International Journal of Structural Stability and Dynamics

This paper presents the Hencky bar-chain model (HBM) for buckling and vibration analyses of Euler–Bernoulli beams with elastic end restraints. The Hencky bar-chain comprises rigid beam segments (of length a = L/n where L is the total length of beam and n the number of beam segments) connected by frictionless hinges with elastic rotational springs of stiffness EI/a where EI is the flexural rigidity of the beam. The elasticity and the mass of the beam are concentrated at the hinges with rotational springs. The key contribution of this paper lies in the modeling of the elastic end restraints of the Hencky bar-chain that will simulate the same buckling and vibration results as that furnished by the first-order central finite difference beam model (FDM) which was earlier shown to be analogous to the HBM. The establishment of such a physical discrete beam model allows one to obtain solutions for beam-like structure with repetitive cells (or elements) as well as to calibrate the Eringen's coefficient e₀ in the nonlocal beam theory that captures the small length scale effect.

In this paper, we show that two numerical methods, specifically the finite difference method and the finite element method applied to continuous beam dynamics problems, can be asymptotically investigated by some kind of enriched continuum approach (gradient elasticity or nonlocal elasticity). The analysis is restricted to the vibrations of elastic beams, and more specifically the computation of the natural frequencies for each numerical method. The analogy between the finite numerical approaches and the equivalent enriched continuum is demonstrated, using a continualization procedure, which converts the discrete numerical problem into a continuous one. It is shown that the finite element problem can be transformed into a system of finite difference equations. The convergence rate of the finite numerical approaches is quantified by an equivalent Rayleigh's quotient. We also present some exact analytical solutions for a first-order finite difference method, a higher-order finite difference method or a cubic Hermitian finite element, valid for arbitrary number of nodes or segments. The comparison between the exact numerical solution and the approximated nonlocal approaches shows the efficiency of the continualization methodology. These analogies between enriched continuum and finite numerical schemes provide a new attractive framework for potential applications of enriched continua in computational mechanics.

The problem of a half-space with cavity under vertically incident waves was solved by many researchers using different approaches. However, substantially different solutions were obtained, partially due to the difference in the method of formulation, and partially due to the lack of complete identical data for use in analysis. In this paper, the finite/infinite element approach has been adopted to study the two-dimensional response of an elastic half-space containing a buried, unlined, infinitely long cylindrical of circular shape subjected to harmonic P and SV waves. First, the analysis procedure based on the finite and infinite elements is summarized. Second, considerations in preparing the finite element mesh to ensure the accuracy and convergence of the solution are presented. Next, the validity of the procedure of solution is verified for some intuitive, fundamental cases. Finally, the problems solved by previous researchers with identical or assumed data will be re-solved, along with discussions on the discrepancies existing among the three solutions. One feature with the finite/infinite element approach is that it is simple and straightforward, involving less assumptions and mathematical operations, whose reliability has been verified in solving various soil vibration problems. The fact that the present solutions are in close agreement to those by Luco and De Barros (1994) for all the cases studied indicates that the latter is the most reliable one among the existing theories.

This paper investigates the free vibration and elastic buckling of sandwich beams with a stiff core and functionally graded carbon nanotube reinforced composite (FG-CNTRC) face sheets within the framework of Timoshenko beam theory. The material properties of FG-CNTRCs are assumed to vary in the thickness direction, and are estimated through a micromechanical model. The governing equations and boundary conditions are derived by using Hamilton's principle and discretized by employing the differential quadrature (DQ) method to obtain the natural frequency and critical buckling load of the sandwich beam. A detailed parametric study is conducted to study the effects of carbon nanotube volume fraction, core-to-face sheet thickness ratio, slenderness ratio, and end supports on the free vibration characteristics and buckling behavior of sandwich beams with FG-CNTRC face sheets. The vibration behavior of the sandwich beam under an initial axial force is also discussed. Numerical results for sandwich beams with uniformly distributed carbon nanotube-reinforced composite (UD-CNTRC) face sheets are also provided for comparison.

Metallic foam is a typical porous material with heterogeneous meso structures that affect the metallic foam's mechanical properties, in which shape irregularity of meso structures (porous cells) is the key. Shape irregularity of a porous cell reflects the deviation the cell shape from a sphere having the same volume. This paper examines the effects of meso shape irregularity of metallic foam on yield features based on three-dimensional (3D) Voronoi model and the finite element (FE) method. Three cubic foams designed by 3D Voronoi technique were constructed to furnish different statistics of shape irregularity but with the same initial density. Three normal stresses were applied on cubic metallic foam proportionally to implement the triaxial proportional loading in triaxial compression and tension. The yield surface of each 3D Voronoi foam under triaxial loading was calculated, and the influence of shape irregularity on the yield surface was investigated. The results show that the yield surface in (σ_e, σ_m) space may be depicted by an ellipse for metallic foams with different shape irregularities. The meso shape irregularity does clearly affect the yield surface with larger shape irregularity producing a smaller yield surface. This means that the metallic foam with larger shape irregularity yields more easily, and this feature is also reflected in the normalized yield surface for metallic foams with different irregularities.

