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A new hybrid lattice structure with improved modulus,strength and energy absorption properties

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Science China(Technological Sciences) 2023年第7期66卷 2119-2133页

作者： LI LingBo YANG Fan WANG Peng GUO ZhengMiao School of Aerospace Engineering and Applied Mechanics Tongji UniversityShanghai 200092China

In this paper,a hybrid octagonal simple-cubic(OSC) lattice structure is obtained by combining the cell configurations of the bending-dominated octagonal lattice and the stretching-dominated SC lattice.Finite element(FE) numerical models of the three lattice structures(octagonal,octet and OSC lattice) are established and the axial quasi-static compression simulations are performed.In addition,a theoretical model is established to predict the plateau stress of the OSC lattice with different volume coefficients k.Satisfactory consistency is achieved between the results of the theoretical model and those from FE numerical simulations.The results show that the elastic modulus,the compression strength and the energy absorption capacity of the proposed OSC lattice are respectively increased by 233%,86%,and 25% compared with the octagonal lattice under the same relative density conditions,while those values are respectively 212%,34%,and 20% compared with the octet lattice,highlighting the superior mechanical properties of the hybrid OSC lattice.The effects of volume coefficient k and loading direction on the compression behavior of the OSC lattice were parametrically analyzed.The results show that the volume coefficient k is inversely related to the mechanical properties,and an anisotropic characteristic is exhibited in terms of the compression behavior of the OSC lattice structures.

关键词： lattice structure energy absorption hybrid structure mechanical properties anisotropy

Wrinkling in graded core/shell systems using symplectic formulation

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applied Mathematics and mechanics(English Edition) 2023年第12期44卷 2057-2070页

作者： Yaqi GUO Guohua NIE School of Aerospace Engineering and Applied Mechanics Tongji UniversityShanghai 200092China

Wrinkles in flat graded elastic layers have been recently described as a timevarying Hamiltonian system by the energy method.Cylindrical core/shell structures can also undergo surface instabilities under the external pressure.In this study,we show that by treating the radial direction as a pseudo-time variable,the graded core/shell system with radially decaying elastic properties can also be described within the symplectic framework.In combination with the shell buckling equation,the present paper addresses the surface wrinkling of graded core/shell structures subjected to the uniform external pressure by solving a series of ordinary differential equations with varying coefficients.Three representative gradient distributions are showcased,and the predicted critical pressure and critical wave number are verified by finite element simulations.The symplectic framework provides an efficient and accurate approach to understand the surface instability and morphological evolution in curved biological tissues and engineered structures.

关键词： wrinkling graded core/shell system symplectic analysis gradient distribution

Theoretical study on dynamic effective electroelastic properties of random piezoelectric composites with aligned inhomogeneities

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applied Mathematics and mechanics(English Edition) 2023年第4期44卷 525-546页

作者： Yanpeng YUE Yongping WAN School of Aerospace Engineering and Applied Mechanics Tongji UniversityShanghai 200092China

The closed-form solutions of the dynamic problem of heterogeneous piezoelectric materials are formulated by introducing polarizations into a reference medium and using the generalized reciprocity theorem.These solutions can be reduced to the ones of an elastodynamic problem.Based on the effective medium method,these closedform solutions can be used to establish the self-consistent equations about the frequencydependent effective parameters,which can be numerically solved by iteration.Theoretical predictions are compared with the experimental results,and good agreement can be found.Furthermore,the analyses on the effects of microstructure and wavelength on the effective properties,resonance frequencies,and attenuation are also presented,which may provide some guidance for the microstructure design and analysis of piezoelectric composites.

