Search

The aim of this discussion is to establish a connection between the model for sandwich beams presented in Schöftner (Acta Mech 234:2543–2560, 2023) and the so-called Krajcinovic model. Although the two models turn out to be quite similar, Krajcinovic model displays a richer kinematics and has been developed in the literature by following slightly different methodologies with respect to that adopted by Schöftner, the latter having the merit of providing equilibrium equations that allow the computation of the interfacial stresses. We also offer some remarks on the capabilities and accuracies of the models discussed. [ABSTRACT FROM AUTHOR]

This work deals with fracture mechanisms in quasi-brittle materials, focusing on the characterization of the Fracture Process Zone (FPZ) of specimens under tensile load. Particularly, paper was used as model material. Experiments were conducted on notched and unnotched specimens. Based on an image analysis of these observations, a stochastic finite element model was developed, using both a nonlocal stress-based approach and a discretized random field modeling of the Young's modulus. The proposed methodology allowed characterizing the damage zone and the size of the FPZ, analyzing the influence of the mesostructure, composed of flocs (fiber aggregates where the basis weight is larger than the average one) and antiflocs (complement of flocs). The area of the active FPZ and the normalized stress drop were linked using a surface energy dissipated in the active FPZ. The stress drop, until limiting value, increased with the width of the active FPZ. Finally, a relationship between the surface energy and the nonlocal internal length was established. [ABSTRACT FROM AUTHOR]

In recent years, electroactive paper emerged as a new alternative in the field of smart actuators. It is based on a cellulose material which is able to bend under the influence of an external electric field similarly as ionic polymer metal composites. The bending mechanism is mainly attributed to the migration of ionic charges over the thickness of a thin sheet of paper. The present contribution proposes a numerical framework for the simulation of electroactive paper. It is based on a scaled boundary plate formulation for isogeometric analysis. In contrast to the standard scaled boundary plate approach, the scaling direction is solved numerically by a B-Spline approximation. This allows to render nonlinear effects over the plate thickness as well as displacement fields of higher continuity. The model is applicable to very thin structures such as electroactive paper, and it also captures the nonlinear ionic charge distribution which is coupled to the bending mechanism of the actuator. [ABSTRACT FROM AUTHOR]

It is pointed out that the Levinson-Reddy beam theory should not be used as a higher-order model for the core, although it considers cross-sectional warping: this beam model is applicable for zero shear stress conditions at the core-skin-interfaces only, which is usually not the case for sandwich structures. The resulting sandwich beam model in [[2]] is a special solution from the Krajcinovic-Bardella derivation, which allows for richer kinematics because it considers zig-zag kinematics. Author's response to "Discussion on the paper by Schoeftner, J., "A verified analytical sandwich beam model for soft and hard cores: comparison to existing analytical models and finite element calculations", Acta Mech, 234, 2543-2560 (2023)" by Lorenzo Bardella. [Extracted from the article]

Double-roll compaction is a process to create extensible paper and paperboard suitable for replacing plastic in 3D forming applications. Understanding the macro- and micro-mechanisms governing the compaction process allows increasing the stretch potential while maintaining sufficient strength and bending stiffness. In this work, we approach the compaction process of paperboard with micro-mechanical methods featuring the unprecedented level of details otherwise inaccessible with currently available experimental tools. The loading scheme is based on experiments and continuum level simulations. The different levels of compaction and their continuous impact on the fibers' geometry, void closures, and irreversible deformation of the fibers are thoroughly characterized. We find that the structural changes are concentrated in the fibers oriented within 30 degrees of the direction of compaction. The deformation accumulates primarily in the wall of the fibers in the form of irreversible strains. The spring-back effect beyond the compaction is negligible. For the first time, the role of normal and frictional fiber-to-fiber interactions in the compaction process is investigated and quantified. The frictional interaction between the fibers has a surprisingly low impact on the outcome of the compaction process, and the normal interaction between the fibers has a dominant response. The consequence of this finding is potentially limited impact of the surface modifications targeting the friction. [ABSTRACT FROM AUTHOR]

All velocity profiles in the above paper appear to be questionable and thus may include serious numerical deviations with respect to the correct solutions. [ABSTRACT FROM AUTHOR]

In the present study, we performed comprehensive experiments and direct Navier-Stokes computations on the linear stability of gravity-driven film flows. We focused on the switching between different types of stability isles, appearing in viscous films over inclined topographies, which describes an abrupt change of the flow's free-surface stability. We systematically varied the inclination angle, the liquid, the substrate's shape and the corrugation's periodicity and uncovered when this phenomenon appears and how it proceeds. Our combined experimental and numerical work unveiled that the switching is of a universal nature as it can be induced by a slight variation of one of the multitude of completely differing parameters mentioned above. The in-depth investigation of this phenomenon presented in this article is of interest for the technical exploitation of film flows as it puts the reader into the position to avoid high-risk situations where a small change of the system's configuration leads to a significantly different system response. [ABSTRACT FROM AUTHOR]

This paper introduces the interval perturbation method into the sensitivity analysis of statistical energy analysis (SEA) models. The damping loss factors and coupling loss factors are treated as the design parameters, while the modal energy of each subsystem is considered as the decision-making target. The variation of the design parameter is characterized by an interval form, and the ratio between different interval widths is used to represent the sensitivity of the decision-making target to the design parameter. Then the sensitivity factor matrix that can help a designer find the design parameters giving the greatest benefit in noise and vibration reduction is provided. The presented interval approach is verified through simulated studies for a two-plate coupling system and a three-plate coupling system. The work of this paper can enrich and develop the theory of the sensitivity analysis of SEA models. [ABSTRACT FROM AUTHOR]

