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Abstract: Mechanical joints in assembled structures cause energy dissipation due to micro-slip in contact and softening effects that play an important role in the dynamic behavior of such structures. The contact non-linearity is governed by micro and meso-scale parameters (geometry, roughness, local pressure, etc.) and as a result cannot be included in a macro-size model of a whole structure because of the computational cost. The present paper investigates the idea of using the normal modes of the linearized structure as boundary conditions on a detailed model reduced to the joints only. Since contact non-linearities alter mode shapes, they are corrected as vibrational energy increases. The method relies on a corrected quasi-static formulation associated with the Masing hypothesis. These assumptions circumvent considerable numerical expense due to the non-linear dynamics. The formulation of the method is detailed and investigated on a lap-joint benchmark. [Copyright &y& Elsevier]

Abstract: This paper deals with the damping caused by friction in joints. A new test bench is presented and justified by comparisons made with devices described in the literature. The purpose of this academic bench is to measure the damping induced by partial slip and friction in a planar joint. Moreover, allows uncoupling normal static and dynamic tangential forces. A new method for so-called stopped-sine excitation was developed. It allows more precise monitoring of the evolution of the vibration frequency and damping of non-linear modes. This method is associated with piezoelectric exciters for greater efficiency when stopping excitation. A large number of experimental results are presented and discussed. They are used to characterize the damping induced by micro-sliding in the bonds. [Copyright &y& Elsevier]

Abstract: The operating deflection shape of a pad during squeal noise is measured on a real brake system with three-axis accelerometers. A time-frequency analysis is performed that highlights the dependency of squeal on the hydraulic pressure of the system and shows that squeal occurs simultaneously with harmonic components. The operating deflection shape of this pad before and during squeal is then visualized using interpolation, showing the predominance of bending motion. Finally, the pad motions observed are compared to the real modal basis of a detailed Finite Element model. [Copyright &y& Elsevier]

In the context of brake system simulation, the highlight of phenomenon like squeal needs specific methods. We will focus on stability analysis by complex modal analysis. The use of damping system called shims for squeal noise reduction implies that simulations take into account the damping of materials. To do this, we use parametric viscoelastic models and particularly the generalised Maxwell model. Work consisted in tools choice and validation (viscoelastic models, finite elements formulations, ...) and in simulation method implementation. It was divided in several steps. In a first step, we have selected, among several mathematical models able to describe viscoelasticity, the best for damping modelisation in brake systems. We studied the complex modulus model, the Kelvin-Voigt model and the generalised Maxwell model. In a second step, we sought a formulation of the finite element problem adapted to the modal analysis. We then used a state space model formulation. A capital hypothesis on the equality of the pole of the generalised Maxwell model permits to reduce the size of the model and in the same time to simplify its formulation. Finally, the developed methods have been applied to simulate a pad and a full brake system. The influence of the number of modes used in model reduction and the order of the Maxwell model has been quantified in parametric studies. In the pad case, we performed a complex modal analysis with friction material considered as viscoelastic. The objective was to update the pad frequencies and damping according to FRF measures. In the brake case, we performed a complex modal analysis with the two friction materials and one shim considered as viscoelastic. This model has also been used to exhibit the link between the strain energy distribution in the brake and the damping level obtained by complex modal analysis. To conclude, we developed a simulation method using Abaqus® and Matlab® for the complex modal analysis with viscoelasticity effects and Python to make data exchange between Abaqus® and Matlab® possible. This method permits to perform stability analysis with several viscoelastic materials, on large models, without degradation of computation time. [ABSTRACT FROM AUTHOR]

New laboratory tests are presented for the experimental evaluation and assessment of the piezoceramic shunted damping (PSD) concept for cantilever Aluminium thin (long) beams bonded symmetrically on their upper/lower surfaces with single pairs of small piezoceramic patches. Following these tests out- come, the PSD efficiency measure is proposed to be the so-called modal effective electromechanical coupling coefficient, which is post-processed from free-vibrations analyses under short-circuit and open-circuit electrodes of the patches. For this purpose, the tests are numerically modelled, analysed, and correlated using ABAQUS® commercial finite element (FE) code. Good tests/models correlations were reached after FE models electromechanical updating. This is attributed to the refined FE models in the sense that they have considered realistic and desirable features such as, electrodes equipotentiality, piezoceramic patches poling orientations (same/opposite), and the corresponding (parallel/series) electric wiring (connections). [ABSTRACT FROM AUTHOR]

