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Molecular dynamics (MD) simulations are carried out to study the thermal and mechanical behaviors of single-crystalline wurtzite (WZ), zinc-blende (ZB), and polytypic superlattice ZnS nanowires containing alternating WZ and ZB regions with thicknesses between 1.85 nm and 29.62 nm under tensile loading. The wires analyzed have diameters between 1.77 nm and 5.05 nm. The Green-Kubo method is used to calculate the thermal conductivity of the wires at different deformed states. A non-equilibrium MD approach is used to analyze the thermal transport behavior at the interfaces between different structural regions in the superlattice nanowires (SLNWs). The Young's modulus and thermal conductivity of ZB nanowires are approximately 2%-12% and 23%-35% lower than those of WZ nanowires, respectively. The lower initial residual compressive stress due to higher irregularity of surface atoms causes the Young's modulus of ZB nanowires to be lower. The dependence of the thermal conductivity on structure comes from differences in phonon group velocities associated with the different wires. The thermal conductivity of polytypic superlattice nanowires is up to 55% lower than that of single-crystalline nanowires, primarily because of phonon scattering at the interfaces and the resulting lower effective phonon mean free paths for each structural region. As the periodic lengths (1.85-29.62 nm) and specimen lengths (14.81-59.24 nm) of SLNWs decrease, these effects become more pronounced, causing the thermal conductivity to further decrease by up to 30%. [ABSTRACT FROM AUTHOR]

The demand for large-scale design optimization and probability-based analysis is constantly increasing. In design optimization and stochastic analysis, repeated analyses are required, which impede computational efficiency. Several effective reanalysis techniques using the Sherman-Morrison-Woodbury (SMW) formula have been formulated for application to static analysis. However, it is difficult to directly apply the SMW formula for dynamic reanalysis, and, consequently, substructuring techniques are frequently employed for the dynamic reanalysis. The existing dynamic substructuring finite element techniques require recalculations for all the substructures, including changed elements, even when only a single element is changed; thus, the accuracy is reduced owing to the interface assumption. Therefore, to apply the SMW formula to the dynamic reanalysis, an approach is employed in which, using dynamic condensation, the dynamic problem is transformed into a problem where the SMW formula can be employed. Furthermore, to improve the speed of convergence in the condensation method, the proposed method reuses the condensed matrices calculated in the previous analysis. Thus, the proposed method precisely updates and recalculates only the elements of interest, thus increasing the computation efficiency and accuracy. Several numerical examples are presented to verify the efficiency and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

Through the combination of the recursive multiple thermostat (RMT) Nosé–Poincaré and Parrinello–Rahman methods, the recursive multiple thermostat chained fully flexible unit cell (RMT-NσT) molecular dynamics method is proposed for isothermal-isobaric simulation. The RMT method is known to have the advantage of achieving the ergodicity that is required for canonical sampling of the harmonic oscillator. Thus, an explicit time integration algorithm is developed for RMT-NσT. We examine the ergodicity for various parameters of RMT-NσT using bulk and thin film structures with different numbers of copper atoms and thicknesses in various environments. Through the numerical simulations, we conclude that the RMT-NσT method is advantageous in the cases of lower temperatures. [ABSTRACT FROM AUTHOR]

The recursive thermostat chained fully flexible cell molecular dynamic simulation (NσT ensemble) is performed. The ensemble is based on the metric tensor, whose components are used as extended variables. These variables are combined with Nosé-Poincaré recursive thermostat chains. This extended Hamiltonian approach preserves Hamiltonian in structure, and the partition function satisfies the NσT ensemble state in phase space. In the present study, the generalized leap frog method was employed for time integration. The resulting molecular dynamics simulation was performed for bulk and thin film solid materials in the face-centered-cubic crystal structure. Uniaxial tension test and simple shear test are performed to predict the behaviors of a solid material in the bulk state and nanoscale thin film state. The proposed flexible cell method should serve as a powerful tool for the prediction of mechanical and thermal properties of solid materials including nanoscale behavior. [ABSTRACT FROM AUTHOR]