Monomorph and bimorph actuators made of piezoelectric materials are widely used in smart materials and structural control. Recent studies show that their performances can be remarkably improved by the use of functionally graded piezoelectric materials (FGPMs) whose compositional profile and effective material properties are graded along the thickness direction. This paper investigates the linear and nonlinear vibration behaviors of monomorph and bimorph made from a mixture of PZT4 and PZT-5H with material composition following a power law distribution. Theoretical formulations are based on von Kármán kinematic relationships and Timoshenko beam theory to account for the effect of transverse shear deformation. The differential quadrature method (DQM) and the second-order backward difference scheme are employed to obtain the linear and nonlinear vibration frequencies. A parametric study is conducted to investigate the influences of volume fraction index, slenderness ratio, nonlinear deformation and different loading conditions.

Understanding the mechanical behaviors of graphene under different stress states is crucial to their applications. Comparing with the bucking behavior of free standing graphene under compression, the monolayer graphene embedded in the polymer matrix has a higher critical buckling load and smaller atomic length scale wavelengths as well as buckling amplitudes. In this paper, the molecular dynamics (MD) method is adopted to study the buckling behaviors of embedded graphene under uniaxial compression. Two MD models are built, namely the hybrid MD/continuum nanomechanics model and the full MD model. Periodical boundary conditions are applied in the MD simulations. Graphene sheets with different aspect ratios are considered and it is observed that the critical buckling strain of graphene sheets embedded in polymer matrix is independent of their aspect ratios. The current simulation results match well with the reported experimental results. Furthermore, it is demonstrated that the current simulation method can produce clear buckling shapes, which are difficult to observe in nanoscale experiments.

In this contribution, the finite cell method (FCM) is applied to solve transient problems of linear elastodynamics. The mathematical formulation of FCM for linear elastodynamics is presented, following from the weak formulation of the initial/boundary-value problem. Semi-discrete time integration schemes are briefly discussed, and the choice of implicit time integration is justified. A 1D benchmark problem is solved using FCM, illustrating the method's ability to solve problems of linear elastodynamics obtaining high rates of convergence. Furthermore, a numerical example of transient analysis from an industrial application is solved using FCM. The numerical results are compared to the results obtained using state-of-the-art commercial software, employing linear finite elements, in conjunction with explicit time integration. The results illustrate the potential of FCM as a powerful tool for transient analysis in elastodynamics, offering a high degree of accuracy at a moderate computational effort.

In the present paper, the geometrically nonlinear behavior of piezoelastic thin plates is studied. First, the governing equations for the electromechanically coupled problem are derived based on the von Karman–Tsien kinematic assumption. Here, the Berger approximation is extended to the coupled piezoelastic problem. The general equations are then reduced to a single nonlinear partial differential equation for the special case of simply supported polygonal edges. The nonlinear equations are approximated by using a problem-oriented Ritz Ansatz in combination with a Galerkin procedure. Based on the resulting equations the buckling and post-buckling behavior of a polygonal simply supported plate is studied in a nondimensional form, where the special geometry of the polygonal plate enters via the eigenvalues of a Helmholtz problem with Dirichlet boundary conditions. Single term as well as multi-term solutions are discussed including the effects of piezoelectric actuation and transverse force loadings upon the solution. Novel results concerning the buckling, snap through and snap buckling behavior are presented.

Structural health monitoring (SHM) of civil engineering structures based on vibration data includes three main components: ambient vibration test, modal identification and model updating. This paper discussed these three components in detail and proposes a general framework of SHM for practical application. First, a fast Bayesian modal identification method based on Fast Fourier Transform (FFT) is introduced for efficiently extracting modal parameters together with the corresponding uncertainties from ambient vibration data. A recently developed Bayesian model updating method using Markov chain Monte Carlo simulation (MCMCS) is then discussed. To illustrate the performance of the proposed modal identification and model updating methods, a scale-down transmission tower is investigated. Ambient vibration test is conducted on the target structure to obtain modal parameters. By using the measured modal parameters, model updating is carried out. The MCMC-based Bayesian model updating method can efficiently evaluate the posterior marginal PDFs of the uncertain parameters without calculating high-dimension numerical integration, which provides posterior uncertainties for the target systems.

This paper is concerned with the flexural vibration of an atomic force microscope (AFM) cantilever. The cantilever problem is formulated on the basis of the modified couple stress theory and the Timoshenko beam theory. The modified couple stress theory is a nonclassical continuum theory that includes one additional material parameter to describe the size effect. By using the Hamilton's principle, the governing equation of motion and the boundary conditions are derived for the AFM cantilevers. The equation is solved using the differential quadrature method for the natural frequencies and mode shapes. The effects of the sample surface contact stiffness, length scale parameter and location of the sensor tip on the flexural vibration characteristics of AFM cantilevers are discussed. Results show that the size effect on the frequency is significant when the thickness of the microcantilever has a similar value to the material length scale parameter.