International Journal of Engineering Science最新文献

The problem of multiple cracks originating at free surface (surface damage) in an anisotropic material is considered. We focus on the effect of material anisotropy on the mechanics of crack interactions – in particular, on the suppressing effect of interactions on crack nucleation and growth under the tensile loading (stress shielding). Importantly, this effect may change to the opposite one of enhancement, under the shear loading. These effects strongly depend on the material anisotropy. Calculations were performed for the orthotropic materials and the effect of anisotropy was examined by case studies of specific configurations that included comparison with the case of the isotropic material.

Nonlocal continuum mechanics presents still open questions about applicability of integral constitutive theories to nanostructures of current interest in Engineering Science. Nevertheless, nonlocal elasticity is widely exploited to model size effects in small-scale structures since it represents an effective tool to avoid computationally expensive procedures. The known strain-driven approach proposed by Eringen has shown an intrinsic incompatibility between constitutive and equilibrium requirements when applied to structures. Such an issue has been acknowledged by the scientific community merely for bounded continua. For structural problems defined in unbounded domains, obstruction to equilibrium caused by the strain-driven formulation is a still open issue. The present contribution definitely proves inapplicability of the strain-driven spatial convolution to structural mechanics and proposes a consistent nonlocal approach for both bounded and unbounded structures. The presented methodology is based on stress-driven spatial convolutions, representing the key paradigm to formulate a well-posed theory of integral elasticity and to effectively model scale effects in nanobeams of applicative interest in Nano-Mechanics.

The Green’s function technique has been used to directly calculate the local fields of a functionally graded material (FGM) under thermomechanical loading, thus predicting its effective material properties. For a bi-phase FGM continuously switching the particle and matrix phases, the particle size and material gradation play a complex role in its effective material behavior. Using Eshelby’s equivalent inclusion method, particles are simulated by a source of eigen-fields in a bounded bi-layered domain, while the boundary effects are evaluated by the boundary integrals of the fundamental solutions. Using the volume integral of Green’s functions, over 10,000 particles are used to simulate an FGM under thermal and mechanical loading, respectively. The dual equivalent inclusion method is used to solve for the temperature and stress fields coupled with temperature loading. The averaged thermomechanical field distribution in the gradation direction is evaluated under different loading conditions. The effective stiffness, thermal expansion coefficient, and heat conductivity significantly change with the loading condition, particle size, and material gradation. The homogenization methods, which approximate an FGM as a continuously graded material with thermoelastic properties depending on the volume fraction only, cannot capture these micromechanical features of FGMs, while the present cross-scale approach with the inclusion-based boundary element method (iBEM) directly evaluates local fields and predicts effective material behaviors with high fidelity and efficiency.

Surface instability of elastomers is of great interest in engineering science, especially in the characterization of flexible electronic materials and the manufacture of micro-nano surface topography. There is limited research on how the geometry of the block affects wrinkle appearance in a multiphysics environment. In this paper, we formulate the boundary-value problem and its incremental forms to analyze the sinusoidal surface instability of a neo-Hookean dielectric block subjected to electromechanical loads. We discover that the competition between the Maxwell stress, induced by the voltage, and the mechanical stress caused by the stretch, plays a crucial role in inducing surface wrinkling. Furthermore, we find that the aspect ratio of the block can modify the critical value of the combination of voltage and pre-stretch required for wrinkling. In addition to this, the aspect ratio also affects the shape of the wrinkling. Specifically, if the elastomer block has a smaller aspect ratio, its sinusoidal wrinkling will have a larger wavenumber. Our paper enhances the understanding of surface instability in electrostrictive elastomers and provides guidance on triggering it without breaking down the elastomer.

In this paper, we derive a dynamic surface elasticity model for the two-dimensional midsurface of a thin, three-dimensional, homogeneous, isotropic, nonlinear gradient elastic plate of thickness $h$. The resulting model is parameterized by five, conceivably measurable, physical properties of the plate, and the stored surface energy reduces to Koiter’s plate energy in a singular limiting case. The model corrects a theoretical issue found in wave propagation in thin sheets and, when combined with the author’s theory of Green elastic bodies possessing gradient elastic material boundary surfaces, removes the singularities present in fracture within traditional/classical models. Our approach diverges from previous research on thin shells and plates, which primarily concentrated on deriving elasticity theories for material surfaces from classical three-dimensional Green elasticity. This work is the first in rigorously developing a surface elasticity model based on a parent nonlinear gradient elasticity theory.

