三重周期极小曲面夹芯结构的隔声性能研究

极小曲面夹芯结构具有高比刚度、良好吸能等优点,在实际工程中展现了广泛的应用前景,而其隔声性能并未得到充分的研究.基于此,利用数值分析和试验方法研究了 D型和I-WP型三重周期极小曲面夹芯结构的隔声性能.首先,基于声振耦合理论,建立极小曲面夹芯结构有限元模型;然后使用声阻抗管法验证了有限元模型的精度;最后,利用验证后的有限元模型系统分析了夹芯厚度、面板厚度、弹性模量、极小曲面常数和周期常数等重要参数对极小曲面夹芯结构隔声性能的影响.研究发现I-WP型极小曲面夹芯结构在4400Hz-5000Hz频段,隔声量可达60dB.本研究有望为高速列车等领域轻质结构被动隔声提供新的解决方案.     

基于Abaqus的光学胶动态力学行为分析

黏胶的动态力学性能对终端产品可靠性的影响越来越重要.基于Abaqus的超弹性和黏弹性的本构模型定义光学胶的动态力学参数,用Abaqus/Explicit对静态压缩和落球试验进行仿真分析,通过与实际试验结果的对比验证仿真分析结果.结果表明,在准静态到高应变率的范围内,采用超弹性和黏弹性的本构模型可以准确描述光学胶的动态力学行为.     

一种新型多孔金属制备方法及缓冲吸能性能研究

多孔金属材料是一种比密度小、比刚度强、吸能效果好的理想型功能材料,因此一直是国内外众多学者研究的热点。文章提出了一种以立方体为基本单元的多孔金属制备方法,为研究其作为吸能材料的力学性能,对制备样品进行了准静态和动态的冲击实验,根据实验结果进行了相应的分析和总结,从而验证了该制备方法的可行性,拓展了多孔金属材料的种类范围,也为进一步优化该多孔金属的制备方法和工艺提供了实验基础。     

Terfenol-D高频磁滞特性测试与分析

目前对超磁致伸缩材料Terfenol-D的研究,主要集中于静态或准静态条件下的磁滞特性的测试和分析.为了更好的探究材料的高频磁滞特性,将Terfenol-D制成方形环状薄片样品,在不同驱动磁场频率和磁密幅值的条件下,测量其动态磁滞回线,分析磁损耗的数值和变化趋势,探究剩磁和矫顽力等磁特性参数随频率和磁密幅值的变化规律.测试结果表明:当驱动磁场频率或磁密幅值增加时,动态磁滞回线横向变宽、面积增大,剩磁、矫顽力和损耗也都随之增大.此项研究为超磁致伸缩材料Terfenol-D高频磁滞特性和电磁损耗的理论分析提供了实验数据基础.     

机器人单足系统-沙土塑性接触力学建模及验证

为了更好地实现足式移动机器人在柔软流动性地面的仿真以及反馈控制,提出了机器人单足系统与沙土(柔性地面环境)接触力学的模型.该模型讨论并继承了部分经典土力学中极限承载力理论的假设条件,并加以拓展和深化,分别建立了机器人硬质足、柔性足与沙土环境的接触力学模型.与其他模型相比,该模型充分考虑了接触面和滑裂面的外形特征,且参数均为常用已测物理参数而不需要在线的辨识过程.设计、加工并搭建了机器人单足式移动平台,完成了单足系统移动平台与沙土环境准静态和动态冲击状态下的相互作用实验.实验和仿真预测结果的对比表明,预测结果与样本数据结果的总误差为8.97%,验证了塑性接触力学模型的准确性和预测足地接触变形时力学行为的有效性.     

