European Journal of Mechanics A-Solids最新文献

Open-cell nickel foam (OCNF) is a highly porous, three-dimensional material with potential applications in various fields, such as energy storage, catalysis, and thermal management. However, the microstructural effect of pores per inch (PPI), cell size and strain rate (SR) sensitivity on the mechanical properties of OCNF has not been fully explored. We characterized the samples of OCNFs using digital image correlation (DIC), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) mapping. Our results show that the OCNF exhibits a linear elastic response under quasi-static compression, with high compressive strength and a low compressive modulus. The dynamic compression test results demonstrate that the OCNF has a high energy absorption capacity and good structural stability. We designed and constructed a method to generate the 3D meshes based on the scans of the OCNFs obtained by X-ray micro-CT. The 3D meshes allow the finite element method to capture the key features of the mechanical behaviors with high fidelity. The simulated mechanical behavior of the OCNFs demonstrates strong concordance with the observed experimental findings.

This paper deals with the development of constitutive equations to model the mechanical behaviour of compressible elastomers. These materials are naturally incompressible but can be made compressible by the addition of hollow microspheres, for example. Such a material is referred to as syntactic foam. The CEA (French Commission for Atomic and Alternative Energies) employs such compressible materials as seals in complex structures to reduce the internal stresses in vulnerable components and prevent their failure. The behaviour of these structures is predicted by finite element simulations. It is important to know and model the mechanical behaviour of the seals. Like elastomers, they can undergo large deformations. The microspheres enable the material to undergo large volume change unlike pure elastomer that is nearly incompressible. This compressibility also intensifies dissipative phenomena encountered in elastomers such as viscosity or plasticity. Furthermore, the Mullins stress softening effect is also intensified even for loadings that only bring about volumetric changes. To model these behaviours, a phenomenological approach was developed based on the isochoric/volumetric decomposition of the deformation gradient. The method of intermediate dissipative configurations was employed to introduce multiple phenomena, including viscosity (with several characteristic times) and viscoplasticity, for these two parts of the deformation. The constitutive equations and their flow rules were implemented in Abaqus through a UMAT subroutine and using a numerical approach to define the tangent operator. The parameters of the behaviour law were identified using a model reduction technique known as shape manifold approach. The resulting model can be compared with experimental data.

This study explores energy harvesting from beam vibrations induced by the passage of various masses, including concentrated, distributed, unbalanced, and consecutive masses. The energy harvester incorporates an arc-shaped auxetic substrate with a re-entrant, missing rib, and double-arrowhead structure. The system is simulated under different base excitations due to harmonic excitation and a bridge-simulator midpoint vibration. The first part involves theoretical analysis and finite element (FE) simulation of moving masses on a beam. In the second part, a theoretical examination and FE simulation of cantilever piezoelectric energy harvesters with arc-shaped auxetic substrates are conducted. Theoretical relations for the Euler-Bernoulli (EB) beam are derived using the Wentzel-Kramers-Brillouin (WKB) method. The study reports a maximum output power of $1.29\mu W$ at an optimal resistance of $0.148M\Omega$ under bridge excitation with the passage of a distributed mass.

In a previous study from the author and his co-worker, a constitutive model for isotropic, elastic perfectly-plastic materials was developed using scalar, conjugate, stress/strain base pairs. These stress/strain base pairs result from a Gram–Schmidt decomposition of the deformation gradient. A limitation of this prior work is that we assumed the microscopic structures of such elastic–plastic materials would remain constant throughout a deformation process, i.e., there would be no change in the resulting microstructural properties. Typically, internal state variables are used to represent macroscopic manifestations of these microstructural properties. In this paper, we incorporate internal state variables into our previously developed constitutive model, and as a consequence, plastically-induced anisotropy shows up naturally in the developed model. These are, however, different from the typically used internal state variables and are introduced only for this purpose.

Both experimental and numerical evidence supports that blending grains of different sizes within a polycrystalline materials allows to increase the alloy strength while maintaining its ductility. Microstructure-based modeling approaches have been developed to uncover the mechanisms governing the strength–ductility synergy, thereby assisting in the strategic design of alloys with multimodal grain size distributions. Due to significant differences in grain size and the need for statistical representativity, many approaches resort to simplifying hypotheses regarding the transition from ultrafine to macroscopic scales. Although the limitations of these simplifications in unimodal polycrystals are well documented, their biases associated with the micromechanical analysis of multimodal systems have not been addressed. To tackle this general question, this paper considers the model problem of a bimodal polycrystal with a single coarse grain embedded in a matrix of ultrafine grains. To ensure unbiased representation and enable systematic multi-scale comparisons, the analyses are based on a unimodal ultrafine grain polycrystal and its paired bimodal polycrystal, both of which have an identical microstructure of ultrafine grains. In order to distinguish structural effects of a classical matrix inclusion problem from crystal related interactions, two types of constitutive behavior have been investigated, both in 2D and 3D: isotropic macro-homogeneous for each grain population or full-field crystal plasticity. The four related configurations of a bimodal polycrystal all share the same macro-scale constitutive behavior. The distortions introduced by each of the above simplifying hypothesis and their combinations have thus been comprehensively evaluated, paying a particular attention to the specific patterns of localization of stress, strain and plastic activity. The 2D approach has been confirmed to be efficient in describing characteristic interaction mechanisms, yet with a propensity to accentuate localization phenomena. However the volume fraction of the coarse grain to achieve a given macro-scale stress–strain behavior has been found to be different from that in 3D.