With the rapid development of lithium-ion batteries, the electrode becomes more and more miniaturized. It is necessary to analyze the stress and axial force in the nanowire electrode. The main work of this paper is to analyze the stresses and buckling in homogeneous material nanowire electrodes and two kinds of composition-gradient (positive gradient and negative gradient) material nanowire electrodes of lithium-ion batteries. Comparing the diffusion-induced stresses (DISs) and buckling in three electrodes, we analyze the advantage of composition-gradient material electrodes on DISs and axial forces. The finite deformation theory and the stress-induced diffusion hypothesis are adopted to establish the constitutive equations, and the nonlinear influence of large deformation is considered. We conclude that ratios of length to radius and constraint conditions have great influence on the buckling of nanowire electrodes. The composition-gradient materials can reduce the stress and prevent the electrode from buckling. Under the same constraint condition, the positive gradient with smaller ratio of length to radius and smaller diffusion flux can delay buckling. When the ratio of length to radius are larger and the diffusion flux is larger, the negative gradient can delay buckling. The results can provide a theoretical guidance on the way of charging operation and the design of electrodes. [ABSTRACT FROM AUTHOR]

Increasing computational power has led to the expansion of civil engineering research into using machine learning concepts for developing improved design strategies. These strategies are particularly useful for the design of extra-terrestrial habitats under uncertain environmental conditions. This paper focuses on building an unsupervised machine learning model (convolutional autoencoder) capable of detecting patterns in arch shapes and differentiating between their stress and displacement contours. Foremost, detailed discussions of the model's architecture and input data are presented. The variation of arch shapes and contours between cluster centroids in the latent space is determined, proving the capability of optimisation by moving towards clusters with optimal contours. Finally, a regression model is built to investigate the relationship between the input geometric variables and the latent space representation. We prove that the autoencoder and regression models produce arch shapes with logical structural contours given a set of input geometric variables. The results presented in this paper provide essential tools for the development of an automated design strategy capable of finding optimal arch shapes for extra-terrestrial habitats. [ABSTRACT FROM AUTHOR]

This paper deals with one-dimensional axisymmetric quasi-static coupled magnetothermoelastic problems subjected to magnetic and vapor fields. Laplace transform and finite difference methods are used to analyze the problems. Using the Laplace transform with respect to time, the general solutions of the governing equations are obtained in the transform domain. The solution is obtained by using the matrix similarity transformation and inverse Laplace transform. We obtain solutions for the temperature and thermal deformation distributions for a transient and steady state. It is demonstrated that the computational procedures established in this paper are capable of solving the generalized magnetothermoelasticity problem of a hollow cylinder with nonhomogeneous layers. [ABSTRACT FROM AUTHOR]

The present comment concerns some doubtful results included in the above paper. [ABSTRACT FROM AUTHOR]

A serious error exists in the above paper. [ABSTRACT FROM AUTHOR]

Some errors exist in the above paper. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of non-homogeneous elastic foundations on the free vibration characteristics of functionally graded graphene platelets reinforced composite plates submerged in fluid medium. A novel aspect of this study lies in exploring various distributions of the foundation, positioned either centrally within the plates or along their edges. The stiffness of the foundation is computed using Selvadurai's method, which accounts for subgrade soil properties and foundation depth. Material properties of the plates are examined by employing the rule of mixtures alongside the Halpin–Tsai micromechanical model. Hydrostatic pressure and free surface waves are not considered, given the assumption of an ideal and incompressible fluid. The theoretical framework is grounded in a novel inverse trigonometric shear deformation plate theory, where the transverse shear stress distribution is established using a newly developed inverse trigonometric function. The equations of motion are efficiently resolved through Galerkin's method. The efficacy of this approach lies in its utilization of integration to address the distribution issue of the foundation, obviating the need for deploying intricate algorithms. The proposed theory demonstrates enhanced accuracy in predicting natural frequencies compared to other published shear deformation plate theories. Moreover, this paper delves into the effect of material properties and the fluid environment on the natural frequencies of the structures. Particularly significant is our thorough investigation of the impact of variations in the locations, material properties, and sizes of the foundation on the free vibration of these plates, all of which bear great importance in structural design. [ABSTRACT FROM AUTHOR]

