International Journal of Mechanics and Materials in Design最新文献

In this study, an iterative design window (DW) search using nonlinear dynamic simulation was proposed for polymer micromachined flapping-wing nano air vehicles (FWNAVs) that can satisfy both nonlinear and unsteady design requirements, which are contradictory to each other. The DW is defined as an existing area of satisfactory solutions in the design parameter space. The present FWNAVs have a complete 2.5-dimensional structure such that they can be fabricated using polymer micromachining. The micro-wing of our FWNAVs has been designed using morphological and kinematic parameters of an actual dipteran insect. Finally, using our method, we found the DW that allowed miniaturization of the design down to 10 mm while satisfying all the design requirements. Our findings demonstrate the possibility of further miniaturizing FWNAVs down to the size of small flying insects.

The type and distribution of microstructure of metallic materials in laser additive manufacturing have an important influence on the overall mechanical properties, and how to control the location distribution of microstructure rationally through topology optimization to improve the mechanical properties of the part is one of the research focuses. In this paper, we propose a method of microstructure distribution and orientation-structure topology optimization (MDOSTO) for laser additive manufacturing. This method obtains the position distribution of the microstructure of columnar and equiaxed grains under a macroscopically optimised design. Based on the anisotropy of columnar crystals and the isotropy of equiaxed grains to obtain a microstructure with alternating grains distribution for optimal mechanical properties. The flexibility is compared with the structure of disordered grain distribution by two arithmetic examples (Miniature binding beam and Cantilever Beam), and the flexibility is reduced by 26.3% and 26.6%, respectively, which verifies the feasibility and effectiveness of the method. This method makes full use of the properties of different microstructures to improve the mechanical properties of the part.

In this work, novel four-unknown refined theories were used to evaluate the free vibration of rotating stiffened toroidal shell segments subjected to varying boundary conditions in thermal environments. The shell segments consist of a functionally graded graphene-platelet-reinforced composite (FG-GPLRC). The effective material properties of the composite were calculated using the modified Halpin–Tsai model and the mixture rule. The governing equations of motion for the shell were formulated within the novel four-unknown refined shell theory framework. The effects of centrifugal and Coriolis forces and the initial hoop tension resulting from rotation were all included. The Rayleigh–Ritz procedure and smeared stiffener technique were subsequently used to determine the natural frequencies of the shells with stiffeners. The advantages of the adopted shell theory result directly from the reduction of key unknowns without the need for the shear correction factor, and it can predict better results for FG-GPLRC structures. Finally, numerical examples were provided to validate the proposed solution and demonstrate the effects of four-unknown refined theories, material distribution patterns, boundary conditions, rotating speed, and temperature rise on the natural frequencies of toroidal shell segments.

The piezoelectric sensor in the structural health monitoring (SHM) system may be debonded due to complex service environment. However, there are little attention on the debonding behavior of piezoelectric element, which could affect the reliability of the monitoring network. This paper considers the effect of left and right debonding of sensor on receiving signal with different debonding length (2, 4, 6 and 8 mm, respectively) and debonding directions (which are 90°, 180° and 270°, respectively). A finite element model was established to simulate the interface debonding between piezo disc and Aluminium matrix, and both an experimental investigation using a real Aluminium plate is made to further comparison with the simulation results. The characteristic parameters including the amplitude and phase of time domain receiving Lamb wave signals were extracted. The simulation results show the voltage distributions of piezoelectric sensor under different debonding length and direction. In addition, receiving signal indicates that there is not a monotonic downward trend of signal amplitude with the increase of right debonding length of the sensor. And when the wave propagation direction is parallel to the sensor debonding direction (180°), the signal amplitude of the sensor is greater than that perpendicular to the debonding direction (90° and 270°).

It has a positive impact on the machining accuracy to predict precisely the thermal error caused by the temperature change for the high-speed spindle-bearing system. In this paper, the dual reciprocity method (DRM) based on compactly supported radial basis functions (CSRBFs) and the line integration boundary element method (LIM-BEM) are presented for the thermal-deformation coupling calculation. The essential idea of this method is building the thermal-deformation coupling model only by the boundary information and obtaining results by line integrals. In this process, the boundary element model discretized by the discontinuous iso-parametric quadratic boundary element is established. Then, the transient temperature is calculated by the CSRBFs-DRM, and the thermo-elastic deformation is done by the LIM-BEM, under the exact calculation of the heat generation and the thermal contact resistance. To validate the effectiveness, thermal-deformation coupling experiments are conducted. The proposed method is compared with experimental data and the finite element method. The result shows that the proposed model is more appropriate for the thermal-deformation coupling calculation for the satisfactory universality and accuracy.