First-principle calculations are carried out to study the diffusion of Li ions in rutile structure RuO2, a material for positive electrodes in rechargeable Li ion batteries. The calculations focus on migration pathways and energy barriers for diffusion in Li-poor and Li-rich phases using the Nudged Elastic Band Method. Diffusion coefficients estimated based on calculated energy barriers are in good agreement with experimental values reported in the literature. The results confirm the anisotropic nature of diffusion of Li ions in one-dimensional c channels along the [001] crystalline direction of rutile RuO2 and show that Li diffusion in the Li-poor phase is faster than in the Li-rich phase. The findings of fast Li diffusion and feasible Li insertion at low temperatures in the host rutile RuO2 suggest this material is a good ionic conductor for Li transport. The finding also suggests possible means for enhancing the performance of RuO2 -based electrode materials. [ABSTRACT FROM AUTHOR]

The article presents a study which proposed the inverse perturbation method (IPM) and an iterated improved reduced system (IIRS) technique for accelerating solution convergence. It explains the governing equation for undamped free vibration in the finite element analysis. The efficiency of the IIPM through numerical examples of damage detection is examined. It was concluded that errors in the transformation matrix can be minimized through using the reduced system method and the computational times and consumption of computer memory are also reduced.

A new first-order shear deformation theory (FSDT) has been developed and verified for laminated plates and sandwich plates. Based on the definition of Reissener-Mindlin's plate theory, the average transverse shear strains, which are constant through the thickness, are improved to vary through the thickness. It is assumed that the displacement and in-plane strain fields of FSDT can approximate, in an average sense, those of three-dimensional theory. Relationship between FSDT and three-dimensional theory has been systematically established in the averaged least-square sense. This relationship provides the closed-form recovering relations for three-dimensional variables expressed in terms of FSDT variables as well as the improved transverse shear strains. This paper makes two main contributions. First an enhanced first-order shear deformation theory (EFSDT) has been developed using an available higher-order plate theory. Second, it is shown that the displacement fields of any higher-order plate theories can be recovered by EFSDT variables. The present approach is applied to an efficient higher-order plate theory. Comparisons of deflection and stresses of the laminated plates and sandwich plates using present theory are made with the original FSDT and three-dimensional exact solutions. [ABSTRACT FROM AUTHOR]

Dynamic analysis of structural systems requires a considerable amount of computing time. Because the dynamic behavior of a structure is dominated by lower modes, all of the eigenvalues of the system need not be calculated. The previously proposed methods approximate the eigenvalues of a global system but they take great amount of computing time to construct a reduced system. An element-level energy estimation technique is proposed to construct a reduced finite element model. Through several examples, it is demonstrated that the proposed method effectively saves computational time and accurately predicts the eigenvalues of a global system. [ABSTRACT FROM AUTHOR]

The layup optimization of the maximum strength of laminated composites with free edge by genetic algorithm (GA) is presented. To efficiently calculate the interlaminar stresses of composite laminates with free edges, the extended Kantorovich method was applied. In the formulation of GA, a repair strategy was adopted to satisfy given constraints. Multiple elitism schemes were implemented to efficiently find multiple global optima or near optima. A convex modeling technique is proposed to consider the bounded uncertainty of material properties. Results of the GA optimization with scattered properties were compared with those of optimization with nominal properties. The GA combined with convex modeling can work as a practical tool for lightweight design of laminated composite structures because geometric and material uncertainties are always encountered in composite materials. [ABSTRACT FROM AUTHOR]

A higher-order zigzag theory has been developed for laminated composite shells with multiple delaminations. General tensor-based formulation is developed for arbitrary curved shell with exact geometric description. A laminated shell theory with multiple delaminations for generallamination configurations is obtained by superposing a cubic varying displacement on a zigzag linearly varying displacement. The von Káirmán nonlinearity is included in the formulation for the potentialities of addressing problems requiring geometric nonlinearity such as large deflection and postbuckling problems. When top and bottom surface transverse shear stress free conditions and interface transverse shear continuity conditions including delamination interfaces are imposed the displacement of the minimal degrees of freedom is obtained. The proposed displacement field can systematically handle the number, shape, size, and locations of the delaminations. Through the variational principle, equilibrium equations and variationally consistent boundary conditions are obtained. To assess the accuracy and efficiency of the present theory, the linear buckling problem of cylindrical shell with multiple delaminations has been analyzed. The higherorder zigzag theory should work as an efficient tool for analyzing the behavior of composite laminated shells with multiple delaminations. [ABSTRACT FROM AUTHOR]

Discusses the stability of delaminated composites using layerwise finite elements. Global-local approach for bifurcation problems with multiple delaminations; Utilization of a displacement field matching method; Determination of the number of degrees of freedom (DOF) of undelaminated zone; Reduction of global DOF's.