This paper introduces a structural design which has superior energy harvesting ability. The proposed structure is based on the ability of most periodic structures to prohibit elastic waves from propagating in a specific frequency range of the phonon band gap. By leading into acoustic black hole (ABH) units and utilizing the energy concentration characteristics of the ABH structure, the filtering effect can be made more significant. These two characteristics can produce significant strain and energy localization, which is conducive to energy harvesting. In this paper, we obtained ABH unit capable of producing broadband gaps by adjusting the geometric parameters of the ABH structure, and chose a cantilever as the research object for energy harvesting, by applying a piezoelectric patch on the unit located near the fixed end to gain a broader application in the actual situation. The results show that the beam combining the energy concentration characteristics of band gap and ABH structure has a significant improvement in energy harvesting efficiency. Optimization on the parameters of ABH unit shows that the band gap characteristic of the periodic ABH structure can further optimize the energy harvesting efficiency of practical energy harvesters, and opens up a new possibility of energy harvesting of ABH structure. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the behaviour of two symmetric mode-III collinear cracks in a functionally graded material (FGM). The fundamental goal of this paper is to provide insight on the interaction of two cracks in FGMs with the strain gradient effect. To assess the influence of gradient elasticity, we have considered two key parameters ℓ and ℓ ′ , which describe the size scale effect caused by the underlying microstructure and are related to volumetric and surface strain energy, respectively. The crack boundary value problem have been solved by the approach involving Fourier transforms and the innovative hyper-singular integro-differential equation method, where the integral equation contains the two terms in integrals for the both cracks. A system of equations has been constructed by employing the Chebyshev polynomial expansion and then by choosing the suitable collocation points the system of equation have been solved. Our investigation involves the determination of stress intensity factors at both crack tips. These factors are vital for understanding the material's fracture behavior and structural integrity. Furthermore, we explore the variations in the displacement profile when the distance between the cracks is reduced to close proximity. This particular scenario is of significant interest as it provides insights into how the interaction between the cracks impacts the overall structural response. [ABSTRACT FROM AUTHOR]

Nowadays, the dynamic behavior of rolling stocks is an essential problem. In dynamic simulation, the correct wheel-rail contact modeling is an important task. In this paper, the stiffness of the wheel-rail contact zone is found by a new, direct, and simplified formulation. This subject is developed by applying more details, such as surface roughness based on the surface topography and hardening effects of a real contact problem. These characteristics have not been considered altogether in other similar works. In this work, the contact stiffness and frequency results are obtained for different material properties and verified with analytical and experimental research. It is shown that the presented new direct method with an acceptable accuracy is easier to use than the complicated existing methods. This paper discusses the effects of contact parameter variations on contact stiffness and frequency. For example, it is shown that the contact stiffness decreases by increasing the surface roughness and increases by increasing the strain-hardening factor. [ABSTRACT FROM AUTHOR]

A matter of fact is that extremal principles have been introduced in mechanics in more (Euler, Lagrange) or less (Hamilton) than 200 years ago. One may also observe an impact of thermodynamic extremal principles based on maximum dissipation due to all the entropy production expressed in several disciplines. According fields are theory of communication, statistical mechanics and later physics of earth since already 70 years. The current paper offers some (historical) overview on several applications. "Ziegler's principle" is an implementation of the maximum entropy production going out to the dissipation and yielding a maximum dissipation. The goal of this paper is now the implementation of this extremal principle performed along an algebraic concept. Such a concept can be extended to a system with several internal variables as outlined by Coleman and Gurtin in context with the Gibbs (free) energy. [ABSTRACT FROM AUTHOR]

In this paper, the flexural wave propagation and its control of a novel piezoelectric composite pipe conveying fluid are investigated. Dual piezoelectric layers used as sensor and actuator are periodically arranged on the pipe, and a feedback amplifying circuit is applied from sensor to actuator, forming a self-powered phononic crystal (PC) control structure. The vibration reduction performance can be actively tuned by adjusting the feedback control gain instead of conventional changing the construction of pipe itself. The pipe is composed of functionally graded material (FGM), in which the material properties vary continuously along the radial direction, and a poroelastic medium is introduced. By using the Timoshenko beam theory and Hamilton's principle, a set of electromechanical coupling equations governing flexural vibration of the pipe is deduced. The band structure, band gap (BG) distribution and frequency response are presented by applying the spectral element technology. Comprehensive parametric studies are carried out. The results obtained validate the excellent vibration control effect of the proposed design, and further demonstrate the significant impacts of material, piezoelectric layers, feedback control and flowing fluid on the BG characteristics. This paper is expected to provide a technological reference for the vibration and elastic wave control of engineering composite pipe structures. [ABSTRACT FROM AUTHOR]

Compared to acoustic cloak, elastic wave cloak is difficult to construct due to inapplicability of form invariance for the control equations. Traditional elastic wave cloak is limited to Willis material or Cosserat material. In this paper, a modified symmetric design method for elastic wave cloak is proposed for underground protective structures based on a multi-center coordinate transformation scheme. First, a symmetry function is established to depict the degenerated symmetric elastic tensor by geometric averaging the elastic tensor components. The shielding performance of the symmetric method proposed in this paper is compared with that of the symmetric method in the literature. The finite element simulation results show that the symmetric cloak proposed in this paper can better reduce the displacement and shield the elastic wave. The proposed method is then used to construct elastic wave cloak for the arch shaped structure which is common in underground protective structures. A multi-center coordinate transformation scheme is applied for this purpose by dividing the arch structure into multiple coordinate transformation regions each with a local coordinate system. The shielding performance of the underground protective cloak against elastic waves with different wave incident directions and frequencies is discussed in details. The simulation results indicates that the symmetrical underground protective cloak can effectively detour the incident elastic waves, and has a good shielding effect at frequencies ranging from 50 to 1000 Hz. [ABSTRACT FROM AUTHOR]

