International Journal of Mechanics and Materials in Design最新文献

Dynamic attenuation is a major concern in many engineering fields, and excessive energy inputs may cause fatal damages to the key devices. Therefore, there is always a demand to pursue a novel structure with the energy attenuation capacity. A metamaterial with periodic lattice-disc unit cells inspired by the tensegrity topological configuration is proposed in this study. Both theoretical and numerical modeling are conducted to examine the effects of geometrical dimensions on the bandgaps. Two types of chains are compared, including monoatomic and diatomic ones. With the increase of the number of unit cells, the dynamic attenuation effect of the bandgaps becomes prominent. This tensegrity-inspired metamaterial is 3D-printable by additive manufacturing technology. Both frequency sweep experiment and low-speed impact test are conducted. The torsional vibration mode is identified, which is decoupled with the axial vibration mode. Both improved spring-mass model and finite element model to describe the dual modes are developed to match well with the experiments. The behaviors of metamaterial bandgaps are fully verified by both numerical simulation and experiments. This study provides a novel idea for the design of additively-manufactured metamaterials for energy dissipation.

Free vibration and buckling analyses of the magneto-electro-elastic functionally graded (MEE FG) microplates in thermal environment are investigated for the first time. The MEE FG microplate is composed of two phases: piezoelectric (barium titanate) and piezomagnetic (cobalt ferrite) materials, which are distributed across the thickness direction based on the power law model. To satisfy Maxwell’s equation in the quasi-static approximation, the electric and magnetic fields are assumed a combination of trigonometric and linear functions across the plate thickness. To capture small effects on microstructures, the modified strain gradient theory (MSGT), including three length scale parameters combined with the generalized higher-order shear deformation theory (HSDT), is presented. The equilibrium equations for free vibration and buckling analyses of MEE FG microplates are derived by using Hamilton’s principle. Through those equations, the natural frequency and critical buckling load of MEE FG microplates are computed by using isogeometric analysis (IGA). Based on the Non-uniform rational B-splines (NURBs) basic functions, which achieve any desired degree of continuity of basis functions, the IGA easily satisfy the MSGT model’s higher-order derivatives. The advantage and accuracy of the proposed model are demonstrated through comparisons between the present results and those provided in the literature. The effect of the electric voltage, magnetic potential, power index, geometrical parameter and length scale parameters on the dimensionless frequencies and critical buckling loads of the MEE FG microplates is fully reported. The article’s results can be considered as benchmark solutions for the vibration and buckling of MEE FG microplates and they are helpful for manufacturing sensors, actuators, stability control, etc.

In this current study, thermoelastic static and vibration analysis of the thin functionally graded sigmoidal porous plate subjected using higher-order NURBS-based Isogeometric analysis has been performed. The variation of thermomechanical material properties of this plate is using modified power and sigmoid law. To formulate the mathematical model for plate the Kirchhoff–Love theory-based displacement fields with the virtual work principle and high-order continuity of the NURBS basis functions based isogeometric analysis are employed. Convergence and assessment study has been done to verify the effectiveness and precision of the current approach. The effect of the porosity index, material gradient index, boundary conditions, thermal loading and geometry on the deflection, vibration frequency and detailed investigation of mode shapes. From the analysis, it has been noted that normalized frequency decreases and normalized central deflection increase when the gradient index of the material rises. The findings of this analysis can be utilized for members with extremely less thickness, such as turbine plates and blades, nuclear reactor vessels, and many other machine components made of porous functionally graded material materials.

Owning a superior quality factor (Q) helps contribute to the advantages of microelectromechanical systems (MEMS) resonators due to its impact on the performance of MEMS technology-based oscillators and filters in IoTs and radio frequency applications. Anchor quality factor ((Q_{textrm{anchor}})), which measures the anchor energy loss from the MEMS resonators into their substrate, is one of the main parameters in determining Q. In this paper, a window-like phononic crystal (PnC) strip, namely W-PnC, is proposed to act as a barrier of elastic wave propagation in the support tethers of an Aluminium Nitride (ALN)-on-Silicon (Si) resonator. As a result, the resonator (Q_{textrm{anchor}}) is boosted highly. This W-PnC generates a bandgap (BG) with a width of 24.11 MHz. which covers the 152.5 MHz resonant frequency of the resonator. Three traditional support structures, including phononic crystal without hole (WH-PnC), phononic crystal with circle stub (C-PnC), and quarter wavelength (L-tether), are the counterparts of the W-PnC in the comparison of the (Q_{textrm{anchor}}) improvement. By changing the dimensional parameters of the W-PnC, the variation of the BG formation in its band structures is evaluated to provide a platform for the designers in choosing the optimal BGs. The numerical results show that (Q_{textrm{anchor}}) of the resonator with the W-PnC is superior to its counterparts. Specifically, the (Q_{textrm{anchor}}) of the resonator investigated with the two unit cell W-PnC increases 510.90%, 1771.70%, and 1048.51% over the WH-PnC, C-PnC, and L-tether, respectively. The W-PnC demonstrates its high effectiveness over other counterparts in reducing/eliminating the anchor dissipation energy source of the resonator. In addition, the BG properties of the W-PnC, such as gap width and gap location, depend on its dimensional parameters. The finite element analysis based numerical simulation method in this work is performed in COMSOL Multiphysics. The MATLAB scripts then solve the posting process of these simulations.