This study presents a concept for a straightforward method to enhance the actuation performances of magneto‐active elastomer membranes. The concept is based on a characteristic magnetization pattern and offers a solution to two major difficulties in the actuation of thin and mechanically soft magnetic actuators: the localization of actuation forces and the self‐demagnetization. After the magnetization process, the membrane presents two regions with an oppositely oriented out‐of‐plane magnetization. The magnetized regions are separated by a transition zone which is called magnetic pole transition. Experimental investigations reveal a high magnetic flux density near the pole transition—even in the center of bidirectionally magnetized membranes—whereas the magnetic flux density of a uniformly magnetized membrane decreases toward the center. In additional experiments, membranes with both magnetization patterns are actuated by stiff permanent magnets. The resulting out‐of‐plane displacement of the bidirectionally magnetized membrane exceeds the displacement of the unidirectionally magnetized membrane by far. The investigations demonstrate that this enhancement stems from the presence of the magnetic pole transition. All experiments are reproduced using magnetic and magneto‐mechanical numerical models; a good accordance between the results is achieved. [ABSTRACT FROM AUTHOR]

Friction modeling is essential in a vast amount of engineering applications. In this paper Mindlin contact friction model, a Masing rule compliant model, is manipulated in order to find a correlation with Dahl dynamic friction model, a Masing rule not compliant model. The resulting equations are then numerically compared and the correlation demonstrated with several loading functions. The result is a modified Dahl model that captures the partial slip behavior following the contact theory. The Dahl model, classically used in control engineering as an empirical model due to its implementation facility, finds in this new formulation a physical meaning to its parameters and finally identified physical parameters (according from Mindlin model) for the Dahl model. [ABSTRACT FROM AUTHOR]

The interpretation of unlabeled acoustic emission (AE) data classically relies on general-purpose clustering methods. While several criteria have been used in the past to select the hyperparameters of those algorithms, few studies have paid attention to the development of dedicated objective functions in clustering methods able to cope with the specificities of AE data. We investigate how to explicitly represent clusters onsets in mixture models in general, and in Gaussian Mixture Models (GMM) in particular. We propose the first clustering method able to provide, through parameters estimated by an expectation–maximization procedure, information about when clusters occur (onsets), how they grow (kinetics) and their level of activation through time. This new objective function accommodates continuous timestamps of AE signals and, thus, their order of occurrence. The method, called GMMSEQ , is experimentally validated to characterize the loosening phenomenon in bolted structure under vibrations. A comparison with four standard clustering methods on raw streaming data from five experimental campaigns shows that GMMSEQ not only provides useful qualitative information about the timeline of clusters, but also shows better performance in terms of cluster characterization. [Display omitted] • First AE clustering objective function with clusters onsets, kinetics and activation. • Clusters onsets provide useful insights on AE data streams for monitoring purposes. • Possibility to make the method physics-informed by including prior on onsets. • Shared codes and benchmark datasets with seven classes related to bolts loosening. [ABSTRACT FROM AUTHOR]

The design of complex engineering structures largely relies on computational intelligence in the form of science-based predictive models to support design decisions. This approach requires modeling and manufacturing uncertainties to be accounted for explicitly and leads to an inescapable trade-off of performance for robustness. To remedy this situation, a novel self-design paradigm is proposed that closes the loop between the design and manufacturing processes by leveraging physical intelligence in the form of real-time experimental observations. This allows the real-time product behavior to participate in its own design. The main benefit of the proposed paradigm is that both manufacturing variability and difficult-to-model physics are accounted for implicitly via in situ measurements thus circumventing the performance-robustness trade-off and guaranteeing enhanced performance with respect to standardized designs. This paradigm shift leads to tailored design realizations which could benefit a wide range of high performance engineering applications. The proposed paradigm is applied to the design of a simply-supported plate with a beam-like absorber introduced to reduce vibrations based on an equal peaks performance criteria. The experimental setup includes a low-cost 3D printer driven by a simple decision algorithm and equipped with an online vibration testing system. The performances of a small population of self-designed plates are compared to their standardized counterparts in order to highlight the advantages and limitations of the new self-design manufacturing paradigm. [ABSTRACT FROM AUTHOR]

