International Journal of Mechanics and Materials in Design最新文献

The literature contains numerous articles devoted to examining the mechanical behavior of nanowires (NWs) using molecular dynamics simulations. Many of these investigations have selected improper strain rates leading to erroneous results concerning ductile–brittle transition. In this study, we tested this hypothesis and proved that such transition in the material behavior existed due to the improper selection of strain rates which eventually changes the propagation velocity of phonons in the conducted atomistic simulations. In the current study, we subjected gold nanowires (Au NWs) with a diameter of 100 Å and lengths ranging from 25 to 1000 Å to varied strain rates. Specifically, we examined the effect of the rate of deformation of the NW upon its mechanical behaviour by dividing its length into several stations along its entire length to capture the strain distribution in each segment along that length. Five orders of magnitudes of strain rates were applied in our work for studying the influence of rate of deformation on the strain distribution along the NW length. The results of our molecular dynamics simulations show that smaller strain rates were necessary for modeling relatively long (> 150 Å) NWs to ensure the transmission of the applied loads through the entire NW length to suppress phonon drag effect. On the other hand, relatively short (< 25 Å) NWs experience large variations in the axial strain along the NW length; with smaller strains near the ends and higher strains at the middle section. As a result, relatively short NWs exhibit higher elastic moduli than longer ones and the NW length’s effect diminishes at lengths exceeding 150 Å. Location of necking, under the application of higher strain rate, shifts away from the loading end of NW towards its middle portion with the decrease in the NW length due to the phonon drag. The slope of the stress–strain curves was found to significantly depend on the NW length, and thus, using the same strain rate over a large range of NW lengths will lead to erroneous results.

Materials are of prime importance for designing and manufacturing structures and components in numerous industries, including aviation, aerospace, military, automotive, machine construction, electronics, and telecommunications, among others. Throughout the industrial transformations in human history, it is evident that the materials industry had the most significant impact on scientific and technological progress. In recent years, the Fourth Industrial Revolution has altered the infrastructure and character of production in a number of global industries. Materials science has been contributing a significant and essential role in the global competitiveness of all industries, particularly those utilizing electronic domains such as semiconductors, microprocessors, and sensors for industrial and social applications. Consequently, nanoscale materials with exceptional properties have garnered the interest of numerous researchers. One of these phenomena in dielectric materials is flexoelectricity. This phenomenon was discovered in the 1950s of the previous century, but it wasn't until the early 2000s, when materials science and other disciplines flourished, that many researchers began to focus on it. In recent years, the applicability of flexoelectric materials has increased across all disciplines. In addition, as a consequence of the importance of novel electrical materials to the flexoelectric effect, the research problem for this material broadly and the analysis of the mechanical responses of flexoelectric structures are being investigated and developed at a rapid rate. This paper provides an overview of the flexoelectric phenomenon, together with potential applications and recommendations for further study. The article’s content will serve as a valuable resource for scientists interested in dielectric materials with unique electromechanical effects, which are extensively used in contemporary electronic disciplines.

Based on the theory of flexoelectricity in elastic dielectrics and the principle of minimum potential energy, a new theoretical model of bilayer circular nano-plate containing a piezoelectric layer is constructed. This model is used to analyze the effects of external loading, applied voltage, flexoelectric effect, and surface effect on the bending deflection, polarization, and normalized electric potential of the nano-plate. Numerical results indicate that external loading and applied voltage have opposite effects on the radial deflection of the bilayer circular nano-plate, with external loading having a more significant influence on deflection than the flexoelectric effect. Applied voltage also affects the normalized electric potential of the bilayer nano-plate. In the presence of negative surface residual stress, the deflection is mainly influenced by the flexoelectric effect. When the surface residual stress is positive and the ratio of radius to thickness is less than 25, the surface effect dominates the deflection behavior. Additionally, the positive or negative surface residual stress leads to an increase or decrease in polarization. The results provide a theoretical basis for the design of intelligent components containing piezoelectric bilayer circular nano-plates.