Describes the development of an improved Mindlin plate stress analysis for laminated composites in finite element method. Determination of] in-plane and transverse stresses; Advantages of efficient high-order plate theory; Application of first-order shear deformation plate theory.

Due to the enhanced interaction among constituents and the resultant effect of particle size on the elastic modulus, nanocomposites with volume fractions higher than 12% show critical nondilute concentrations. In order to describe nondilute concentrations and the effect of particle size, a multi-inclusion model was adopted and a method was developed to transfer nanoscale physical information to a continuum-based analytical model. The accuracy and applicability of the present scale-bridging method at dilute and nondilute concentrations were verified by comparing results of the present method with those of molecular dynamics and finite element analysis. [ABSTRACT FROM AUTHOR]

Multiscale analysis to characterize the size effect of silica nanoparticles on the mechanical properties of nanoparticle/polymer nanocomposites is developed and verified through a molecular dynamics simulation and continuum micromechanics model. In the micromechanics model, the particle-matrix interface mechanical property is incorporated, and the thickness and elastic properties of the interface are extracted from the atomistic structures. The proposed multiscale micromechanics model accurately reflects the size effect of the nanoparticle. The prediction by the current multiscale model at various volume fractions is compared to the results of the molecular dynamics simulations in order to validate the present multiscale analysis model. [ABSTRACT FROM AUTHOR]

Model updating processes are important for improving a model's accuracy by considering experimental data. Structural system identification was achieved here by applying the degree-of-freedom-based reduction method and the inverse perturbation method. Experimental data were obtained using the specific sensor location selection method. Experimental vibration data were restored to a full finite element model using the reduction method to compare and update the numerical model. Applied iteratively, the improved reduced system method boosts model accuracy during full model restoration; however, iterative processes are time consuming. The computation efficiency was improved using the system equivalent reduction-expansion process in concert with proper orthogonal decomposition. A convolutional neural network was trained and applied to the updating process. We propose the use of an efficient model updating method using a convolutional neural network to reduce computation time. Experimental and numerical examples were adopted to examine the efficiency and accuracy of the model updating method using a convolutional neural network. [ABSTRACT FROM AUTHOR]

The development of breast implant technology continues to evolve over time, but changes in breast shape after implantation have not been fully elucidated. Thus, we performed computerized finite element analysis in order to better understand the trajectory of changes and stress variation after breast implantation. The finite element analysis of changes in breast shape involved two components: a static analysis of the position where the implant is inserted, and a dynamic analysis of the downward pressure applied in the direction of gravity during physical activity. Through this finite element analysis, in terms of extrinsic changes, it was found that the dimensions of the breast implant and the position of the top-point did not directly correspond to the trajectory of changes in the breast after implantation. In addition, in terms of internal changes, static and dynamic analysis showed that implants with a lower top-point led to an increased amount of stress applied to the lower thorax. The maximum stress values were 1.6 to 2 times larger in the dynamic analysis than in the static analysis. This finding has important implications for plastic surgeons who are concerned with long-term changes or side effects, such as bottoming-out, after anatomic implant placement. [ABSTRACT FROM AUTHOR]

The structural-vibration behavior of a plate model is expressed as a combination of the initial state behavior of the structure and its associated perturbations. The dynamic behavior obtained from a limited number of accessible nodes and their associated degrees of freedom is employed to detect structural changes that are consistent with the perturbations. The equilibrium model is described in terms of the measured and unmeasured modal data. Unmeasured information is estimated using an iterated improved reduction scheme. Because the identification problem depends on the measured information, the quality of the measured data determines the accuracy of the identified model and the convergence of the identification problem. The accuracy of the identification depends on the measurement/sensor location. In this study, a more accurate identification method using the optimal sensor-location selection method is proposed. Experimental examples are employed to examine the convergence and accuracy of the proposed method applied to an inverse problem of system identification. [ABSTRACT FROM AUTHOR]