负泊松比超材料减振结构设计与实验验证

旋转机械的转子部件发生故障时,振幅会迅速增大甚至发散,此时需要一种轻质高效的吸能减振结构,快速控制转子部件的振动幅值.本文基于负泊松比材料概念,提出了一种针对转子系统的负泊松比弧形超材料减振结构,可以实现很好的故障转子减振效果.首先,通过释放自由度提出了了负泊松比非对称星形胞单元,设计了针对转子的超材料减振结构,并给出了相应的能量吸收指标.然后,基于有限元模型进行了动力学仿真,讨论了不同冲击速度、不同冲击角度对能量吸收性能的影响.结果表明,低速冲击下,材料主要产生弹性变形吸能.随着冲击速度增加,材料变为弹塑性变形混合吸能模式,有效吸能率会明显增大.特别是在冲击速度较大时,减振结构的吸能率会迅速增加,这对于转子突发故障的减振十分有利.最后,设计了验证实验,对故障转子进行了负泊松比减振结构的验证实验.实验结果证明,对于转子的不平衡故障响应,设计的减振结构能够起到很好的抑制转子振动与吸收振动动能效果.     

一种柔性隔振结构的动力学分析及设计方法

本文提出了一种新型的柔性隔振结构,该结构是基于柔性曲梁的力学特性而设计的.研究结果表明,该结构能通过轴向方向的负载来降低扭转方向的刚度,从而达到扭转方向的准零刚度特性,实现低频隔振.本文首先构建了柔性隔振结构的单元模型,并确定了单元模型轴向及扭转方向等关键静力特性,结果表明,该结构的单元模型能实现扭转方向的准零刚度特性,且轴向方向有较高的负载.然后,对不同结构参数的单元模型进行了动力学分析,确定了各结构参数对该结构动力学特性的影响,并利用有限软件对其进行了仿真分析,结果表明,该单元模型具有较好的隔振效果.最后,对构建的多层仿生柔性结构的隔振效率及隔振带宽进行了探讨.该结构具有柔性机构免装配、可整体加工、易小型化等特点,适用于精密光学仪器、机器人、卫星等具有扭转方向低频隔振的领域.     

多稳态力学超材料带隙特性及调控研究

多稳态力学超材料具有多重稳定状态和几何重构特性,在变形吸能和能带调控等方面有重要的研究价值.本研究提出了一种多稳态力学超材料.该超材料是由具有双稳态特性的曲杆和相关实体支撑结构组成.结合有限单元法和布洛赫定理,计算了结构的能带结构,分析了不同稳态条件下结构的带隙特性,得到了几何参数对结构带隙的影响规律,并研究了由5×5个单胞组成的阵列结构中部分单胞变形时,整体结构的传输率.研究发现：双稳态连杆的变形状态可显著改变结构的带隙,尤其是在低频范围内产生了更宽的带隙.整体结构中局部一行或一列单胞变形即可在该方向对应带隙频率范围内实现弹性波传播的衰减.     

碳纤维层合板冲击吸能有限元模拟

为预测复合材料结构的冲击吸能效果,用三维有限元法模拟金属圆柱体冲击碳纤维层合板的过程．层合板被简化为三维正交各向异性材料板;采用Abaqus提供的vumat等扩展编程接口,用FORTRAN编写程序表征材料的弹性、强度和累积失效,实现动态破坏过程仿真;计算结果与冲击试验结果具有可比性．Abaqus的显式分析方法结合编程接口可用于层合板的冲击吸能仿真,结果的准确性取决于用户建立的材料模型．对不同速度、质量和直径的金属圆柱体的冲击进行计算,结果表明在穿透情况下,随着圆柱体速度的增加,圆柱体的动能衰减增多,而系统动能的减少相对稳定,因此后者更适合于临界速度的计算．     

蜂窝结构等效电磁模型的比较与改进

蜂窝结构是吸波材料中广泛使用的一种结构,但其复杂的几何结构给其电磁特性分析与设计带来了一定的困难.采用强扰动理论和变分法的两种等效模型与实验结果进行对比,分析了两种模型中横向等效电磁参数的对称性与实验结果中的非对称性方面存在的显著差异,并通过引入代表蜂窝结构横向非对称性参数的方法对等效电磁模型进行了改进.数值仿真表明,在使用等效电磁模型来描述蜂窝结构时,变分模型要优于强扰动模型,而改进模型不仅使得两种等效电磁模型都能够反映出蜂窝结构横向电磁参数的非对称性,而且能够在一定程度上提高等效电磁模型的准确性.     