This article aims to develop a novel approach to non-probabilistic reliability-based multi-material topology optimization with stress constraints to address the optimization design problem considering external loading uncertainties. To be specific, the ordered solid isotropic material with penalization multi-material interpolation model is introduced into the non-probabilistic reliability-based topology optimization considering structural volume minimization under stress constraints, the multidimensional ellipsoidal model describes the non-probabilistic uncertainty. By utilizing the first-order reliability method, the failure probability can be estimated, and a non-probabilistic reliability index can be obtained. The global maximum stress is measured by adopting the normalized p-norm function method in combination with relaxation stress. The sensitivity analysis of the stress constraints is derived by the adjoint variable method, and the method of moving asymptote is employed to solve the design variables. Through several numerical examples, the effectiveness and feasibility of the presented method are verified to consider multi-material topology optimization with stress constraints in the absence of accurate probability distribution information of uncertain variables.

This study focuses on using various machine learning (ML) models to evaluate the shear behaviors of ultra-high-performance concrete (UHPC) beams reinforced with glass fiber-reinforced polymer (GFRP) bars. The main objective of the study is to predict the shear strength of UHPC beams reinforced with GFRP bars using ML models. We use four different ML models: support vector machine (SVM), artificial neural network (ANN), random forest (R.F.), and extreme gradient boosting (XGBoost). The experimental database used in the study is acquired from various literature sources and comprises 54 test observations with 11 input features. These input features are likely parameters related to the composition, geometry, and properties of the UHPC beams and GFRP bars. To ensure the ML models' generalizability and scalability, random search methods are utilized to tune the hyperparameters of the algorithms. This tuning process helps improve the performance of the models when predicting the shear strength. The study uses the ACI318M-14 and Eurocode 2 standard building codes to predict the shear capacity behavior of GFRP bars-reinforced UHPC I-shaped beams. The ML models' predictions are compared to the results obtained from these building code standards. According to the findings, the XGBoost model demonstrates the highest predictive test performance among the investigated ML models. The study employs the SHAP (SHapley Additive exPlanations) analysis to assess the significance of each input parameter in the ML models' predictive capabilities. A Taylor diagram is used to statistically compare the accuracy of the ML models. This study concludes that ML models, particularly XGBoost, can effectively predict the shear capacity behavior of GFRP bars-reinforced UHPC I-shaped beams.

An effective human–machine interface is of utmost importance. However, the current methods for designing contact contours are not entirely flawless, frequently relying on experience and multiple design iterations, and are challenging to achieve the desired distribution of target contact pressure. This study proposes a novel design method for contact contour that is based on the equilibrium relationship under contact conditions and is aimed at achieving target contact pressure. The mechanical properties of human tissue were analyzed, and a finite element model of the human body was established. Using two design cases of a wheelchair cushion and a bicycle saddle, contact pressure distribution was constructed based on design expectations. The deformed surface profile of the human body under the target contact pressure distribution was obtained through simulation. Additionally, the mechanical properties of polyurethane hyper-elastic foam and its variation with model parameters were analyzed, and a mathematical model of it was established. The deformation of foam was calculated and compensated to the deformed body surface according to the target pressure, and the reconstructed contour was then obtained and fitted to the design contour. A control group model was constructed, and contact simulation was used to validate the designed contour. The simulation results of both design cases showed that the difference between the contact pressure distribution of the design contour and the target contact pressure distribution was small, and it was better than the traditional empirical design contour of the control group, thus verifying the feasibility of this method.