Honeycomb crash absorbers are known as mechanical energy-absorbing systems in both automotive and aerospace industries. However, the gap of knowledge in the transverse impacts of multi-foam-filled or stiffener-reinforced honeycombs is still unfilled. This paper investigates the energy absorption process in large crash boxes applied onto a road maintenance vehicle, exploring four aluminium honeycomb absorbers with design factors like added aluminium foam, corrugated sheet thicknesses, and stiffener reinforcements. The optimised foam-filled honeycomb structures are analysed for four crash scenarios in two different directions; frontal impact (T-direction) and lateral impact (L-direction) subjected to 50 km/h crash speed. The objective of this research is to identify the most efficient design that achieves a maximum acceleration of up to 20g while absorbing a specific energy of 145 kJ. The FE models were developed in ABAQUS to explore various scenarios related to damage zones, impact energy capabilities, and multi-foam-filled crash boxes. Finally, the lightest design of honeycomb absorbers which can maximise energy absorption while maintaining acceleration below the specified threshold of 20g will be recommended.

Non-pneumatic tires (NPTs) fundamentally avoid the risk of tire blowout of traditional pneumatic tires, but the overall and key component performance inevitably degrades due to factors such as high temperature, variable load, variable working conditions and impact in its service process. Once this leads to failure, it will significantly impact on vehicle safety. To this end, this paper studied the influence of local structural damage on the dynamic response of NPTs, which lays the foundation for realizing health monitoring of intelligent non-pneumatic tires (INPTs). Firstly, a three-dimensional nonlinear finite element model of NPTs was established, and the failure locations of NPTs were determined by fracture mechanics and maximum strain energy density; Secondly, the influence of structural damage on the static and dynamic performance of NPTs was analyzed; Finally, the sensitivity of the acceleration signal and sensor position of the tire inner liner to the local structural damage was studied. The research results show that structural damage will cause the stress of the spokes and shear layer to increase, and as the number of broken spokes increases, the shear layer will bear a larger load. Compared with the circumferential and lateral acceleration, the radial acceleration has the highest sensitivity to the damage of NPTs. The sensor closest to the damage location is the most sensitive to the damage. The research results provide a reference for the structural optimization design and health monitoring of INPTs.

Bistable structures with the elastic instability caused by buckling are confirmed to perform significantly in micro-electromechanical systems, metamaterials, energy harvester, vibration isolation and morphing structures. The target of this paper is to explore the dynamic responses of cross-ply bistable composite laminate, focusing on the nonlinear effect of the single- and double-well vibration. Both theoretical and finite element (FE) methods are employed to simulate the nonlinear vibration and dynamic snap-through of bistable composite laminate under the foundation excitation at the center. In the theoretical model, the governing equations are established via Lagrange's equation based on the first-order shear deformation theory, von Karman nonlinear strain-displacement relation and Rayleigh-Ritz method. The fourth-order Runge-Kutta method is adopted to solve the governing equations, and the numerical results are validated by FE model. Subsequently, the details of the dynamic responses are analyzed to identify the nonlinear effects in the form of bifurcation diagram, phase portrait, time history, Poincare maps and amplitude spectrum. The dynamic responses are examined for a series of excitation parameters in both time and frequency domain. Through fixed frequency and frequency sweep tests, the nonlinear phenomenon of the single- and double-well vibrations are analyzed including superharmonic resonance, stiffness softening, hysteresis phenomenon, various periodic and chaotic vibration. The diverse responses to external inputs contribute significantly to efficiently predicting mechanical behaviors in real-world conditions, thereby offering indispensable theoretical support for structural design applications.

Piezoelectric heterogeneous materials are widely used in flexible electronic device design, enhancing sensitivity to external stimuli like pressure and acceleration. Despite their usefulness, analyzing these inherently periodic structures poses significant computational challenges. In response, this paper presents a multiscale isogeometric analysis approach tailored for simulating piezoelectric materials. We introduce an electric–mechanical coupling model using isogeometric analysis (IGA) for two-dimensional piezoelectric membrane structures, assuming the plane stress hypothesis. Our proposed algorithm enables precise calculation of both displacement and electric potential solutions, demonstrating superior convergence properties compared to traditional finite element methods. Furthermore, we extend this approach to multiscale isogeometric analysis for computing numerical solutions in porous structures and heterogeneous composite piezoelectric materials under tensile and bending conditions. Through rigorous numerical testing, we evaluate the proposed extended multiscale isogeometric analysis method, showcasing its efficacy in achieving a balance between computational efficiency and simulation accuracy. This IGA-based electro-mechanical coupling model and numerical algorithm pave the way for more streamlined and precise simulations of piezoelectric materials within the context of flexible electronic devices.

The linear forced vibration characteristics of viscoelastic variable stiffness laminated composite plates (VVSLC) are studied using a generalized Maxwell model and finite element method. The integral form of the viscoelastic constitutive relation is converted to the incremental form for finite element formulation based on the Reissner–Mindlin plate theory. The recursive relations are developed to compute the current time-step solution using only the previous time-step solution. The periodic response directly in the time domain is obtained using shooting technique coupled with Newmark’s time integration method. The implementation of shooting technique for Boltzmann integral-based viscoelasticity for curvilinear fibre composite plates is done for the first time in this study. For the comparison purpose, the response/resonance frequency/modal loss factor is also obtained using equivalent complex modulus based viscoelastic correspondence principle. It is observed that the variation in fibre orientation and boundary conditions leads to significant variations in response, stress/moment resultant amplitude and the damping factor of the VVSLC plates. Further, the present time domain based approach is capable of predicting damping factor at all forcing frequencies whereas complex eigenvalue analysis can predict damping factor only at discrete resonance frequency. Based on the detailed studies, it is found that the curvilinear fibre composite plates depict a significant reduction in response/moment resultants compared to straight fibre composite plates.