Metamaterial band theory： fundamentals ＆ applications

Remarkable progress has been made over the past decade in controlling light propagation and absorption in compact devices using nanophotonic structures and metamaterials. From sensing and modulation, to on-chip communication and light trapping for solar cells, new device applications and opportunities motivate the need for a rigorous understanding of the modal properties of metamaterials over a broad range of frequencies. In this review, we provide an overview of a metamaterial band theory we have developed that rigorously models the behavior of metamaterials made of dispersive materials such as metals. The theory extends traditional photonic band theory for periodic dielectric structures by coupling the mechanical motion of electrons in the metal directly to Maxwell＇s equations. The solution for the band structures of metamaterials is then reduced to a standard matrix eigenvalue problem that nevertheless fully takes into account the dispersive properties of the constituent materials. As an application of the metamaterial band theory, we show that one can develop a perturbation formalism based on this theory to physically explain and predict the effect of dielectric refractive index modulation or metallic plasma frequency variation in metamaterials. Furthermore, the metamaterial band theory also provides an intuitive physical picture of the source of modal material loss, as well as a rigorous upper bound on the modal material loss rate of any plasmonic, metamaterial structure. This in turn places fundamental limits on the broadband operation of such devices for applications such as photodetection and absorption.     

孔隙表征参数驱动的TPMS多孔结构建模

为了设计符合工程设计参数要求的多孔结构模型,提出一种孔隙表征参数驱动的多孔结构建模思路,并以增材制造制备成形.首先,针对三周期极小化曲面(TPMS)的4种常用类型(P/D/G/I-WP),研究了TPMS数学参数对各类孔隙表征参数(孔隙率、比表面积和孔径大小)的影响,并建立了相关参数之间的映射关系模型;接着,提出了若干基于孔隙表征参数的TPMS多孔结构设计方法,包括单设计参数法、多设计参数法、嵌套设计法;最后,给出了相关的工程应用案例并进行Micro-CT测试实验.实验结果表明,所设计模型的孔隙表征参数可控,增材制造成形的模型样件受工艺影响,其精度存在一定偏差.     

骨组织支架的计算机辅助设计方法综述

随着先进的计算机辅助设计和增材制造技术的快速发展,使得制造具有复杂几何结构的骨组织支架成为可能。根据骨组织支架功能设计要求,从几何形态的角度出发将其结构分为规则性多孔结构和不规则多孔结构两大类,并综述了骨组织支架的设计方法,特别强调了两种适合增材制造的设计方法,即三周期极小曲面(TPMS)和拓扑优化。针对骨组织支架结构设计面临的技术挑战,展望了骨组织支架设计方法的可能发展趋势。     

隧道洞口上方危岩崩塌块石运动规律及其对隧道的危害

为揭示危岩崩塌块石的运动规律及其对下方隧道洞口的危害,以都香高速昭通段乐红隧道洞口高陡边坡危岩区崩塌体为研究对象,运用理论计算与Rockfall数值计算2种形式对危岩区崩塌体失稳后块石的运动特征进行预测,运用Abaqus有限元软件模拟不同初速度、不同冲击落点下块石冲击隧道结构的动力响应,揭示不同因素对块石冲击隧道结构的影响程度.结果 显示:理论计算与Rockfall数值计算结果吻合,崩塌块石经坠落、碰撞、滚动最终会与隧道引洞段上表面发生碰撞;与冲击落点相比,块石初速度对隧道结构的动力响应特性影响更大;块石冲击落点位于隧道圆拱圆心正上方位置时对隧道结构的损伤最大;不同冲击落点对碰撞回弹后块石的速度影响不大.     