The thermoelastic properties of SiC/epoxy nanocomposites are investigated through a molecular dynamics (MDs) simulation and micromechanics bridging method. One major finding from the MD simulation is that not only the elastic modulus but also the thermal expansion coefficient of the nanocomposites exhibits particle-size dependency at fixed volume fractions. In order to describe such effects that are observed from atomistic simulations, a micromechanics-based scale bridging method is suggested that handles both the elastic and residual fields of the nanocomposites with the help of the effective interface concept and sequential information transfer. [ABSTRACT FROM AUTHOR]

By the chemical cross-linking of rigid molecules, liquid crystal polymer (LCP) has been envisaged as a novel heterogeneous material due to the fact that various optical and geometric states of the liquid crystalline (LC) phases are projected onto the polymeric constituents. The phase behavior, which refers to the macroscopic shape change of LCP under thermotropic phase change, is a compelling example of such optical-mechanical coupling. In this study, the photomechanical behavior, which broadly refers to the thermal- or light-induced actuation of smectic solids, is investigated using three-dimensional nonlinear finite element analysis (FEA). First, the various phases of LC are considered as well as their relation to polymeric conformation defined by the strain energy of the smectic polymer; a comprehensive constitutive equation that bridges the strong, optomechanical coupling is then derived. Such photomechanical coupling is incorporated in the FEA considering geometric nonlinearity, which is vital to understanding the large-scale light-induced bending behavior of the smectic solid. To demonstrate the simulation capability of the present model, numerous examples of photomechanical deformations are investigated parametrically, either by changing the operating conditions such as stimuli (postsynthesis) or the intrinsic properties (presynthesis). When compared to nematic solids, distinguished behaviors due to smectic substances are found herein and discussed through experiments. The quasisoftness that bidirectionally couples microscopic variables to mechanical behavior is also explained, while considering the effect of nonlinearity. In addition to providing a comprehensive measure that could deepen the knowledge of photomechanical coupling, the use of the proposed finite element framework offers an insight into the design of light-responsive actuating systems made of smectic solids. [ABSTRACT FROM AUTHOR]

We report the introduction of p-type conductivity in high-Mn, Li-rich oxides (HMLOs) by the introduction of Cu doping to improve intrinsic electronic conduction. The study is based on experimental observations and a fundamental understanding through first-principles electronic structure analysis. Although the Cu-doped HMLO (CuHMLO) has a crystal structure identical to the original HMLO, the electrochemical performance of CuHMLO is superior in terms of specific energy and power characteristics. Specifically, CuHMLO exhibits a larger specific capacity with enhanced rate capability, and could be charged at lower voltages and discharged at higher voltages. For the first-principles calculations, HMLO and CuHMLO structures are modeled based on Rietveld refinement of the powder X-ray diffraction data of the powders synthesized herein. The electronic structure of CuHMLO reveals the generation of an electron hole in the valence band, above the Fermi level, indicating p-type conductivity and improving the electronic conductivity. The interpretation based on the crystal field theory elucidates that the generation of this electron hole is responsible for the relatively reduced character of Cu than Mn in the highly oxidized HMLO environment. Combination of this observed enhancement with a fundamental understanding on the origin of the p-type conductivity could assist in improving the specific energy and power characteristics of Li-rich oxides. [ABSTRACT FROM AUTHOR]

The photomechanical behavior of azobenzene-functionalized liquid-crystalline polymers (azo-LCPs) is closely related to UV light propagation. Here, we report the effect of light absorption by the LC host and the concerted isomerism of azobenzene on this property. In situ measurements of light absorptivity and computer simulations revealed that the light propagation of a liquid-crystalline polymer is affected by the UV absorption of the LC host under the same concerted isomerism of azobenzene. The lower UV light absorption of the LC host results in deeper UV light propagation and a sharper isomerization profile, which eventually induces faster bending when compared to the higher UV light absorption of the LC host. On the other hand, increasing the azobenzene concentration in the polymer greatly decreases the speed of light propagation, which is regarded as one of the factors inhibiting further increases in the bending speed of azo-LCP films. [ABSTRACT FROM AUTHOR]

