International Journal of Mechanics and Materials in Design最新文献

In this work, the phase-field framework coupled with J2 plasticity is expressed in the variational formulation to simulate the bimaterial interfacial problems. The quadratic energetic degradation function in conjunction with the AT2 model is employed for phase-field regularization. A load increment-independent and computationally efficient Staggered scheme is proposed to solve the phase field problems. The existing unconditionally stable quasi-Newton-based Monolithic scheme, which captures the cracking in brittle solids has been extended to capture the crack evolution in the elastoplastic solids using the return mapping algorithm. A Generalized user-defined element subroutine (UEL) is developed and implemented in the commercial software ABAQUS using the proposed Staggered and Monolithic schemes. The efficacy of the proposed algorithms was validated against existing literature and extended to study bimaterials with interfaces. Different geometry and loading configurations in the bimaterial and their interface are modeled using the phase-field framework and analyzed using proposed schemes. The contour plots of phase field for crack evolution, equivalent plastic strain, and reaction force are presented. The efficacy of proposed algorithms in terms of the total number of iterations and the computational CPU time is provided for all numerically simulated cases.

The Industry 4.0 has focus on connected devices and machines. It needs a number of sensors connected with each other and transfer of the information. Most of the sensors and sensor nodes require low power. In remote areas, where the power is limited, self-powered devices are more useful. Wind is available everywhere but the wind speed varies from place to place. Windmills are being used to generate electric power from the wind, however, is restricted due to large size and high cost. In this paper, it is proposed to develop a magnetic excited rotary harvester to harvest power at low wind speed. This can solve one of the major problems of frequent replacement of the battery in remote devices required for sensor and sensor nodes. To convert the rotation of the windmill to electric power, the rotation energy is converted to vibrating motion of a piezoelectric cantilever beam. The vibrations in the beam are generated with the help of interaction of magnetic field on the stator and blade mounted on the rotating shaft. The vibrations are then converted to electric charge due to the property of the piezoelectric material. An analytical model is developed and the results are compared with experiments. It is observed that at minimum wind speed of 2 m/s the estimated power is 1.06 mW while at a normal wind speed of 5 m/s power is calculated as 2.21 mW from the device.

A finite element method using a 9-node isoparametric plate bending element, incorporating the effects of transverse shear based on the first-order shear deformation theory, is proposed for the free vibration analysis of rectangular cut-out plates resting on an elastic foundation. The elastic foundation is modeled on the Winkler and the Pasternak type, and equations of motion are obtained using the principle of virtual work. To account for the parabolic strain variation through the thickness, a shear correction factor of 5/6 is used, and the effect of rotary inertia has been included in the formulation. The present formulation is compared with established results obtained using analytical methods, with and without rotary inertia, and the max variation observed is 2.24% without rotary inertia and 0.02% with rotary inertia. Cut-out plates are validated with results obtained using the finite element method, and the max variation observed between established results and present formulation is 1.3%. Establishing the accuracy of the current formulation, new results are obtained for rectangular cut-out plates resting on an elastic foundation of various stiffness parameters. The effect of incrementing cut-out dimensions and different layouts of cut-outs in the plate on the free vibration response of plates resting on an elastic foundation is investigated, along with the effects of varying aspect ratios and thickness-to-side ratios.

Thin film structures will be wrinkled due to buckling deformation under the influence of compressive stress. The wrinkle and tension states of the thin film can be changed by introducing microstructures. So we introduce rigid elements on the thin film to suppress the wrinkling behavior of the thin film, and propose a method to calculate the optimal distribution position of the rigid elements on the thin film. Using this method, the optimal distribution positions of the square rigid elements on the biaxially stretched square thin film were calculated, and the effectiveness of introducing rigid elements on the thin film to suppress the wrinkle was verified through numerical simulation and experimental research. The results show that the wrinkling behaviour of the film can be effectively suppressed by placing rigid elements at the optimal position obtained by the method proposed to this paper. Our findings could provide new design ideas for thin-film antenna structures in aerospace engineering.