This paper addresses the exact controllability of vibrations in a three-dimensional Cosserat elastic solid body using mathematical techniques such as operator theory and semigroup methods. The verification of exact (shape) controllability is accomplished through the application of the Hilbert Uniqueness Method, which involves investigating the boundary observability for the dual system. In partial differential equations control theory, the concept of exact observability for the dual system is fundamental to achieving exact controllability, although it differs from the common understanding of controllability. While control theory for systems governed by ordinary differential equations (ODEs) has a relatively formal and standardized approach, systems with distributed parameters, such as the Cosserat medium under consideration, involve a multitude of technical inequalities that must be established. Notably, Cosserat media possess six degrees of freedom for microstructures, in contrast to classical media with only three degrees of freedom. Consequently, exact control is required for all six variables, encompassing three translational and three rotational degrees of freedom, while classical media only necessitate the exact control of three translational variables. The paper concludes with a series of numerical studies utilizing the fast Fourier transform (FFT) and various simulations, which serve to validate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This article investigates the phenomenon of bifurcation induced by double grazing in a piecewise-smooth oscillator with a play, which is a common occurrence in many non-smooth dynamical systems namely gear systems with approval, flange contact in wheel-rail systems, and spacecraft docking. The study is carried out using a composite Poincaré mapping with bilateral constraint, which extends the local normal form mapping of one discontinuity boundary to two discontinuity boundaries. The paper first derives the local discontinuous mapping at the unilateral grazing point using the normal form of discontinuity mapping and determines the type of 3/2 singularity of the zero-time discontinuous mapping with a continuous vector field at the discontinuity boundary. The composite Poincaré mapping is then used to obtain non-classical local bifurcations caused by double grazing, including bifurcation from period-1 motion to period-2 motion, bifurcation from period-1 motion to period-3 motion, and bifurcation from period-1 motion to chaos. The results of the study are consistent with those obtained via direct numerical simulations, demonstrating the efficacy of the composite Poincaré mapping of double grazing. The paper sheds light on the behavior of non-smooth dynamical systems and provides insights into the mechanisms underlying bifurcation induced by double grazing. The findings have potential applications in various fields including engineering, physics, and biology. [ABSTRACT FROM AUTHOR]

In this paper a selected type of elasto-viscoplastic constitutive equations is considered. The viscoplastic model which was proposed by Marquis is generalized by allowing multiple terms describing the isotropic and the kinematic hardening. Furthermore, the presented model formulation enables one to use an arbitrary equivalent plastic strain function to describe the isotropic hardening behavior. What is more, the backstress evolution equation which was proposed by Marquis was modified so that any equivalent plastic strain function can be used in the recovery term now. The general form of the generalized constitutive model obtained this way was subsequently implemented into the finite element method (FEM). For that purpose, the radial-return mapping algorithm was utilized. The consistent tangent operator was derived for the considered class of models and is presented in the paper. A developed user material subroutine (UMAT) which allows one to use the viscoplastic models under consideration in the FEM program CalculiX is attached in the appendix section. A number of numerical simulations were conducted in order to verify the performance of the developed UMAT code. [ABSTRACT FROM AUTHOR]

In this paper, the forced vibration of a functionally porous sandwich beam with a viscoelastic core has been investigated. The upper and lower layers of the beam are made of functionally porous materials, and the porosity gradient in porous layers is distributed through their thickness. The core of the beam is made of viscoelastic materials. The Golla–Hughes–McTavish (GHM) model is employed to simulate the viscoelastic behavior of the core. Applying the Hamilton principle and Euler–Bernoulli theory, the governing equation of motion is obtained for a simply supported beam. The Newmark method is applied to solve the time-dependent differential equation of the beam. The results are compared with data from the literature review and a commercial finite element software. In the Results and Discussion section of the paper, a parametric study is performed to investigate the effects of porosity and viscoelastic parameters on the forced vibration of the beam. Finally, the results obtained by the GHM model are compared with the Kelvin–Voigt model for constant and variable input frequencies. According to the results, both models predict identical behavior for constant input frequency. However, the GHM model provides better results for the case of variable input frequency. [ABSTRACT FROM AUTHOR]

Stresses are generated in plates under initial loads, which couple with the subsequent transverse deformation to affect the buckling and transverse vibration characteristics of plates. There exists no exact solution method for the stress field of a rectangular plate under arbitrary in-plane loads. In this paper, the stress field of a rectangular plate under arbitrary in-plane loads is solved based on the principle of minimum potential energy. The stress function is decomposed into homogeneous and special solutions. The homogeneous solution is represented by the Chebyshev polynomial while the special solution is expanded by the Fourier series. Then, the Ritz method is used to analyze the transverse vibration and buckling characteristics of the rectangular plate. The product of the boundary function and Chebyshev polynomial is used to build the vibration mode function. The present results are verified by comparing to existing studies and those obtained from finite element method (FEM). The effects of the magnitude and distribution of in-plane boundary stresses and boundary conditions on the dynamic characteristics and stability of the rectangular plate are analyzed. The method used in the paper has demonstrated improved convergence and accuracy with good universality. [ABSTRACT FROM AUTHOR]

The fundamental equations and some special solutions of contact mechanics for solid fractal surfaces are proposed in this paper. Firstly, as for fractal solid surface, the probability distribution equation of height without pressure, the probability distribution equation of vertical displacement with pressure and the probability distribution equation of contact stress are established. Secondly, considering the adhesion force, a special solution is given for the probability distribution equation of contact stress when the fractal index is 2. Finally, when the area ratio of multi-scale contact is 0.5, the influence of different derivative orders on the results is discussed. In this paper, a complete analytical framework is given for the static multi-scale contact mechanics. [ABSTRACT FROM AUTHOR]