Low impact docking mechanism (LIDM) is a key fundamental equipment for space missions that is used to capture and connect vehicles. Its strict requirements for mass and volume makes a major challenge to achieve larger workspace and load capacity (the docking direction is maximum). Essentially, it is a Gough–Stewart platform (SP), and the main design difficulties are configuration design and dimension optimization. The paper proposed a new integrated joint and SP classification, which guide the configuration design. Meanwhile, a unified kinematics model is established by the vector method, and the force Jacobian matrix is obtained by the principle of virtual work. The key to dimension optimization is to seek a reasonable evaluation index. A proposed general evaluation index, task-oriented force ellipsoid (TOFE), is applicable to both isotropic and anisotropic design demands. It normalizes the input and output, transforms an anisotropic problem into an isotropic problem, and uses the smallest hypersphere radius as the characterization. Then, using non-dominated sorting genetic algorithm (NSGA-II) obtain the Pareto front of the workspace and load capacity. Moreover, the influence of dimension parameters on output performance was revealed. Finally, the dimension optimization of the LIDM is completed, and its load capacity is improved by 13.51%.

This paper presents an analytical model to investigate the static behaviour of sandwich plates comprised of two isotropic face sheets and a honeycomb core. Through-thickness transverse shear stresses were considered using a unified displacement field with which various plate theories were implemented, i.e., exponential, third-order, hyperbolic, sinusoidal, fifth-order, Mindlin, and the classic plate theory. The equilibrium equations of a simply-supported sandwich panel were derived using the principle of virtual work and Navier solution was obtained under static transverse loading. After validating of the model, various mechanical and geometrical parameters were varied to characterise the behaviour of the structure under regular and auxetic response. It was found that the auxeticity of the core strongly affects the mechanical response, e.g., in controlling deflection, in-plane anisotropy, and Poisson’s ratio. Cell wall angle was found to be most critical parameter that can be used to adjust anisotropy, out-of-plane shear modulus, transverse shear stress distribution, and deflection of the panel. Also the cell aspect ratio controls the sensitivity of the core response to other geometrical variations. In terms of the higher-order theories, the deflection-dependent parameter of the unified formulation seems to have more control of maximum deflection compared to independent rotations. Auxeticity of the core showed some benefits in controlling anisotropy, deflection and providing additional out-of-plane shear rigidity. Overall, since there is not one-to-one relationship between specific values of Poisson’s ratio, anisotropy, and shear rigidity, careful design considerations must be invested to obtain a correct mechanical response.

We study the three-dimensional problem associated with an incompressible nonlinear elastic spherical inhomogeneity embedded in an infinite linear isotropic elastic matrix subjected to a uniform deviatoric load at infinity. The nonlinear elastic material can incorporate both power-law hardening and softening materials. The inhomogeneity-matrix interface is a spring-type imperfect interface characterized by a common interface parameter for both the normal and tangential directions. It is proved that the internal stresses and strains within the spherical inhomogeneity are unconditionally uniform. The original boundary value problem is reduced to a single non-linear equation which is proved rigorously to have a unique solution which can be found numerically. Furthermore, the neutrality of the imperfectly bonded nonlinear elastic spherical inhomogeneity is accomplished in an analytical manner. Finally, we prove the uniformity of the internal elastic field of stresses and strains inside an incompressible power-law hardening or softening nonlinear elastic ellipsoidal inhomogeneity perfectly bonded to an infinite linear isotropic elastic matrix subjected to uniform remote shear stresses and strains.

This research proposes a Chebyshev–Ritz solution for analysing the size-dependent behaviour of porous microbeams. The displacement field is based on the higher-order beam theory, while the size-dependent effect is accounted for using the modified couple stress theory. Moreover, porous microbeams’ elasticity moduli and mass density are assumed to be graded in the thickness direction according to four distinct distribution patterns. The open-cell metal foam exemplifies a characteristic mechanical attribute that facilitates the determination of the interrelation between coefficients of density and porosity. To derive the governing equations, the Lagrange’s principle is employed. Four types of boundary conditions, including clamped–clamped, clamped-simply supported, clamped-free, and simply-supported, along with four porosity distribution types of the beam, are considered. The Chebyshev polynomial is developed to analyse the porous microbeams’ buckling, free vibration, and bending. Furthermore, the study discusses the impacts of the material length scale parameter, porosity, slenderness, boundary condition, and porosity type on their mechanical responses. Finally, some novel results are presented, which can serve as benchmarks for future studies.