As an essential step of product design, tolerance design plays a critical role in reducing manufacturing costs while ensuring mechanical assemblies’ quality and reliability. However, existing tolerance allocation approaches only are concentrated on design specification constraints during the design stage, although component degradation caused by environmental and operating conditions increases the probability of product failure during the service life. To deal with the degradation effect arising over the service life of mechanical assemblies, this paper proposes a reliability-based tolerance design approach to allocate optimal, reliable tolerances to mechanical systems. The proposed approach rewrites the tolerance allocation problem as a two-objective optimization problem with probabilistic constraints, where time-dependent reliability is incorporated to ensure the product’s reliable and consistent operation during the specified service life. Then, the proposed approach applies the non-dominated sorting genetic algorithm II and an entropy-based TOPSIS method to obtain the non-dominated optimal tolerances and the best solution, respectively. In addition, unlike previous methods, epistemic uncertainty effects are considered in this work. A modified linear degradation model is developed to include the epistemic uncertainty in the degradation model’s parameters and investigate the effects of uncertainties on reliability.Accordingly, the proposed approach employs a single-loop sampling procedure to incorporate the effects of epistemic uncertainty on the obtained optimal tolerances. Finally, to illustrate the capability of the proposed method, an industrial case study is considered, and the obtained results and performances are compared and discussed.

In this paper, the multi-objective optimization design of arc star honeycomb (ASH) and bi-directional reentrant honeycomb (BRH) is carried out by Python script to improve Young's modulus based on the lightweight of the honeycomb. A large number of models of different structural parameters are established by the Python script and analyzed by the finite element method, and then the response surface model (RSM) is established according to the results of finite element analysis. On this basis, the non-dominated sorting genetic algorithm (NSGA-II) and RSM are combined to perform multi-objective optimization of the 2D and 3D configurations of the two types of honeycomb, and the optimal set of parameters is selected by comparing the individual fitness values. The results show that after multi-objective optimization, Young's modulus of the ASH and BRH is enhanced in both 2D and 3D configurations with the smallest possible mass. In addition, the ASH has performance advantages over the BRH in 2D configuration, and BRH is better in 3D configuration. It can also be observed that the ASH and BRH have Poisson ratio adjustable properties. The results also show that this multi-objective optimization method can effectively save the analysis and calculation time. The lightweight, high-strength metamaterial is expected to be used in key fields such as aerospace.

This study focuses on the electromechanical study of functionally graded graphene reinforced piezoelectric composite (FG-GRPC) structures using the modified Halpin Tsai (MHT) micromechanics model. Two piezoelectric material matrices, namely PZT-5H and PVDF, are reinforced with GPLs, an ultralightweight and highly rigid carbonaceous nanofiller. The developed graphene reinforced piezoelectric composites (GRPC) vary in the thickness direction to form FG-GRPC, with GPLs evenly scattered throughout the material matrix. The MHT model and Rule of the mixture (ROM) are used to determine the effective modulus of elasticity, poisson’s ratio, density, and piezoelectric characteristics of the GRPC structure. The spatial variation in composition across the thickness of FG-GRPC structural tiles is determined by a simple power law distribution. The voltage and power metrics of a circuit are calculated using first order shear deformation theory and Hamilton's approach from the governing differential equations of motion. An exhaustive parametric study is undertaken with an emphasis on the effects of GPL weight percentage, material grading exponent, thickness ratio, and frequency on the circuit metrics of FG-GRPC structures. Our findings indicate that the material grading exponent and a limited number of GPLs considerably improve the circuit parameters of FG-GRPC tiles. This study will demonstrate the required physical insights for coupled modelling of microelectromechanical systems, with applications spanning pressure sensors, small ultrasonic motors, active controllers, and intelligent systems.

The concentration of the present investigation is on the development of a quadrilateral shell element for the deformation analysis of composite laminates. For this purpose, a higher-order shell model with 12 parameters is adopted along with the three-dimensional state of stress. The principle of virtual work is implemented to derive the stiffness matrix and the load vector for the four-node shell element. In order to verify the performance of the higher-order shell element developed herein for the treatment of laminated composites, some benchmarks are solved and compared with solutions available in the literature.

Supercritical transmission shafts, which have one or more critical speeds below their working speeds, are becoming more popular in new rotorcraft designs. To attenuate the excessive transcritical vibration, dry friction damper is a prevailing choice. In this paper, we focus on the basic working mechanism and parameter influence of the dry friction damper for supercritical transmission shaft. Mathematical model of the dry friction damper, which fully considers the nonlinear rub-impact and side-dry-friction effects, is proposed and integrated with finite element model of the transmission shaft to investigate nonlinear interactions between the shaft and damper. It is demonstrated through systematic numerical simulations that a typical transcritical response with dry friction damper can be divided into 4 sub-regions and the dry friction damper takes effect only within region II and III respectively through hard-stopping and side-dry-friction effects. In addition, effects of nonlinear bearing force, transcritical acceleration and initial location of the damper are discussed in detail. Moreover, influences of 3 key damper parameters, that is the rub-impact clearance, the critical slip force and the circumferential friction coefficient, are further investigated, which provides a guidance for designs of the dry friction damper. Finally, prototypes of the dry friction damper are designed, manufactured and tested on a rotor dynamics test rig. For the first time, the theoretical analysis and numerical simulation results are quantitatively verified by an experiment.