This paper presents a forced vibration analysis of open doubly curved sandwich panels subjected to a moving constant force. In this paper, the effect of softness of the core is considered by implementing a semi-layerwise theory. To this aim, the first-order shear deformation theory is adopted for the face sheets and a higher-order theory which was obtained based on 3D elasticity theory is considered for the core. The presented formulation is general and as the deepness parameter is accounted in the strain–displacement relations, the formulation can be used for a wide range of deep as well as shallow doubly curved shells. To obtain the dynamic response of the system, the finite element method (FEM) along with the Newmark method is used. The proposed element is a higher-order one with nine nodes and each node has fifteen degrees of freedom. The effect of various parameters such as length-to-thickness ratio, in-plane aspect ratio, boundary conditions, lamination scheme, and fiber orientation angles on the dynamic response of the structure is examined. Additionally, the critical velocity of the force at which the structure experiences maximum dynamic deflection is obtained in each case. The results show that as the length-to-thickness ratio of the structure increases, the dynamic magnification factor curve increases with respect to non-dimensional velocity. This study provides insights into the dynamic behavior of doubly curved sandwich panels with soft cores and can aid in the design of such structures for specific applications. The results of this study can also serve as a benchmark for future studies on the forced vibration behavior of doubly curved sandwich panels. [ABSTRACT FROM AUTHOR]

Dynamic reliability evaluation of large-scale reinforced concrete (RC) structures is one of the most challenging problems in engineering practices. Although extensive endeavors have been devoted to mechanical analysis of concrete structures in the past decades, it was recognized that the randomness from both structural parameters and excitations have significant effects on the dynamic behaviors of structures with complex nonlinearity, damage, energy dissipation, and plasticity. Thus, great difficulty exists in evaluating the nonlinear stochastic responses and dynamic reliability of the real-world complex structures of large degrees of freedom. In the present paper, a physically driven method for refined probabilistic response and seismic reliability evaluation of real-world RC structures is proposed via synthesis of the refined mechanical analysis and the physically-based uncertainty propagation. In this method, the material parameters can be treated as probabilistically dependent random variables characterized by vine copulas, and the ground motion is modeled by non-stationary Clough–Penzien spectrum. The uncertainty propagation of arbitrary response quantity(-ies) of interest is governed by the dimension-reduced probability density evolution equation (DR-PDEE). The intrinsic drift coefficients in the DR-PDEE are the physically driven force for the uncertainty propagation and can be identified via data from representative dynamic analyses of the structure. The time-variant reliability of the structures can be captured by solving the physically driven DR-PDEE, which cannot be achieved by the general Monte Carlo simulation (MCS) due to the prohabitively large computational cost. Finally, a practical engineering application is shown in this paper for the probabilistic response and seismic reliability evaluation of a 24-story RC shear wall structure with nearly 280,000 degrees of freedom (DOFs). [ABSTRACT FROM AUTHOR]

In this paper, a dynamic interaction model of the coupled system of railway bridge, foundation, subsoil, ballast, track, and high-speed train is presented, with special emphasis on the longitudinal interaction between the track and the bridge structure, taking into account the flexibility of the ballast. After a description of the model of this interaction system, the equations of motion are given separately for each subsystem. The discretization of the bedded rails is performed by two different approaches. In the first approach, the deflection of the rails is expanded into the eigenfunctions of a finitely long bedded beam representing the rails. In the second, simplified approach, the track response is represented by a superposition of the static deflection of the infinitely long bedded beam due to a concentrated load. The coupling of the bridge structure with the track is achieved by a component mode synthesis technique, which in the first approach leads to a representation of the equations of motion in state-space. A discrete substructure technique is used to couple this subsystem with the train model. The two presented strategies are verified by comparison with results of a finite element model of this interaction system. Several application examples reveal the influence of the horizontal track–bridge interaction and other modeling parameters on the dynamic bridge response. [ABSTRACT FROM AUTHOR]

In structural dynamics, response modeling relies on parameters, which are to be identified by experiments. However, for satisfactory results, the design of such experiments is laborious and requires a comprehensive physical insight, which is limited. Furthermore, accurate models are high dimensional and can operate only with a large set of parameters, which increases the experimental effort even more. Efficient data sampling methods have been addressed in studies within areas of design of experiments and active learning. However, generating a data set for nonlinear dynamic systems poses an increased degree of difficulty, since the system needs to be guided through unknown dynamics to collect the desired data points. In this paper, we address this challenge by introducing a theoretical data generation framework for testing-integrated modeling. In the proposed framework, we use feedforward neural networks (FNNs) for inverse modeling of the nonlinear restoring force of the systems. By sequentially evaluating the accuracy of the trained model on a given test data set, the excitation signal applied on the system is adapted to generate optimal response data which allow the FNN model to learn the restoring force behavior. Hence, data generation is posed as an optimization problem and pattern search algorithm is used for sampling. The performance of the proposed framework is evaluated, and it is shown that it outperforms unsupervised sampling methods. [ABSTRACT FROM AUTHOR]