We consider the scattering of in-plane waves that interact with an edge of a structured penetrable inertial line defect contained in a triangular lattice, composed of periodically placed masses interconnected by massless elastic rods. The steady state problem for a time-harmonic excitation is converted into a vector Wiener–Hopf equation using the Fourier transform. The matrix Wiener–Hopf kernel of this equation describes the dynamic phenomena engaged in the scattering process, which includes instances where localised interfacial waves can emerge along the structured defect. This information is exploited to identify the dependency of the existence of these waves on the incident wave parameters and the properties of inertial defect. Symmetry in the structure of the scattering medium allows us to convert the vectorial problem into a pair of uncoupled scalar Wiener–Hopf equations posed along the lattice row containing the defect. The solution embodies an exact representation of the scattered field, in terms of a contour integral in the complex plane, that includes the contributions of evanescent and propagating waves. The solution reveals that in the remote lattice, the reflected and transmitted components of incident field are accompanied by dynamic modes from three symmetry classes, which include localised interfacial waves. These classes correspond to tensile modes acting transverse to the defected lattice row, shear modes that act parallel to this row, and wave modes represented as a mixture of these two responses. Benchmark finite element calculations are also provided to validate the results against our semi-analytical solution which involves, in particular, numerical computation of the contour integrals. Graphical illustrations demonstrate special dynamic responses encountered during the wave scattering process, including dynamic anisotropy, negative reflection and negative refraction.

This paper presents an investigation into the importance of micromechanical models in the analysis of forced vibrations of multi-layered microplates under a moving load. The microplate has a core fabricated from functionally graded materials and face sheets consisting of metal foam. The problem is modelled via a quasi-3D shear deformable method and the modified couple stress theory. This study assumes that the core material follows a power gradation pattern. Various micromechanical models, i.e., the Hashin-Shtrikman bounds, Voigt-Reuss-Hill, Voigt, Reuss, and Tamura, are applied to estimate the material characteristics of the core. The face sheets, composed of metal foams, possess closed- and open-cell solid porosities. System's response of time history type is determined by numerically solving the coupled motion equations obtained using a force-moment balance method. A finite element analysis is conducted for a simplified macroplate system, and the agreement between the numerical results, via the proposed theoretical approach and the theory developed in this paper, is found to be very good. The results show that the micromechanical models influence the modelled mechanical properties of the core layer, consequently impacting the numerical results for the moving-load excited response of the multi-layered microsystem.

This work presents the analytical solution to the multi-fields in the whole domain of 3D multiferroic materials with an ellipsoidal inclusion/inhomogeneity induced by eigenfields and remote loads. It is a unified approach for the fully-coupled analysis of single-phase multiferroic materials and multiferroic composite materials, which are verified by comparing with available results in the literature and finite element analysis. It is found that, inside the inclusion, the magnetic field due to the spontaneous polarization and the electric field due to the spontaneous magnetization increase monotonically with the aspect ratio of the inclusion for single-phase multiferroic materials, but they first increase and then decrease with the aspect ratio of the inclusion for multiferroic composite materials with much larger maximum magnitudes. Moreover, in the matrix of the piezoelectric-piezomagnetic heterostructure, some components of the multi-fields change dramatically with the aspect ratio of the inhomogeneity, but other components vary insignificantly. Furthermore, although the generalized strain field is usually not uniform in the matrix, the uniformity condition could be still achieved by tuning the eigenfields and remote loads even regardless of the specific shape of the ellipsoidal inhomogeneity. These results could be helpful for the design of multiferroic materials.

One of the challenges is the design of the relatively cheap Pd-free multicomponent high-temperature shape memory alloys. This paper presents the route for solving this problem by an increasing the Hf concentration in Ti–Hf–Zr–Ni–Cu–Co alloys. It was found that an increase in the Hf concentration from 23 to 32 at.% increased the transformation temperatures: A_f changed from 90 °C to 220 °C, M_s varied from 35 °C to 172 °C, while the hysteresis was constant and equal to 45–48 °C. Further increase in the Hf concentration increased the A_f temperature by 20 °C but hardly affected the M_s temperatures. Recoverable strain variation was studied on cooling under stress (in torsion mode) and heating without stress. Strain jumps were observed on γ(T) curves which were attributed to a large martensite plate appeared on cooling or disappeared on heating within large grain, which was accompanied by the abrupt strain variation. An increase in the Hf concentration decreased recoverable strain, as well as the strain up to failure. This was due to an increase in the size and volume of the brittle [Ti]₂[Ni] and [Hf]₂[Ni] precipitates. A maximum recoverable strain of 5 % was found in the alloy with 23 at.% of Hf, whereas the recoverable strain did not exceed 1 % in the alloys with 32 and 38 at.% of Hf.

There seems to be a basic misconception in several recent papers concerning the material symmetry of bodies in configurations that are pre-stressed. In this short paper we point to the source of the error and show that the material symmetry that is possible depends on the nature of the pre-stress. We also extend the results for material symmetry which have been well-known within the context of simple elastic solids to the general class of simple materials. This generalization has relevance to the material symmetry of biological solids that are viscoelastic.