This paper proposes a new lap-joint configuration, the so-called Orion beam. The new setup is composed of two thin beams connected by three bolted joints with contact patches on each connecting bolt. The Orion beam suggests an assembly configuration, in which there are bolts dedicated to "static" functions to guarantee structural integrity and those that perform "damping" functions to increase energy dissipation due to frictional contact. In particular, this paper analyzes the influence of the Orion beam's design in the repeatability of experimental measurements and the impact of the tightening torque and excitation amplitudes on the system's response. A feedback controller is proposed to control the excitation amplitudes during step-sine tests in the vicinity of resonance frequencies to measure the frequency response curves used to perform such analysis. Additionally, a single-degree-of-freedom Duffing–Van der Pol oscillator is proposed to evaluate, through its calibrated parameters, the impact of several tightening torque conditions and multiple excitation amplitudes on the structural stiffness and damping considering the vibration mode that promotes pronounced deformation around the lap-joint. Due to the presence of contact patches, the results show that the structure maintained impressive repeatability after several experimental measurements. Besides, it is possible to increase the damping for amplitude attenuation without significant losses in the contact stiffness. • The Orion beam is presented. The new lap-joint has contact patches performing "static" and "damping" functions. • A step-sine excitation strategy is developed to control excitation amplitudes. • Studies dedicated to the measurement repeatability, influence of the tightening torque and excitation amplitudes are presented. • A Duffing–Van der Pol oscillator is proposed to approximate the Orion beam's response. • The Orion beam's design enhances the vibration attenuation through the damping patches without compromising the structural integrity. [ABSTRACT FROM AUTHOR]

This paper proposes a novel self-adaptive strategy to control piezoelectric vibration absorbers (PVA) using a semi-passive resonant shunt with tunable inductance for vibration attenuation of harmonically excited structures. The tunable inductor is realized using ferrite cores and its inductance is controlled by means of the air gap effect between the cores using piezoelectric stack actuators. This device allows the control of the resonance frequency of the shunt circuit. The adaptive resonant shunt leverages the effect of antiresonance resulting from the electromechanical coupling of the structure with a resonant shunt with low electrical damping to attenuate the vibration of the harmonically excited structure. A machine learning control method based on a Gaussian process regression model is used to drive the tunable inductance based on minimizing the time-averaged RMS response of the structure. The experimental application of the proposed strategy is illustrated in an application to attenuate a single-mode of a simplified aircraft fuselage structure. A reduction of about 30% in the maximum vibration amplitude is observed by comparing the self-adaptive resonant circuit and a traditional resonant circuit designed based on the equal-peaks method. • Self-adaptive piezoelectric vibration absorber for vibration attenuation in harmonically excited structures. • A novel semi-passive tunable resonant shunt based on airgap control between ferrite cores. • Supervised machine learning control algorithm using the Gaussian Process regression model. [ABSTRACT FROM AUTHOR]

Abstract: This work describes an automatic method for removing modulated sinusoidal components in signals. The method consists in using the Optimized Spectral Kurtosis for initializing Series of Extended Kalman Filters. The first section is an introduction to vibration applications with Kalman Filters and modulated sinusoids. The detection process with OSK is described in the second section. The third section concerns the tracking algorithm with SEKF for amplitude and frequency modulated sinusoidal components. The last section deals with the complete process illustrated with an experimental application on a rotating machine. [Copyright &y& Elsevier]