关键词： piezoelectric composite dynamic effective property self-consistent method resonance frequency wavelength

Effects of time-delayed vibration absorber on bandwidth of beam for low broadband vibration suppression

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applied Mathematics and mechanics(English Edition) 2023年第10期44卷 1629-1650页

作者： Xiuting SUN Yipeng QU Feng WANG Jian XU School of Aerospace Engineering and Applied Mechanics Tongji UniversityShanghai 200092China

The effects of time-delayed vibration absorber(TDVA) on the dynamic characteristics of a flexible beam are investigated. First, the vibration suppression effect of a single TDVA on a continuous beam is studied. The first optimization criterion is given,and the results show that the introduction of time-delayed feedback control(TDFC) is beneficial to improving the vibration suppression at the anti-resonance band. When a single TDVA is used, the anti-resonance is located at a specific frequency by the optimum design of TDFC parameters. Then, in order to obtain low-frequency and broad bands for vibration suppression, multiple TDVAs are uniformly distributed on a continuous beam,and the relationship between the dynamic responses and the TDFC parameters is investigated. The obtained relationship shows that the TDVA has a significant regulatory effect on the vibration behavior of the continuous beam. The effects of the number of TDVAs and the nonlinearity on the bandgap variation are discussed. As the multiple TDVAs are applied, according to the different requirements on the location and bandwidth of the effective vibration suppression band, the optimization criteria for the TDFC parameters are given, which provides guidance for the applications of TDVAs in practical projects such as bridge and aerospace.

关键词： time-delayed vibration absorber(TDVA) time-delayed feedback control(TDFC) parameter design criterion broadband vibration suppression

Nonlinear Bending of FCC Nanoplates Based on a Quasi-Continuum Model

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Acta Mechanica Solida Sinica 2022年第6期35卷 1030-1039页

作者： Wenjing Zhan Yaqi Guo Ying Zhao Guohua Nie School of Aerospace Engineering and Applied Mechanics Tongji UniversityShanghai200092China

A quasi-continuum model of plate-type nanomaterials with the face-centered cubic crystal structures is proposed in this paper.The fundamental governing equations for the nonlinear bending of the nanoplates are given by using the principle of minimum potential energy.Specifically,the analytical solution is derived for cylindrical bending deformation of the structure under uniform transverse loading fixed at two sides based on the modified iterative method.A lattice finite element model is established to verify the present quasi-continuum model.Meanwhile,the corresponding solution by adopting the classical continuous plate theory is presented,in which two cases are considered for use of bulk values(limit values)and nanovalues of both elastic modulus and Poisson's ratio.The difference among the quasi-continuum and continuous models are discussed by computation.

关键词： FCC Nanoplates Quasi-continuum model Size effect Nonlinear bending

The Improved Interpolating Complex Variable Element-Free Galerkin Met hod for Two- D imensional Elastic Problems

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Acta Mechanica Solida Sinica 2022年第2期35卷 328-343页

作者： Yajie Deng Ying Dai School of Aerospace Engineering and Applied Mechanics Tongji UniversityShanghai 200092China

An improved interpolating complex variable element-frees Galerkin(IICVEFG)method for the two-dimensional elastic problems is developed.This method is based on the improved interpolating complex variable moving least-squares(IICVMLS)method and the integral form of the elastic problems.In the IICVEFG method,the proposed shape function has the interpolating feature.Therefore,the essential boundary conditions can be exerted directly.Additionally,the unnecessary t erms in the discrete mat rices are removed,which resul ts in a set of concise formulas.This method is verified by analyzing three elastic examples under different constraints and loads.The numerical results show that the IICVEFG method is superior in precision and efficiency to other non-interpolating meshless methods.

关键词： Interpolating meshless met hod Elastic problems Singular weight function Complete basis function

Exact analysis of the orientation-adjusted adhesive full stick contact of layered structures with the asymmetric bipolar coordinates

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applied Mathematics and mechanics(English Edition) 2022年第6期43卷 883-898页

作者： Pengxu GUO Yueting ZHOU School of Aerospace Engineering and Applied Mechanics Tongji UniversityShanghai 200092China

The adhesion failure has become one dominant factor in determining the reliability and service life of miniaturized devices subject to loadings with arbitrary orientations.This article establishes an adhesive full stick contact model between an elastic half-space and a rigid cylinder loaded in any direction.Using the Papkovich-Neuber functions,the Fourier integral transform,and the asymmetric bipolar coordinates,the exact solution is obtained.Unlike the Johnson-Kendall-Roberts(JKR)model,the present adhesive contact model takes into account the effects of the load direction as well as the coupling of the normal and tangential contact stresses.Besides,it considers the full stick contact which has large values of the friction coefficient between contacting surfaces,contrary to the frictionless contact supposed in the JKR model.The result shows that suitable angles can be found,which makes the contact surfaces difficult to be peeled off or easy to be pressed into.

