real-time model updating of active structures subject to unmodeled high-rate dynamic events require structural model updates on the timescale of 2 ms or less. Examples of active structures subjected to unmodeled high-rate dynamic events include hypersonic vehicles, active blast mitigation, and orbital infrastructure. Due to the unmodeled nature of the events of interest, the real-time model updating algorithm should circumvent any model pre-calculations. In this work, we present a methodology that updates the finite element analysis (FEA) model of a structure experiencing varying dynamics through online measurements. The algorithm is demonstrated for a testbed, comprised of a cantilever beam and a roller that serves as movable support. The structure’s state is updated (i.e. the position of the moving roller) by continuously updating the associated FEA model through an online adaptive meshing and search algorithm. The structure’s state is continuously estimated by comparing the measured signals with FEA models. New FEA models are built based on the enhanced estimate of the structure’s state through adaptive meshing for modal analysis and adaptive search space for the FEA model selection. The proposed methodology is verified experimentally in real-time using the testbed. It is demonstrated that the adaptive features can achieve accurate state estimations within the required 2 ms timescale.

The so-called solid-state ornithopter concept seeks to employ piezoelectric materials to generate flapping motion instead of relying on conventional mechanisms and multi-component actuation systems. The motion can be induced on a wing-like partially-clamped composite substrate with a piezocomposite device (i.e. the Macro-Fiber Composite actuator.) In this research, a design for a flapping wing is proposed based on the analysis of critical system parameters such as geometric properties and boundary conditions. A series of finite element simulations are conducted based on the variation of those parameters. Consequently, the effects of parameters on the structural response is studied. Also, modal analysis is done to examine the effects of geometric parameters on the resonant frequencies of the system. Heaving and pitching responses are examined.

The steam sterilization of reusable medical instruments is a critical process. Standardized treatments with hot, saturated steam at maximum temperatures of up to 138 °C often represent a significant thermal load, which is repeated with varying number of cycles depending on the medical device. Until now, there is no possibility for medical device manufacturers to monitor how often a product has been sterilized. However, this is necessary for both safety and warranty issues, since according to the European Medical Device Regulation (EU-MDR), the manufacturer must specify how often a product can be sterilized. In this paper the actuator approach for a micromechanical “sterilization cycle counter” is presented. It is designed to autonomously record, count and store steam sterilizations directly on the instrument by combining silicon micromechanics with shape memory alloy (SMA) actuators. This enables an autonomous operation without additional energy sources such as batteries. During the steam sterilization cycle, a certain temperature limit is exceeded once and detected by the SMA. The system development aims at the heterogeneous integration of standard SMA wires into a silicon microstructure. The transformation temperatures of the SMA is thereby increased to the relevant range by prestressing. In detail, the paper first describes the approach of the counting mechanism and the possibilities and limitations of implementing and pretensioning of SMA wires in silicon microstructures. Based on that, the development of the SMA actuator geometry using an SMA Finite Element Analysis (FEA) model according to the approach of Aurichio is described. The model is validated using an up-scaled test bench of the system, in which various geometric parameters can be varied. Finally, the results will be discussed in particular regarding the MEMS process chain to be carried out in the next step.

This paper presents a design study of adaptive skins that enable thermal regulation for buildings. The skins consist of rectangular panels that adaptively open and close driven by shape memory alloy (SMA) wires in response to the variation of the environment temperature. The SMA wires are used as both thermal sensors and actuators that inspect the environmental temperature and provide a corresponding actuation response. When temperature is low, the SMA wires are stable in their elongated martensitic configuration, keeping the panels closed to maintain the building interior warm by reducing incoming airflow from the exterior. When temperature reaches the SMA austenite transformation values, the SMA wires transform into their contracted austenitic configuration and open the panels. This permits cooling of the building interior by allowing circulation of incoming airflow from the exterior. This repeatable response allows the skins to adaptively regulate the indoor temperature. The performance of the adaptive skins is evaluated using finite element analysis. Metallic and laminated fiber-reinforced composite plates are explored as material options for the panels. The adaptive skins are parameterized using design variables including the dimensions of the panels, the ply thickness and orientation angles in the case of fiber-reinforced panels, and the radii of the SMA wires. By employing genetic algorithms, these design variables are optimized to maximize the achievable opening area of the panels while satisfying material failure constraints.