Viscoelastic materials are widely utilized in engineering for their advantageous damping properties, which enable effective energy dissipation. They are also valued for their stiffness properties, particularly in the case of suspension design. The behavior of these materials is complex, making it challenging to accurately incorporate them into simulations. If the dependence of dynamic properties on frequency and temperature has been commonly investigated, other phenomena still need to be studied, as for instance nonlinear phenomena leading to changes with the magnitude of stress/strain. Amongst them, the Payne effect, which manifests itself by a monotonous decrease of the storage modulus, remains difficult to integrate in the simulations, and is not often characterized experimentally for vibration purposes. An approach is proposed to identify the Payne effect by combining tests derived from the Oberst beam set-up and numerical simulations. To take into account the uncertainties inherent to the experiments, the identification process is based on a Bayesian identification framework which allows to determine the parameters and their statistical properties from a limited number of experimental measurements. The coupling between the Bayesian identification of dynamic properties of a polymer sample and a digital twin of the experimental set-up allows to identify the evolution of the storage modulus as a function of the strain amplitude, as well as the confidence interval around the mean value. The application on a silicone sample confirmed the decrease of the modulus with the strain level, with a good confidence level. The methodology developed here for the specific case of the Payne effect can be extended more generally to the experimental characterization of nonlinear behavior. [ABSTRACT FROM AUTHOR]

Abstract: This paper focuses on the generalized Maxwell model (GMM) identification. The formulation of the transfer function of the GMM is defined, as well as its asymptotes. To compare identification methods of the parameters of the GMM, a test transfer function and two quality indicators are defined. Then, three graphical methods are described, the enclosing curve method, the CRONE method and an original one. But the results of graphical methods are not good enough. Thus, two optimization recursive processes are described to improve the results of graphical methods. The first one is based on an unconstrained non-linear optimization algorithm and the second one is original and allows constraining identified parameters. This new process uses the asymptotes of the modulus and the phase of the transfer function of the GMM. The result of the graphical method optimized with the new process is very accurate and fast. [Copyright &y& Elsevier]

The behaviour of dynamical systems is modified by the use of viscoelastic materials. In order to lead realistic complex eigenvalues analysis on dynamical systems, one need to model the behaviour of viscoelastic materials. The experiments show that the stiffness and the damping of such materials are frequency dependent. A large number of models often used are not able to describe this dependence; this is why the generalised Maxwell's model has been chosen. This paper describes a method based on modulus and angle curves to identify the parameters of this model. Between all the different formulations of generalized Maxwell, the pole-zero formulation is the most suited to lead the identification. However, some formulas allow to find the parameters of others formulations like the Prony one. The identification method presented here is based on the asymptotic curves of generalised Maxwell's model. This identification is led in two step, first parameters are initialised and second they are optimised. This method is confronted to others ones. If several viscoelastic materials have to be modelled in the same dynamical system, the size of the finite element model grows as quick as the number of poles. A way to reduce this size consists in constraining the poles to be equal for all materials. The method presented in this paper allows to perform the identification by taking this new constraint into account. [ABSTRACT FROM AUTHOR]

Abstract: This paper develops an experimental and numerical study of dynamic phenomena involving gear impacts with one loose gear (non-engaged gear pair) inside an automotive gearbox. A dedicated test bench was designed for this study. Signal processing tools, based on the Order Tracking Method, were specially developed in order to clarify the underlying phenomena. A particular attention was paid to the relationship between the drive shaft excitation and the energy and nature of impacts. A topological model of contact is being proposed, based on a geometric description of solids in contact. The contact between gear meshes is defined using a Single Degree of Freedom, non-linear, elastic and dissipative model. The chosen parameters of the model are not updated from measurements, but from the knowledge of the gear topology and tolerance class. Simulations, compared with experimental results, confirm the accuracy of the model proposed. Both model and experiments show, for particular excitation conditions, the emergence of repeated impacts on one side of the gear mesh. [Copyright &y& Elsevier]