The indirect approaches based on the responses of specially designed moving vehicles on bridges to extract bridge dynamic properties have received great research attention. Wavelet transform (WT) is shown to be a useful tool for the analysis of vehicle responses and bridge damage detection in the vehicle-bridge interaction system. However, past studies have demonstrated that road surface roughness poses difficulty in applying wavelet analysis to successfully detect bridge damage. In this paper, a two-step method is proposed for bridge damage detection based on WT analysis of the residual contact response of the front and rear vehicle wheels of a four degrees of freedom (4-DOF) moving vehicle to reduce the influence of road surface roughness. In the first step, the generalized Kalman filter under unknown input (GKF-UI) developed by the authors is used to identify the unknown contact forces and the state vector of the vehicle. Due to the advantages of GKF-UI, acceleration and displacement sensors can be installed conveniently on the vehicle body instead of on the wheel axles in previous studies. Then, the contact-point bridge deflection responses of the front and rear vehicle wheels are estimated from the identified contact force and vehicle state. In the second step, the residual contact-point bridge deflection response is obtained by subtracting the front contact-point bridge deflection and rear contact-point bridge deflection with a time shift to reduce the influence of road surface roughness. Then, the locations of bridge damage can be identified based on WT of the singularities of residual contact-point bridge deflection response. Numerical examples of bridge damage detection demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The identification of frequency zones where waves propagate freely (i.e., propagation zones) and where they are attenuated (i.e., attenuation zones) in a railway track, plays an important role in a number of applications, such as nondestructive testing, structure-borne noise prediction, and vibration control. This paper presents a numerical model based on the wave finite element method to study wave propagation and attenuation in periodic supported rails. The model involves postprocessing of element matrices of a rail span (i.e., rail segment between two supports), which is modeled using three-dimensional finite elements meshed through the cross section. The model uses solid elements to capture the complex cross-sectional deformation of the waves and considers the dimensions of the periodic supports. In order to obtain accurate results, the stiffness and the damping coefficients of the supports are calibrated through a finite element model updating procedure that utilizes the modal parameters and the attenuation coefficients obtained from experiments. The results demonstrate that the proposed model is capable of (i) capturing the classic vibrational modes (i.e., vertical and lateral bending), (ii) describing the complex cross-sectional deformation and the mode conversions, and (iii) obtaining the wave propagation and attenuation regions of periodic supported rails. [ABSTRACT FROM AUTHOR]

The scope of this paper is to apply a model-correction-based strategy for efficient reliability analysis of uncertain dynamical systems based on a low-fidelity (LF) model whose outcomes are corrected in a probabilistic sense to represent the more realistic outcomes of a high-fidelity (HF) model. In the model-correction approach utilized, the LF model is calibrated to the HF model close to the so-called most probable point in standard normal space, which allows a more realistic assessment of the considered complex dynamical system. Since only few expensive limit state function evaluations of the HF model are required, an efficient reliability analysis is enabled. In an application example, the LF model describes an existing single-span railway bridge modelled as simply supported Euler–Bernoulli beam subjected to moving single forces representing the axle loads of a moving train. The HF modelling approach accounts for the bridge–train interaction by modelling the passing train as mass-spring-damper system, however increasing the computational effort of the limit state function evaluations. Failure probabilities evaluated with the model-correction approach are contrasted and discussed with failure probabilities of the sophisticated bridge–train interaction model evaluated with the first-order reliability method (FORM). It is demonstrated that the efficiency of the method depends on the correlation between the LF and the HF model. A comparison of the results of FORM and the model-correction-based approach shows that the latter provides reliable failure probability prediction of the HF model while leading to a significant reduction in computational effort. [ABSTRACT FROM AUTHOR]

The paper presents a semi-analytical method, named the Double Legendre Polynomial Method (DLPM), which is extended for modeling the axisymmetric free vibration of a functionally graded piezoelectric (FGP) hollow cylinder resonator. The FGP resonator is composed of two-phase graded piezoelectric materials, Lead zirconate titanate (PZT4) and aluminum nitrid (AlN), on the top and bottom surfaces, respectively, where the material properties gradually change along the thickness direction. The integration of FGP materials with piezoelectric materials is an innovative aspect in material science, and this paper explores their dynamic behavior, providing insights into their mechanical and electrical properties and contributes to expand our understanding of the axisymmetric free vibration of FGP hollow cylinder resonators as a crucial factor for optimizing their performance across a wide range of applications, including sensors, actuators, energy harvesting, and structural health monitoring systems. The DLPM is applied to solve the wave governing differential equations of motion, offering a new tool for studying the dynamic behavior of FGP hollow cylinders under axisymmetric vibration. The study investigates the effects of the diameter-thickness ratio on the effective electromechanical coupling coefficient and the resonant and anti-resonant frequencies of the FGP hollow cylinder. The results show that as the diameter-thickness ratio increases, the frequency-diameter product appears to become more stable. This observation is a valuable insight for optimizing the design of these resonators. Furthermore, the study presents the electrical input admittance, the natural frequencies as well as the mechanical displacement and electric potential profiles of the resonator. All the provided results are based on the calculation of the resonant frequencies. The validity of the presented results was verified by the comparison with the existing ones reported in the literature. [ABSTRACT FROM AUTHOR]