Origami-inspired structures and material systems have been used in many engineering applications because of their unique kinematic and mechanical properties induced by folding. However, accurately modeling and analyzing origami folding and the associated mechanical properties are challenging, especially when large deformation and dynamic responses need to be considered. In this paper, we formulate a high-fidelity model — based on the iso-parametric Absolute Nodal Coordinate Formulation (ANCF) — for simulating the dynamic folding behaviors of origami involving large deformation. The center piece of this new model is the characterization of crease deformation. To this end, we model the crease using rotational spring at the nodes. The corresponding folding angle is calculated based on the local surface normal vectors. Compared to the currently popular analytical methods for analyzing origami, such as the rigid-facet and equivalent bar-hinge approach, this new model is more accurate in that it can describe the large crease and facet deformation without imposing many assumptions. Meanwhile, the ANCF based origami model can be more efficient computationally compared to the traditional finite element simulations. Therefore, this new model can lay down the foundation for high-fidelity origami analysis and design that involve mechanics and dynamics.

Nitinol in the form of wires, tubes, and plates have been explored extensively; however, the characteristics of Nitinol as a woven fabric have so far been little-studied analytically. It would be easier to design such a fabric if conventional fabric models were known to apply to Nitinol fabrics, potentially with modifications required by Nitinol’s unique properties. A 25 mm wide Nitinol narrow fabric has been manufactured using traditional weaving equipment using a proprietary process that achieves a uniform and tight weave. Heat-treatment and straight shape-set is applied to a single Nitinol wire and the woven Nitinol fabric at 600°C for 30 minutes. The 0.25 mm Nitinol wire constituent was tested using differential scanning calorimetry (DSC) to determine the transition temperatures ( M f , M s , A s , and A f ), which were found on average to be 54.5°C, 66.9°C, 88.7°C, and 103.5°C respectively. Both the Nitinol wire and fabric were tested in a temperature-controlled chamber (testing temperatures ranged from room temperature to 200°C) in which the tensile stress-strain characteristics were observed. It was determined that existing analytical models can be employed to accurately estimate the overall tensile stiffness of woven Nitinol fabrics in a small-strain regime. Additionally, it was confirmed that the tensile loading of woven Nitinol fabric can be modeled in MSC.Adams with beam elements. In combination with the geometric model presented, woven Nitinol fabric behavior can be predicted from the experimental behavior of the constituent Nitinol wire.

Shape memory polymers (SMPs) are extensively studied for self-folding origami due to their large strain recovery, low cost, and low activation energy. SMPs utilize viscoelastic material behavior to change shape in response to an applied stimulus, for instance light or electricity. Electrical actuation is desirable due to its higher energy density and shorter response time. Previous studies reported empirical results on shape recovery of conductive polymer composites actuated by specific applied voltage or current conditions, which required rigorous experimentation. Here, we introduce a finite element framework capable of predicting the coupled electro-thermo-mechanical response of electrically actuated SMPs. As inputs, this framework requires material properties, such as electrical conductivity and viscoelastic parameters. The viscoelastic response is implemented using a Prony series model that is fit to experimental dynamic mechanical analysis (DMA) data. Using this framework, we predict the shape recovery behavior of electrically actuated SMPs subject to various thermal, electrical, and mechanical loads and evaluate the sensitivity of the response to the material properties. Additionally, we show the effects of material pre-straining conditions and localized conductive pathways on shape recovery and self-folding. This computational framework provides a fundamental understanding of the electro-thermo-mechanical response of electrically actuated SMPs and can be used to design electrically actuated self-folding origami for aerospace applications.

A self-powered, and self-actuating lithium ion battery (LIB) has the potential to achieve large deformation while still maintaining actuation force. The energy storage capability allows for continual actuation without an external power source once charged. Reshaping the actuator requires a nonuniform distribution of charge and/or bending stiffness. Spatially varying the state of charge and bending stiffness along the length of a segmented unimorph configuration have the effect of improving the tailorability of the deformed actuator. In this paper, an analytical model is developed to predict the actuation properties of the segmented unimorph beam to determine its usefulness as an actuator. The model predicts the free deflection, blocked deflection, and blocked force at the tip as a function of spatially varying state of charge and bending stiffness. The main contribution of the paper is the development of blocked deflection over the length of the segmented unimorph, which has not yet been considered in the literature. The model is verified using experimental data and commercial finite element analysis.