In this work we present a new concept for friction damping which is based on the permanent magnetization and the flexibility of magnetoactive elastomers (MAE). The concept is called "magnetofriction" and is studied on a sandwich structure in the present work. The assembled structure consists of a MAE core and ferromagnetic skins. Due to the magnetization of the MAE, the skins are attracted to the core and the sandwich is assembled without the need of glue or other means of fixation. The magnetic forces generate the normal loading in the contact interfaces between skins and core while a tangential loading is induced by forced vibrations applied to the sandwich beam. Random and harmonic vibration tests reveal the nonlinear dynamic behavior of the sandwich structure and highlight the damping capacity of magnetofriction. The harmonic balance method is used on a nonlinear dynamic model of the system to identify the parameters related to the resonance frequency and damping ratio. The results obtained from the identification state damping ratios up to 9% under harmonic excitation, which is remarkable for friction damping. In addition, a Finite Element-based model of the structure is implemented to study the local contact states in the sandwich. Multi-physical simulations are performed to analyze the magnetic and mechanical loading in the contact interface. The local results are used to evaluate the overall contact states in the interfaces which determine the absence or presence of friction damping. The simulations show that the vibration amplitude changes the contact state. • A novel design of a functional sandwich structure for friction damping is proposed. • Distributed contact forces are established by magneto-active elastomers. • An experimental proof of concept for vibration mitigation by friction is provided. • The "backbones" of the assembled structure are identified with a nonlinear model. • A finite element based digital twin reveals the contact and friction stress fields. [ABSTRACT FROM AUTHOR]

Tuned Mass Dampers (TMD) are passive devices well-known to mitigate vibrations thanks to the principle of vibration absorption. They consist of a mass, a spring and a damper whose frequency is tuned to a critical frequency of a master structure in order to generate the expected energy transfer. As these devices require a very fine tuning to be efficient, Multi-frequency designs (Multiple Tuned Mass Dampers — MTMD) integrating several absorbers whose specific frequencies are distributed around the target resonance frequency have emerged to obtain good damping performances on a wide frequency band, even in the presence of uncertainties. The elastodynamic properties of these designs are classically estimated from lumped mass models that are a simplified representation of the 3D structures that will actually be used on a real application. In this context, the purpose of the paper is to design a metabsorber consisting in a set of 3D resonators, and to estimate numerically and experimentally the performance and the robustness in an uncertain context. The design approach relies on a dynamic analysis of the whole structure using the Finite Element Method that allows to considerate any topology for the absorbers. Epistemic uncertainties resulting from lack-of-knowledge on the target frequency are introduced, and the robustness of the metabsorber is estimated using the Info-Gap Theory that is a non-probabilistic approach for decision-making in such an uncertain context. Different frequency distributions in the metabsorber are compared to quantify the gain in performance and robustness that can be achieved changing the number of absorbers. The methodology is applied to the case of a simplified airplane model in order to control the third bending mode: numerical and experimental results show that even if the robustness improves when the number of different absorbers increases, very good results can be obtained by using a reduced number of absorbing elements in the metabsorber. • The performance and robustness of different metabsorber configurations are compared. • Numerical studies rely on the FEM method and energy quantities. • Robustness is estimated with the Info-Gap method considering lack-of-knowledge. • Numerical results are compared to experimental measurements for an airplane model. [ABSTRACT FROM AUTHOR]

• A stochastic Bouc-Wen model is presented to describe structures assembled by bolted joints. • The model parameters are identified into a Bayesian framework. • The calibration of the parameters uses analytical expression of the higher-order FRFs. • The Metropolis-Hastings algorithm is employed for approximating posterior distributions. • The Bouc-Wen model predicted hysteresis effects of the system's output for several excitation amplitudes. This paper proposes a procedure to identify a stochastic Bouc-Wen model for describing the dynamics of a structure assembled by bolted joints considering vibration data. The proposed identification approach is expressed into a Bayesian framework to take into account the data fluctuations related to uncertainties in the measurement process. The calibration of the model parameters uses the analytical expressions of the higher-order frequency response functions (FRFs) for approximating experimental measurements. The Metropolis-Hastings algorithm is employed for approximating posterior distributions. Once calibrated, the applicability of the probabilistic Bouc-Wen model is evaluated, and its dynamical behavior is compared with experimental measurements from the bolted structure. The results show that the stochastic version of the Bouc-Wen model can predict with adequate agreement, including hysteretic effects, the output of the jointed structure considering several excitation amplitudes. [ABSTRACT FROM AUTHOR]