The geometry description plays a central role in many engineering applications and directly influences the quality of the computer simulation results. The geometry of a space curve can be completely defined in terms of two parameters: the horizontal and vertical curvatures, or equivalently, the curve curvature and torsion. In this paper, distinction is made between the track angle and space-curve bank angle, referred to in this paper as the Frenet bank angle. In railroad vehicle systems, the track bank angle measures the track super-elevation required to define a balance speed and achieve a safe vehicle operation. The formulation of the track space-curve differential equations in terms of Euler angles, however, shows the dependence of the Frenet bank angle on two independent parameters, often used as inputs in the definition of the track geometry. This paper develops the general differential equations that govern the track geometry using the Euler angle sequence adopted in practice. It is shown by an example that a curve can be twisted and vertically elevated but not super-elevated while maintaining a constant vertical-development angle. The continuity conditions at the track segment transitions are also examined. As discussed in the paper, imposing curvature continuity does not ensure continuity of the tangent vectors at the curve/spiral intersection. Several curve geometries that include planar and helix curves are used to explain some of the fundamental issues addressed in this study. [ABSTRACT FROM AUTHOR]

In this paper, a modified time–frequency transform method is proposed by introducing a modified factor based on elastic wave theory and classical Fourier transform. The feasibility of the proposed method is verified by taking the front semi-cylindrical canyon and hill topography subject to horizontal anti-plane shear waves as the research object. Based on the analytical solution of wave field in frequency domain and modified time–frequency transform method, the modified wave field in time domain and the amplitude of surface displacement are obtained, and the wave effect of the front terrain is discussed. The results show that the wave effect of front canyon is stronger than that of the hill, and the range is wider that cannot be ignored under thousands of characteristic radii. The results and the proposed modified time–frequency transform method can provide theoretical reference and a new idea for earthquake engineering. [ABSTRACT FROM AUTHOR]

Lattice materials possess excellent mechanical properties such as light weight, high specific stiffness and high energy absorption capacity. However, the commonly used lattice materials inspired by Bravais lattice often give rise to property anisotropy that is not desirable for engineering application such as bone implants. For this sake, a design methodology for isotropic stiffness is proposed in this paper. Firstly, an efficient theoretical method for calculating the elastic matrices of lattice materials was presented. The method is based on Euler–Bernoulli beam theory and the assumption of affine deformation of cell vertices applicable to cubic truss-lattice materials. The theoretical approach was validated by comparing with the finite element simulations. Utilizing the validated theoretical method, and by properly combining the lattice configurations with complementary stiffness along different directions, an elastic isotropic lattice material can be obtained. A few examples are presented to demonstrate the effectiveness and adaptability of the proposed design strategy by permutating the combinations of different classic lattices. The method proposed in this paper can provide a new approach in the design of lattice materials with excellent anisotropy control. [ABSTRACT FROM AUTHOR]

The most common coated structure contact problems include spherical, conical and cylindrical contact. The evaluation of mechanical performance for coating structures has always been a very important issue in the field of mechanics and materials; due to the too small proportion between the thickness of the coating and the substrate, the deviation of traditional evaluation methods becomes unacceptable. Indentation technology is the basis for analysis, measurement, and the standardized application of coating structures. The research object of this paper is cylindrical contact, which is one part of building the theoretical framework of contact mechanics of coating structures. In the paper, an accurate and efficient general theory of the frictional cylindrical contact problem for the coated structure is presented. The general solutions are expressed in the form of harmonic functions. 3D exact solutions of a transversely isotropic elasticity coated structure under frictional cylindrical punch contact are derived, based on the general solution and the boundary conditions. The theory is proposed in two cases, including the frictionless contact and the frictional contact. By contrast with existing theories (obtained in this paper by degradation), the numerical calculations show the good convergence, high accuracy, efficiency, and stability. The difference of stress singularity analysis between Finite Element Method (FEM) and the presented theory is explained, which shows the theory's validity and applicability. This analytical theory plays an important role in boundary stress singularity analysis. The finite element comparison shows that the analytical theory plays an important role in boundary stress singularity analysis and further, proves the validity and applicability of this theory. In the numerical analysis, the influence of coating thickness on interface stress is shown, the distribution forms of stress and displacement are given, and the influence of material parameters and coating thickness on interface failure is investigated. The analytical expressions are presented with the elementary functions. In the era of highly developed computer intelligence, the presented theory will be the basis of the interface failure problem analysis and material parameters' determination, also for future use deep learning to solve the problem of contact mechanics provides the basis of large precise sample. [ABSTRACT FROM AUTHOR]

In this paper, an exact elasticity solution of functionally graded material (FGM) rectangular plate under cylindrical bending is presented. The formulation is based on the displacement approach in which 3D elasticity equations are reduced to 2-D equations using plane-strain conditions. In the present formulation, an exact elasticity solution is feasible due to the consideration of simply supported boundary conditions with applied loads expressed in harmonic forms. Functionally graded material (FGM) infinite rectangular plate subjected to realistic transverse normal loads are analyzed. Solutions have been presented for FGM plate with various aspect ratios and gradation factors. Variation of displacements and stresses through the thickness has been investigated for the FGM plate subjected to single sinusoidal load, uniformly distributed load, hydrostatic load, and strip load. Validation of results is presented using reference results in the literature. The extensive results presented in this paper can be served as benchmark solutions for the assessment of improved plate theories. [ABSTRACT FROM AUTHOR]