This paper presents a size-dependent isogeometric analysis of smart functionally graded porous nanoscale plates made of two piezoelectric materials. Two porous distributions, namely even and uneven, are considered along the thickness direction. To take into account for size-dependent effects, the nonlocal elasticity theory proposed by Eringen is employed to investigate the behaviors of the smart nanoplate. An electric potential field is adopted based on the Maxwell's equation. The governing equations for smart functionally graded piezoelectric porous nanoplates are obtained and utilized by a combination of higher-order shear deformation theory and non-uniform rational B-splines formulations. The present approximation is capable of meeting the necessary conditions with at least third-order derivatives in the approximate formulations of the smart nanoplate. The natural frequencies of the smart nanoplate are fully investigated by studying the influences of power-law index, external electric voltage, porosity coefficient, boundary condition, porosity distributions, and nonlocal parameter, respectively. The present results, when compared to those from published documents, have been evaluated and found to be both reliable and effective. This paper reports several new computational results that can be of great interest to researchers due to the innovative approach and both the development and future application for smart nanostructures.

In this paper a structural optimization framework is developed to design three-dimensional periodic lattice unit cells that meets specific mechanical requirements. The work is motivated by the high design freedom of additive manufacturing technologies, which enable complex multiscale lattice structures to be printed. An optimized lattice unit cell delivers desired orthotropic elastic material properties, providing a tailored metamaterial. The design variables are the coordinates of lattice skeleton nodes defined within the three-dimensional lattice cell space, and the connectivities between them resulting a strut-skeleton. Genetic algorithm (GA) is combined with posterior particle swarm optimization (PSO) algorithm to establish an integrated topology and shape optimization tool. For the calculation of the elastic properties of the individual lattice cells, an effective Timoshenko beam-based finite element calculation method was developed. The novelty of the work stems from its free topology optimization nature, excluding the strut diameters from the optimization variables. The method is demonstrated by four lattice cell optimization cases, where extreme orthotropic elastic properties were targeted and achieved. The tailored lattice cells represent a metamaterial, that can be used to build a structural component on the macroscopic scale, by stacking the cells periodically together, to fill the macroscopic 3D design space. This framework is a strong basis that can be extended to meet further nonlinear metamaterial requirements, such as energy absorption.

In this paper, a multiscale optimization approach for composite material design is presented. The objective is to find different material designs for a short fiber reinforced polymer (SFRP) with a desired effective (in general anisotropic) viscoelastic behavior. The paper extends the work of Staub et al. (2012) and proposes a combination of material homogenization, surrogate modeling, parameter optimization and robustness analysis. A variety of microstructure design parameters including the fiber volume fraction, the fiber orientation distribution, the linear elastic fiber properties, and the temperature dependent material behavior are considered. For the solution of the structural optimization problem, a surrogate-based optimization framework is developed. The individual steps of that framework consist of using design of experiments (DoE) for the sampling of the constraint material design space, numerical homogenization for the creation of a material property database, a surrogate modeling approach for the interpolation of the single effective viscoelastic parameters and the use of differential evolution (DE) for optimization. In the numerical homogenization step, creep simulations on virtually created representative volume elements (RVEs) are performed and a fast Fourier transform (FFT)-based homogenization is used to obtain the effective viscoelastic material parameters. For every identified optimal design, the robustness is evaluated. The considered Kriging surrogate models of Kriging type have a high prediction accuracy. Numerical examples demonstrate the efficiency of the proposed approach in determining SFRPs with target viscoelastic behavior. An experimental validation shows a good agreement of the homogenization method with corresponding measurements. During the manufacturing of composite parts, the results of such optimizations allow a consideration of the local microstructure in order to achieve the desired macroscopic viscoelastic behavior.