We propose a planar hydrogel-based micro-valve design which is modeled as a library element for Matlab Simulink. For this test case, a pressure pump (voltage source) in series with a micro-valve model (variable fluidic resistance) is built up. The micro-valve subsystem is separated in four main parts. Based on the applied temperature stimulus, the equilibrium length is determined according to an experimentally verified fit function. Furthermore, the equilibrium length considers a static hysteresis effect which is modeled in analogy to the saturation of magnetization in electric transformers. In a second step, the transient behavior follows a first order differential equation, but the cooperate diffusion coefficient is size dependent affecting the rise time of the system. This causes a faster swelling than deswelling of the hydrogel. In the third section, the stiffness property is implemented to calculate the maximum sealing pressure and the resulting gap between the hydrogel and the wall. The fluidic resistance of the micro-valve considers a three-dimensional geometry and is calculated based on a look-up table, extracted from a fluid-structure-interaction (FSI) model generated from a finite element structure. The proposed model allows a full description of the fluidic hydrogel-based micro-valve and is part of an upcoming microfluidic toolbox for Matlab Simulink containing passive elements and optional chemical reactions like mixing fluids and enzyme reactions for future applications.

It has been amply demonstrated that the development of SMA actuators has a great potential of application in several branches of industry. Obviously, the efficiency of the actuators depends both on the inherent features of the materials they are made of and the geometric characteristics of the devices. This work considers a particular type of actuator first conceived by [1], consisting in the association of two cantilever beams, the first presenting the shape memory effect and the second presenting the superelastic effect, coupled mechanically so as to guarantee two equilibrium positions and thus a stand-alone cyclic actuator, in which the superelastic beam provides the bias action. Numerical simulations of the behavior of the actuator are performed using the commercial finite element software COMSOL, which implements the Boyd-Lagoudas thermomechanical model. The goal of the simulations is to characterize the actuation range of the actuator, in terms of maximum displacement obtained at the tip. The effect of the dimensions of the beams on the tip displacement under some load scenarios is investigated. The results provide guidelines for the design of the actuator to fulfill specific requirements, also suggesting the use of numerical optimization for the optimal design of the actuator accounting for constraints.

This paper proposes a probabilistic model for the placement of sensors that considers uncertain factors in the sensing system to find the best arrangement of sensor locations. Traditional procedures for structural health monitoring (SHM) usually rely on simplified behavior and deterministic factors from structure’s response. Incorporating the sources of uncertainty (e.g., loading condition, material properties, and geometrical parameters) in the design of sensor network will enhance the safety and extend the useful life of the complex mechanical systems. The proposed method is defined in a reliability-based design optimization framework to search for the sufficient number of sensors for failure detection using Genetic Algorithm. The optimal arrangement is found as the one that minimizes the number and size of sensor patches and maximizes the expected probability for failure detection. This design concept involves a new failure diagnosis indicator, named detectability, formulated based on the Mahalanobis Distance (MD). MD distribution is used as a measure of the quality of the obtained sensor configuration suitable for many sensing/actuation SHM processes, while considering the uncertainties such as those from structure properties and operation condition. The MD classifier categorizes large sets of testing data by comparing the distances of the mean with the distribution of available training data sets. Statistical evaluation of failure detectability can be obtained by comparing the distribution of MD for different failure modes. Kriging modeling, used for metamodel-based design optimization, is applied for surrogate modeling of the stochastic performance of system to reduce computational cost. The surrogate model is constructed by correlating the sensor output to the vibration pattern of the structure and sensor variable inputs (e.g., size and location). Direct finite element analysis (FEA) evaluates the sensor output with respect to the input variables. Consequently, the constructed kriging model enables the estimation of sensor output for any arbitrary sensor arrays. As a case study, a rectangular panel with a size of 40 cm × 30 cm is considered that is fastened using eight screw joints. The harmonic vibration force is applied to the center of the plate and its varied vibration pattern is used to detect the joint failure. Eight different combinations of join failure are defined as health statuses (failure modes), and different size and layouts of the piezoelectric sensors are considered to detect the health status. The results verify the capabilities of the new method for failure diagnosis of screw joints in a panel with high sensitivity of fault detection.