This work finds that LiVO3 is lithiated by a conversion reaction at 25 °C, which is unusual for the family of vanadium oxides. The spectroscopic studies and first-principle calculations performed on the lithiation mechanism of LiVO3 consistently propose that a two-phase insertion-type lithiation proceeds in the early stage of lithiation; LiVO3 transforms into a rock-salt structured Li2VO3. The continuing single-phase Li+ insertion into the tetrahedral sites in the rock-salt Li2VO3 produces a more Li-rich phase (Li2.5VO3), which is highly distorted because of the unfavorable Li+ insertion into the tetrahedral sites such as to be vulnerable to lattice breakdown. Hence, a two-phase (nucleation/growth type) conversion reaction is followed along with a structural disintegration; the Li2.5VO3 phase decomposes into metallic vanadium and Li2O. To determine the factors facilitating the conversion reaction of LiVO3, galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) are performed on LiVO3, the results of which are then compared to those observed with V2O5, which is not lithiated by the conversion reaction at 25 °C. The results show that the quasi-equilibrium potential for the conversion reaction is more positive for LiVO3 (thermodynamically more feasible). Also, the conversion reaction is kinetically more facilitated for LiVO3 due to faster solid-state diffusion of mobile ionic species during the two-phase growth stage of metallic vanadium and lithium oxide (Li2O) in the conversion process. [ABSTRACT FROM AUTHOR]

An enhanced first-order shear deformation theory (EFSDT) is developed for linear viscoelastic analysis of laminated composite and sandwich plates. Improved strain energy expression of the conventional Reissner/Mindlin first-order shear deformation theory (FSDT) through strain energy transformation is derived in the Laplace domain by minimizing the strain energy difference between FSDT and an efficient higher-order zigzag theory (EHOPT). The convolution theorem of Laplace transformation is applied to circumvent the complexity of dealing with linear viscoelastic materials. The present EFSDT with the Laplace domain approach has the same computational advantage of the conventional FSDT while improving upon the accuracy of the viscoelastic response by utilizing the postprocess recovery procedure. The accuracy and efficiency of the proposed theory are demonstrated through the numerical results obtained herein by comparing to those available in the open literature. [ABSTRACT FROM AUTHOR]

As a polymeric system incorporating rigid molecules within its structure, the liquid-crystal network (LCN) has been envisaged as a novel heterogeneous material. Under the influence of external stimuli, the orientational order of the liquid-crystalline phase becomes dilute and overall anisotropy is hence decreased; the actinic light absorbed by photochromic molecules, for example, induces the geometric isomerization and subsequently yields internal stress within the local network. In this study we investigate light- and temperature-induced spontaneous deformations of the LCN structure via a three-dimensional finite element model that incorporates geometric nonlinearity with a photomechanical constitutive model. We first examine the bending behavior and its nonlinearity and then parametrically study the various behaviors that stem from different origins ranging from the microscale to the macroscale: (i) the geometry of the LCN film, (ii) the macroscopic global order, (iii) the distorted mesogenic orientation due to the Fredericks distortion, and (iv) defect-induced instability. These interrelated behaviors demonstrate both the simulation capability and the necessity of the presenting framework. By employing a nonlinear consideration along with a microscopic shape parameter r the present approach facilitates further understanding of photomechanical physics such as the deconvolution of various stimuli and the deformed shape obtained due to snap-through instability. Furthermore, this study may offer insight into the design of light-sensitive actuation systems by deepening our knowledge and providing an efficient measure. [ABSTRACT FROM AUTHOR]

The opto-mechanical properties of a photo-responsive nematic polymer network (PRPN) are investigated using molecular dynamics simulation. For the implementation of the trans-to-cis isomerization of azo compounds, a switchable potential formalism for the N = N bond is applied to the crosslinked PRPN unit cell model. During the light switch-on and heating-up simulations at a wide range of temperatures, the scalar orientational order parameter for the mesogenic side group molecules, the effective photo-induced strain of the bulk polymer network, and the opto-mechanical properties are characterized. The correlation between the microstate which belongs to the molecular location and the macroscopically observed photostrain is identified according to the isomerization ratio of the diazene groups. [ABSTRACT FROM AUTHOR]

Clamping loss caused by elastic wave radiation to a support is one of the most dominant loss mechanisms in predicting the quality factor of very or ultra high frequency nanocantilever resonators. To consider nanosurface effects and different scales of the resonator and support, we propose a multiscale model combining a scale-bridging model for the resonator and a perfectly matched layer to estimate the loss in the support. The proposed model is used to investigate the surface effect on the nanoresonator and also shows the tradeoff between the resonant frequency and the quality factor with or without the surface effects. [ABSTRACT FROM AUTHOR]