Design of buckling-induced mechanical metamaterials for energy absorption using topology optimization

A novel design concept for buckling-induced mechanical metamaterials for energy absorption is presented. The force-displacement curves of the mechanical metamaterials are analyzed according to the curves of their unit cells, and the energy-absorbing characteristics of mechanical metamaterials are evaluated. Two topology optimization models are proposed. One maximizes the buckling-induced dissipated energy to facilitate the design of metamaterials with high energy absorption and low elastic strain energy. The other maximizes the dissipated energy with a constraint that the mechanical metamaterials should be self-recoverable. An energy interpolation scheme is employed to avoid numerical instabilities in the geometric nonlinear finite element analysis. A two-phase algorithm is proposed to find the optimized result from a uniform initial guess, and sensitivity analysis is performed. The optimized design has a larger amount of buckling-induced dissipated energy than the previously proposed structural prototypes. Moreover, the self-recoverable mechanical metamaterial is successfully designed by topology optimization.     

Modeling of the incudo-malleolar joint within a biomechanical model of the human ear

Under large quasi-static loads, the incudo-malleolar joint (IM joint), connecting the malleus and the incus, is highly mobile. It can be classified as a mechanical filter decoupling large quasi-static motions while transferring small dynamic excitations. To investigate the influence of the behavior of the IM joint, a detailed simulation model of the IM-complex is created. Mathematical modeling of the IM joint behavior under quasi-static excitation requires adequate modeling of the mechanics of the diarthrodial joint. Therefore, the geometry of the articular surfaces, the ligaments, as well as their viscoelastic properties have to be included in the model. The contact of the articular surfaces is implemented using a penalty based contact formulation utilizing the geometric information obtained from micro computer tomography (micro-CT) scans. The ligaments of the joint capsule are modeled by distributing force elements along the joint capsule, with the position and orientation derived from the micro-CT scans. It is shown that the effects which were observed in measurements on human temporal bones are described adequately by the model, if the contact of the articular surfaces and the preload of the viscoelastic fibers are taken into account in the simulation model. In the following, the detailed model is implemented in an elastic multibody system of the entire ear. The model allows the study of different quasi-static load cases of the ossicles, such as it occurs in the reconstruction of the middle ear and form the basis for future simulative studies of sound transmission in natural or reconstructed ears.     

Multiscale hydro-thermo-mechanical model for early-age and mature concrete structures

Temperature and early-age mechanical properties in hydrating concrete structures present a significant risk for cracking, having a major impact on concrete durability. In order to tackle these phenomena, a multiscale analysis is formulated. It accounts for a high variety of cement properties, concrete composition, structure geometry and boundary conditions.The analysis consists of two steps. The first step focuses on the evolution of moisture and temperature fields. An affinity hydration model accompanied with non-stationary heat and moisture balance equations are employed.The second step contains quasi-static creep, plasticity and damage models. It imports the previously calculated moisture and temperature fields into the mechanical problem in the form of a staggered solution. The whole model has been implemented in the ATENA software, including also the effect of early-age creep, autogenous and drying shrinkage.Validation on selected structures shows a good prediction of temperature fields during concrete hardening and a reasonable performance of the mechanical part.     

多孔金属纤维烧结板多尺度形貌的快速三维建模

针对多孔金属纤维烧结板这一新型功能材料的多尺度形貌建模问题,基于机械加工表面微观形貌中存在的自仿射分形特性,拓展前期发展的Triply Periodic Minimal Surface（TPMS）周期曲面与Weierstrass-Mandelbrot（W-M）分形几何快速合成方法,重点根据多孔金属纤维烧结板的结构特点,对Marching Cubes算法进行优化,以更高效地建立烧结板三维多尺度形貌的几何模型;同时,引入参数表征方法驱动分形TPMS对烧结板的形貌进行调整与控制.实例分析结果表明,提出的方法可更有效地建立/控制PMFSF的多尺度形貌模型;模型的有效性通过数值仿真和与其它方法的比较得到了验证.该建模方法可直接用于其它具有多尺度形貌的功能材料的数字化设计,并促进其数值模拟技术的发展.