Strongly nonlinear structural systems exhibit high computational errors when dependability is calculated using conventional approaches such as the primary second-order method of moments and the secondary second-order method of moments. The combination of the proxy model and Monte Carlo simulation is an effective method to solve the structural failure probability problem. However, existing studies on the active learning methods of proxy models for reliability calculation mainly focus on the kriging model, while for radial basis interpolation, the existing research results are relatively few. Based on the above analysis, this paper proposes to combine the cross-validation method with multiple kernel functions to evaluate the uncertainty at the prediction points. The mathematical expression of the active learning function considering three factors is proposed: the linear combination of the distance from the surface of limit state and the uncertainty of the predicted value of the proxy model as the optimization objective function, and the distance between the sample to be selected and the initial sample point as the constraint condition. Meanwhile, using the idea of the penalty function, the constrained problem is transformed into the unconstrained problem to get the final active learning function PLF. Finally, the efficiency, accuracy, and robustness of the PRBFM method are verified by classical cases and compared with other methods. It provides a new method and a new idea for the reliability analysis of complex structures.

Harvesting vibration energy arising from the vibrating structures with ultra-low natural frequencies such as bicycle or automobile body vibrations, human body vibrations, wind turbine oscillations, etc. has always been a challenge, but could enable many potential self-powered sensing applications. To address this issue, a bistable vibro-impact dielectric elastomer generator (BVI DEG) is designed and mounted on a vibrating structure with ultra-low natural frequency to scavenge vibration energy transferred from the vibrating structure. The designed BVI DEG mainly consists of a vibro-impact (VI) DEG, two identical pre-compressed springs, two identical unstretched elastic strings, and a lightweight cuboid shell. The dynamical analysis model of the vibrating structure with the attached BVI DEG and the electrical analysis model of the BVI DEG are developed. The dynamical behaviors of the BVI DEG are numerically analyzed under the harmonic excitation and its rich dynamical behaviors including chaotic and periodic motions are revealed. The energy harvesting (EH) performance under the harmonic excitation is studied for diverse parameters, including the excitation amplitude and frequency, the natural frequency of the vibrating structure, the mass ratio, the impact distance and the different bistable potential wells. The research results show that the EH performance can be significantly improved by appropriately setting these parameters. Moreover, a further comparative study demonstrates the superiority of the BVI DEG operating in the wider excitation frequency range. This work can help guide the design of the BVI DEG mounted on the vibrating structure to enhance the EH performance of the BVI DEG.

This research investigates the feasibility of mass sensing in piezoresistive MEMS devices based on catastrophic bifurcation and sensitivity enhancement due to the orientation adjustment of the device with respect to the crystallographic orientation of the silicon wafer. The model studied is a cantilever microbeam at the end of which an electrostatically actuated tip mass is attached. The piezoresistive layers are bonded to the vicinity of the clamped end of the cantilever and the device is set to operate in the resonance regime by means of harmonic electrostatic excitation. The nonlinearities due to curvature, shortening and electrostatic excitation have been considered in the modelling process. It is shown that once the mass is deposited on the tip mass, the system undergoes a cyclic fold bifurcation in the frequency domain, which yields a sudden jump in the output voltage of the piezoresistive layers; this bifurcation is attributed to the nonlinearities governing the dynamics of the response. The partial differential equations of the motion are derived and discretized to give a finite degree of freedom model based on the Galerkin method, and the limit cycles are captured in the frequency domain by using the shooting method. The effect of the orientation of the device with respect to the crystallographic coordinates of the silicon and the effect of the orientation of the piezoresistive layers with respect to the microbeam length on the sensitivity of the device is also investigated. Thanks to the nonlinearity and the orientation adjustment of the device and piezoresistive layers, a twofold sensitivity enhancement due to the added mass was achieved. This achievement is due to the combined amplification of the sensitivity in the vicinity of the bifurcation point, which is attributed to the nonlinearity and maximizing the sensitivity by orientation adjustment of the anisotropic piezoresistive coefficients.

Nowadays, research on the application of new materials with interesting electrical properties, such as high dielectric constant, on electrostatically-actuated microstructures has become one of the prominent research fields worldwide. One of the main disadvantages of these structures is the high required voltage. The main purpose of this paper is to demonstrate the ability of dielectric materials to reduce the required voltage of capacitive MEMS and also to intensify their softening behavior. So, a nonlinear model for a capacitive microstructure has been presented and HfO₂ has been selected as the substrate material of the capacitor whose package is filled with high pressure & dielectric constant gas. It has been shown that both of these changed options together (or each of them) can significantly reduce the required actuating voltage. The physically gradient-descent-based learning method has been used to solve the governing nonlinear equation, allowing to obtain the primary and secondary resonances in the first harmony, as well as in higher harmonies of the response. It has been shown that, growing the thickness of the dielectric layer, as well as using a high coefficient dielectric gas in the package, intensifies the softening behavior.

The aim of this paper is to investigate the nonlinear static stability of nanocomposite multilayer organic solar cells (NMOSC) on elastic foundations under axial compressive loading in thermal environment. In the previous literatures, the NMOSC consists of five isotropic layers including Al, P3HT:PCBM, PEDOT:PSS, ITO and glass. However, the disadvantages of ITO are high cost, scarcity and low chemical stability. Therefore, the graphene material is chosen to replace the ITO layer in this study. The material properties of graphene layer are assumed to depend on temperature while the elastic moduli of four remaining isotropic layers are constants. For methodology, the geometrical compatibility and nonlinear equilibrium equations are derived based on the Hamilton’s principle and classical plate theory. These equations are solved by using the Galerkin method in order to obtain the expression of critical buckling load and compressive loading – deflection amplitude curves. For geometric optimization problem, three optimization algorithms including social group optimization, basic differential evolution and enhanced colliding bodies optimization algorithms are applied to find the maximum value of the critical buckling loading of NMOSC depending on four geometrical and material variables. Parametric studies are conducted to indicate the influences of temperature increment, geometrical parameters, initial imperfection and elastic foundations on the static stability characteristics of the NMOSC.