The effects of structural nonlinearity (including rubber material and contact boundary nonlinearities) and variable wheel/rail contact point on the dynamic characteristics of resilient wheels are studied to investigate the mechanical properties of these wheels. Primarily, static and dynamic tests are designed to determine the nonlinear constitutive relationship of rubber materials in resilient wheels, and the viscoelastic properties of rubber are discussed. On this basis, the mapping relationship between the elastic modulus and stiffness of rubber in a resilient wheel system is deduced, and the stiffness characteristics of viscoelastic rubber materials are determined. The dynamic models of four types of wheels namely, a solid wheel (SW), a resilient wheel that considers linear rubber (RWL), a resilient wheel that considers nonlinear rubber (RWNL), and a resilient wheel that considers nonlinear rubber and contact boundary (RWNC), are established on the basis of the Yeoh constitutive model for hyper-elastic materials. The changes in wheel/rail contact point and wheel/rail force during train running are obtained under long/short wave irregularity excitation by adopting an established vehicle–track coupled dynamic model. Then the nonlinear dynamic behavior of resilient wheels subjected to varying wheel/rail contact point and wheel/rail force is studied. Finally, the influences of rubber material parameters on the dynamic characteristics of resilient wheels are explored. Results show that the acceleration of a resilient wheel is effectively reduced compared with that of SW. Resilient wheel acceleration that considers variable wheel/rail contact point is larger than that without considering the change in wheel/rail contact point. The deformation rates of rubber subjected to variable and constant wheel/rail contact behavior are 7 and 10%, respectively, and the midpoint deformation of rubber is less than its endpoint deformation. Compared with that of SW, the acceleration of RWL is reduced by 10 and 17% respectively under variable and constant wheel/rail contact points, respectively. Meanwhile, the acceleration of RWNL is reduced by 9 and 7% compared with that of RWL. The influences of nonlinear material characteristics and contact boundary on the dynamic characteristics of resilient wheels are not evident. The major vibration frequencies of the four types of wheels are 3–5, 10, and 22 Hz. The vibration and deformation of resilient wheels increase with an increase in the hardness of rubber.

Energy harvesting from multiple modes using piezoelectricity ensures the harvesting of energy from the varied ambient, wideband vibration sources for wireless autonomous sensor systems. In the reported studies, a piezoelectric energy harvester (PEH) with high strain concentration and multimodal characteristics plays an important role in enhancing the harvester's vibration amplitude, performance, and frequency bandwidth. This paper proposes a novel multimodal piezoelectric energy harvester by taking advantage of multimodal techniques consisting of a reversed exponentially tapered beam (Primary beam) and six branched beams (Secondary beam) attached to the primary beam’s free end with a proper flange. This design provides wideband with closely placed vibration modes while the reversed exponentially tapered beam attached to the secondary beams configuration provides higher strain distribution and hence improved harvested power. The harvester is subjected to continuous transverse vibrations due to vertical sinusoidal base excitation of varying frequencies and acceleration ranges. As a result, the primary beam with the piezoelectric patch continually deforms and generates electrical energy. The harvester’s theoretical model was developed and derived from the Euler–Bernoulli beam theory. The proposed harvester was fabricated, and its performance evaluated through experimentation at frequencies ranging from 8 to 30 Hz. Experimental results and numerical simulations using COMSOL Multiphysics confirmed the accuracy of the proposed theoretical model. As ambient vibrations were available in a band of frequencies, the proposed multimodal harvester had the potential to capture energy from wideband ambient vibration sources and hence was advantageous over conventional single-mode harvesters in sourcing low-power autonomous sensors. An energy management system designed after investigating the charging behavior of the capacitor with the harvester revealed that the proposed harvester was suitable for source wireless autonomous sensor systems.

Hard coatings, in particular TiN, are widely used as coatings for cutting tools and in the agri-food industry. In the literature, however, few characterizations of hard coatings can be found which define the minimum applied load when the coating starts to fail. In the present study TiN coating was deposited on stainless steel X2CrNi18-9. Vickers and Brinell indentation tests with a wide load range were performed. The main results revealed that the increase of the applied load in Vickers and Brinell indentation influenced the coating and coating/substrate damage evolution. SEM investigation of the Vickers indentation area shows five modes of damage: inclined cracks, radial cracks, lateral cracks, edge cracks, and shear steps. Each damage mode occurs at a specific load range. Parallel cracks already appeared at the edges of the indents at the lowest load of 2 N. For Brinell indentation, cracks start in the coating only at loads higher than F = 307 N. The SEM examinations present damage modes such as circumferential cracks in the border and additional circular cracks in the center of the indent, creating a crack network. Numerical simulations of Brinell indentation were carried out in order to determine the stress distribution in the indent. The comparison of the numerical simulation results with the experimental findings revealed that the coating started to fail at a stress range above 5735 MPa which corresponds to a normal load range of higher than 307 N in Brinell indentation tests. At a load of 613 N cracks were observed.