梯度模式对Miura-ori超材料力学性能影响的研究

Miura-ori超材料是一种重量轻且多孔的材料,其机械性能通常是由自身的折叠方式和几何形状决定的,它的机械响应可以通过几何设计来进行修正调整,是一种具有多功能的、可调控且设计空间多样的超材料。为研究厚度渐变(Thickness Gradient,TG)模式以及锐角渐变模式对超材料能量吸收能力的影响,结合有限元分析软件参数化分析超材料的力学特性。研究结果表明,TG梯度为负梯度的超材料能量吸收能力较好,并且负梯度时的TG梯度超材料的平均力和能量吸收比锐角梯度超材料表现更佳。

堆叠三浦折纸隔振器理论模型及低频隔振特性

低频振动衰减速度慢难以控制,严重影响高端装备的精度、稳定性和可靠性.线性隔振器因承载能力和隔振频带之间的固有矛盾无法有效隔离低频振动.因此,可通过引入非线性获得等效负刚度和非线性刚度构建准零刚度隔振器,以实现低频隔振.折纸结构具有双稳态、负泊松比和负刚度等独特的力学特性,近年来得到了广泛关注.受堆叠三浦折纸(stacked Miura-ori,SMO)启发,提出了一种新型SMO隔振器,由SMO结构和线性弹簧并联构成.基于能量法推导了SMO结构的势能方程,获得了竖直方向的力-位移关系,揭示了SMO结构大行程负刚度机理.研究了无应力条件下不同初始角和折痕刚度比对SMO隔振器的恢复力的影响规律,阐明了SMO隔振器非线性刚度调节机制.建立了SMO隔振器的理论模型,基于谐波平衡法推导了位移传递率.通过数值仿真研究了不同负载下的低频隔振性能.最后研制了SMO隔振器的原理样机,试验验证了SMO隔振器的恢复力和低频隔振性能.结果表明,折纸隔振器峰值频率可低至1.52 Hz,最小峰值传递率为1.29.本研究为低频折纸隔振结构的设计提供了一种新思路.

Deployment of SMP Miura-ori sheet and its application:Aerodynamic drag and RCS reduction

Origami,such as Miura-ori,is the art of folding two-dimensional materials into complex,elaborate,and multifunctional three-dimensional objects.In this paper,SMP MO sheet are prepared,and the accuracy of deployable process is verified by experiments.The folding and deployable process of SMP MO sheet is divided into 4 stages,and each stage is described in detail.The stiffness of smart deployable stage is characterized by an exponential decline at the beginning and a gradual decrease to 0,and this is similar to the theoretical shear equivalent modulus in the Y direction.The effects of various parameters on strain and stress are also explored.The purpose of studying these mechanical characteristics is to provide driving force reference in application;In terms of application,the flow field and electromagnetic characteristics of MO sheet in different directions are studied.The aerodynamic drag and RCS reduction of MO unit cell and graded MO sheet during the deployable process are evaluated.When the dihedral fold angle is about 45°,the RCS reduction and drag reduction characteristics of MO sheet are relatively optimal,which is most beneficial to morphing aircraft.

可展薄膜的Miura弹性折痕建模与分析

为满足空间任务中对可展薄膜机构的大折展比、高平整度等需求,提出基于Miura弹性折痕的空间薄膜可展机构,并进行建模分析及样机研制。根据折痕分布规律和几何关系建立Miura-ori几何模型,研究薄膜的折痕参数对折展比和折痕总长的影响规律,并进行计算和折痕参数优化。在ABAQUS/Explicit中建立折痕倾角θ=90°及θ<90°的四折痕基本单元的数值仿真模型,分析薄膜关键折痕处的力学行为变化,初步证明二维弹性折痕的可行性;进一步研究经过Miura弹性折痕折叠后三角形薄膜的弹塑性,绘制折痕交点处应力随折叠过程的变化曲线,应力峰值均处于材料弹性范围内;研制空间可展开薄膜机构样机,进行了验证分析。结果表明:机构构型设计方案合理,优化后的折痕参数可以得到大折展比和小折痕总长的薄膜Miura折叠方案,展开后薄膜表面具有较高的平整度,证明了可展薄膜Miura弹性折痕的可行性和优越性。