Interference fit is a classic issue in mechanical engineering. In this paper, under the axial/spherical symmetrical assumption, the analytical solutions for the interference fit problem of the internal and external functionally graded materials (FGMs) hollow cylinder/spherical shell are obtained. Herein, the unified form of the FGMs hollow cylinder/spherical shell basic equation is given by introducing a geometric parameter. The degradations of the analytical solutions in this paper are consistent with the corresponding results in the existing work. The effects of interference value, structural material parameters, and geometric dimensions on the displacement and stress distribution of FGMs structures are analyzed numerically. [ABSTRACT FROM AUTHOR]

In this paper, an equivalent imperfect interface model of PN homojunction/ heterojunction of piezoelectric semiconductor for the multi-field coupled wave propagation is proposed firstly. PN junction is a special structure formed by the contact of two different types of doped semiconductors, which has been used extensively in semiconductor devices. Due to the gradient distribution of the electric potential and carrier concentration in PN junction of finite thickness, the reflection and the transmission will arise when the coupled waves propagate through PN junction. The effects of the PN junction on the wave propagation will be much more complicated by the accurate estimation. An equivalent imperfect interface model without thickness but with seven interface parameters is established to simulate the effects of PN junction which largely reduces the calculation cost. The numerical examples are provided and compared with the state transfer matrix method and the piecewise homogenization method. Energy flux of the reflected and transmitted waves are estimated, and the energy conservation is checked to verify reliability of the numerical results. [ABSTRACT FROM AUTHOR]

Pore defects are common defects in composites and can seriously affect the mechanical properties of composites. The present paper not only considers the pore defects, but also considers the influence of interface defects on the effective stiffness of 3D braided composites. A damage model is developed to predict the damage propagation of 3D braided composites considering pore defects. A multiscale simulation method using representative volume elements (RVE) combined with a micromechanical method and the finite element method is developed in this paper to meet the multiscale and periodic characteristics of 3D braided composites. The constituents at the microscale are composed of matrix, interface, fiber and pores, and the constituents at the mesoscale are composed of matrix, yarns and pores. The yarn at the microscale is homogenized by means of Mori–Tanaka model and extended double-inclusion model. The prediction and analysis methods of the existing models are compared with the experimental results to prove the effectiveness of the method. [ABSTRACT FROM AUTHOR]

This paper presents thermodynamic characteristics of functionally graded (FG) doubly-curved panels with varying circumferential size. The circumferential size considered in this paper means the circumferential rotating angle and varies according to certain rules in the longitudinal direction. The theoretical formulation is derived by using Hamilton's principle in conjunction with first-order shear deformation theory and the displacement and rotating components of the FG doubly-curved panels with varying circumferential size are described approximatively by employing meshfree Tchebychev point interpolation (TPIM) shape function. The thermal effects on the natural frequency of FG doubly-curved panels are studied by employing the thermo-elastic theory. For forced vibration analysis, rectangular and exponential pulse are considered. The convergence of the established theoretical modeling is verified by convergence studies, the validation of the established theoretical modeling is confirmed through comparison with the results of published literature and finite element method. In numerical example, the influences of geometry dimension, boundary conditions, thermal and external loads on the thermo-dynamic characteristics of FG doubly-curved panels with varying circumferential size are investigated systematically. The research results show that the established numerical model has converged basically when the number of node points is greater than Nx = 11 and the boundary spring stiffness increases by more than 1012; the maximum error of comparison results is less than 1%; the boundary conditions, power-law index p, starting angles φ0, temperature and starting circumference A have important influence on the thermodynamic response including free and forced vibration characteristics of FG doubly-curved panels with varying circumferential size. [ABSTRACT FROM AUTHOR]

High-strength steel (HSS) columns are widely used in industry and construction because of their outstanding properties. Predicting the ultimate bearing capacity of HSS columns is not an easy task due to many nonlinear factors such as geometry and material properties. In this paper, a Cluster and Search Stacking Algorithm (CSSA) model based on the cluster algorithm, search algorithm, and Stacking algorithm is proposed to predict the ultimate bearing capacity of HSS columns. Specifically, the clustering algorithm is used to cluster the base models, and the search algorithm is implemented to find the best combination of base models in the Stacking algorithm. Results show that the proposed CSSA model is more effective than base models optimized by the Bayesian Optimization algorithm. Furthermore, the Bland–Altman approach is utilized to examine the consistency of the CSSA model to validate its reliability. Finally, the Shapley additive explanation (SHAP) method is introduced to analyze and explain the ultimate bearing capacity predicted by the CSSA model. [ABSTRACT FROM AUTHOR]

In this paper, the influence of the surface effect on wave propagation characteristics in functionally graded metal foam plates (FGMFPs) with nanopores is studied, where different porosity distribution patterns are taken in account. The surface effect between pore and matrix in FGMFP is considered by the Gurtin–Murdoch surface elasticity model. The plate is divided into finite thickness layers along the gradient, and each layer of porous material is homogenized using locally exact homogenization theory. On the basis of obtaining the effective modulus of each layer of porous material, the governing equations of the plates are obtained by Hamilton's principle and different plate theories, upon which wave dispersion and phase velocity curves of FGMFP are obtained. The developed method is verified by comparing the wave dispersion curves against existing literature. Finally, the effects of different plate theories, porosity distribution, unit cell array, surface effect, pore radius and its distribution pattern, and graphene platelet weight fraction on the wave dispersion and phase velocity curves are systematically investigated. The results in this paper may provide guidance for the design of FGMFPs with nanopores. [ABSTRACT FROM AUTHOR]