关键词： contact mechanics adhesion friction Johnson-Kendall-Roberts(JKR)model Fourier integral transform exact solution

硬/软复合材料结构防爆性能的实验及数值评估

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Acta Mechanica Sinica 2022年第1期38卷 27-36页

作者：杨丰源栗志杰庄茁柳占立 applied mechanics Laboratory Department of Engineering MechanicsSchool of AerospaceTsinghua UniversityBeijing 100084China

现实防护工程中,硬1软复合结构在人员装甲(如头盔的外壳/衬里系统)中的应用可以有效减轻爆炸伤害.由于缺乏有效可靠的实验方法评估防护结构的防爆性能,直接接触型防护结构的发展受到限制,本文针对硬/软复合材料结构的防爆性能测试提出... 详细信息

现实防护工程中,硬1软复合结构在人员装甲(如头盔的外壳/衬里系统)中的应用可以有效减轻爆炸伤害.由于缺乏有效可靠的实验方法评估防护结构的防爆性能,直接接触型防护结构的发展受到限制,本文针对硬/软复合材料结构的防爆性能测试提出一种新的实验及数值评估方法,并对其防爆机理进行了分析.受测的硬/软结构由超高分子量聚乙烯(UHMWPE)复合材料和膨胀聚乙烯(EPE)泡沫组成.现场爆炸试验通过7.0 kg TNT球形炸药在3.8 m处产生的爆炸波来完成.设计了一种压力测试装置用于支撑被测结构并测量穿透防护结构的爆炸压力脉冲.实验结果表明,通过使脉冲波形更平坦、减小压力幅度和延迟脉冲到达时间,硬/软结构可以将爆炸压力脉冲减弱为三角形压力脉冲.7mmUHMWPE复合材料和20mmEPE泡沫的组合防护结构可将爆炸压力振幅降低40%.通过有限元模拟分析爆炸缓解机制.数值结果表明,爆炸压力脉冲的衰减主要发生在硬/软界面上,通过界面反射压力波和软材料层变形吸收动能来完成.在此基础上提出的理论模型可以很好地解释实验和数值结果,对评价和设计高性能的防爆结构具有重要意义.

关键词：防爆结构防爆性能接触型压力脉冲复合材料结构脉冲到达时间爆炸试验复合结构

Large-eddy simulation of turbulent boundary layer flow over multiple hills

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Journal of Hydrodynamics 2023年第4期35卷 746-756页

作者： Ying Deng Kai Leong Chong Yan Li Zhi-ming Lu Bo-fu Wang Shanghai Key Laboratory of mechanics in Energy engineering Shanghai Institute of Applied Mathematics and MechanicsSchool of Mechanics and Engineering ScienceShanghai UniversityShanghai200072China School of Aerospace Engineering and Applied Mechanics Tongji UniversityShanghai200092China

Atmospheric boundary layer(ABL)flow over multiple-hill terrain is studied numerically.The spectral vanishing viscosity(SVV)method is employed for implicit large eddy simulation(ILES).ABL flow over one hill,double hills,and three hills are presented in detail.The instantaneous three-dimensional vortex structures,mean velocity,and turbulence intensity in mainstream and vertical directions around the hills are investigated to reveal the main properties of this turbulent flow.During the flow evolution downstream,the Kelvin-Helmholtz vortex,braid vortex,and hairpin vortex are observed sequentially.The turbulence intensity is enhanced around crests and reduced in the recirculation zones.The present results are helpful for understanding the impact of topography on the turbulent flow.The findings can be useful in various fields,such as wind energy,air pollution,and weather forecasting.

关键词： Large-eddy simulation(LES) atmospheric boundary layer(ABL)flow complex terrain turbulent flow fields