The Compressive and Shear Characteristics of Miura-ori Forms as Core Materials of Sandwich Structures

The mechanical properties of Miura-ori foldcore metamaterials were studied using finite element simulations.The responses of foldcores with various topological parameters to quasi-static out-of-plane compression and shear loading were analyzed using the relative density as a governing parameter.The non-unique relationships between the core density and the materials'strength in the examined loading directions were revealed,pointing out the strong influence of the Miura-ori topology.Linear relationships were established between the elastic moduli and relative densities of the Miura-ori metamaterials while power-law functions of the relative density with different exponent constants were established for the strength in different loading directions.It was shown that the Miura-ori materials possess the highest strength under shear in the X1-X3 plane and it increases with the increase in the relative density.However,this characteristic is strongly influenced by the sector angleα.In general,the difference between the two shear strengths increases when increasing the relative density by using thicker cell walls.It is noted that the strength of the Miura-ori materials as a function of the relative density is nearly constant with respect to the cell dimensions if the values of folding angleγ0 and sector angleαare given.The mechanical characteristics of the Miura-ori material with equal relative density,which exhibits the highest strength among the analyzed origami models,are compared with the out-of-plane compression and shear responses of prismatic hexagonal honeycomb.It is observed that compression and shear responses of the honeycomb outperform the Miura-ori foldcore in all loading directions when considering large deformations.

三浦折纸超材料结构数字化设计与模型验证

折纸结构在航空航天、柔性电子、汽车船舶和建筑结构等领域具有较好的应用前景.三浦折纸单元沿三向拓展可构建出三浦折纸超材料结构,具有高孔隙、可自锁、平面折展、负泊松比、形态可控等特性.为了便于生成折纸超材料结构的复杂三维模型、推广应用于缓冲吸能结构及可展结构,本文利用Matlab和Grasshopper软件,发展了三浦折纸超材料结构的数字化设计方法,利用数字化建模及3D打印技术,实现了零厚度及非零厚度三维折纸模型的统一建模,并开展了物理模型验证分析,探讨了3D打印制作折纸超材料结构模型的优缺点;推导了三浦折纸超材料的折痕长度、相对密度、折叠率等特性与几何参数的关系,利用Abaqus/Explicit软件开展了结构准静态压缩过程分析与验证,揭示相对密度对结构吸能指标的影响规律.研究结果表明,折纸超材料结构数字化设计方法高效、准确,便于结构选型及优化分析,所得三维模型结果与理论值吻合较好.当胞元面板构型、面板厚度及结构折痕总长不变时,相对密度较小的三浦折纸超材料结构具备更为优异的吸能效率.

A geometry-based framework for modeling the complexity of origami folding

This paper presents a quantitative framework to analyze the complexity of folding origami structures from flat membranes.Extensive efforts have realized intricate origami patterns with desired functions such as mechanical properties,packaging efficiency,and deployment behavior.However,the complexity associated with the manufacturing or folding of origami patterns has not been explored.Understanding how difficult origami structures are to make,and how much time they require to form is crucial information to determining the practical feasibility of origami designs and future applications such as robotic origami assembly in space.In this work,we develop this origami complexity metric by modeling the geometric properties and crease formation of the origami structure,from which it outputs crease and pattern complexity values and a prediction of the time to complete the pattern assembly,based on the characteristics of the operator.The framework is experimentally validated by fabricating various Miura-ori origami paper models.

基于三浦折纸电容式压力传感器的仿真与优化

柔性电容式压力传感器的灵敏度通常随压力的增加而衰减,这可能会影响其在具有环境压力情况下的应用。基于三浦折纸结构的柔性电容式压力传感器由于其特殊的折叠方式,可以同时改变电极之间的距离和正对面积来提高电容的相对变化率。本文通过有限元仿真验证了三浦折纸电容式压力传感器的灵敏度随压力的增加而增大的变化规律。此外,仿真了不同初始二面角和厚度的三浦折纸传感器在不同压力下的电容变化情况,从结构上进行性能优化。