组合蜂窝材料面内冲击性能的研究

基于三角形和六边形蜂窝结构面内冲击性能的研究,该文探讨了面内冲击荷载作用下组合Kagome蜂窝结构的变形机制和能量吸收特性。首先,在保证蜂窝结构胞元厚度与边长尺寸比值不变的前提下,分析了不同形状胞元及其组合结构的动态冲击性能,给出了试件宏观及微观胞元结构的动态演化过程。在此基础上,探讨了冲击速度和相对密度一定情况下单位质量不同蜂窝结构的能量吸收特性。其结论将对蜂窝材料微拓扑结构的动力学优化设计提供指导。     

六韧带手性蜂窝结构的动力学响应特性研究

利用显式动力有限元ANSYS/LS-DYNA数值研究了六韧带手性蜂窝结构的面内冲击动力学特性。在保证圆环节点半径不变的前提下,通过改变韧带长度和胞元厚度,首先建立了六韧带手性蜂窝的有限元模型,具体讨论了冲击速度和胞元微结构参数对手性蜂窝材料的面内宏/微观变形行为、密实应变、动态平台应力和比能量吸收能力的影响。研究结果表明,随着冲击速度的增加,六韧带手性蜂窝结构表现为3种宏观变形模态：“> <”型模式、“过渡”模式和“I”型模式。在中、低速冲击载荷下,能够明显观察到拉胀材料在轴向压缩时独特的“颈缩”现象,其主要与韧带绕着圆环中心节点的旋转变形有关。通过引入无量纲“动态敏感因子”,还研究了六韧带手性蜂窝材料的面内动态冲击强化效应。     

构型对正多边形蜂窝异面缓冲性能的影响

目的 利用有限元法研究应变率不敏感的双线性各向同性应变硬化正多边形（等边三角形、正方形、正六边形和正八边形）蜂窝的异面缓冲性能。方法 建立基于正多边形蜂窝特征单元的异面冲击分析有限元模型，提出最佳应变这一缓冲性能评价新指标，基于此重新定义各能量吸收评价指标，形成新缓冲性能评价方法。结果 以此获取不同相对密度的各正多边形蜂窝在不同冲击速度下的变形模式和应力-应变曲线，以及平均平台应力、比能量吸收和冲击力效率等评价指标值，并进行了分析。结论 给定相对密度下，正八边形蜂窝具有最大的异面平均平台应力；正多边形蜂窝的比能量吸收与冲击速度成二次关系；定密度的正六和八边形蜂窝的冲击力效率优于等边三角形和正方形蜂窝。     

三角形蜂窝在面内冲击荷载下的力学性能

摘要：通过数值计算研究规则排布和交错排布的三角形铝蜂窝在面内冲击荷载下的变形模式、承载能力以及能量吸收特性。结果表明两种蜂窝的变形均随着冲击速度的增加或胞壁厚度的减小而向冲击端集中,规则排布的蜂窝沿着局部变形带逐行压溃直至密实,而交错排布蜂窝的变形模式可分为4种。铝蜂窝吸收的能量绝大部分转化为变形所需的内能,动能所占比重较小。随着冲击速度的提高,两种排布方式的蜂窝均表现出更强的承载能力和能量吸收能力,但内能在总能量中的比重减小,动能比重增加。规则排布的蜂窝比交错排布的蜂窝具有更高的承载力和能量吸收能力,该差别主要是由于二者内能的不同所引起,且该差值在交错排布蜂窝“核区”形成后逐渐减小。     

集中缺陷对蜂窝材料面内动力学性能的影响

利用显式动力有限元ANSYS/LS-DYNA数值研究了三角形和四边形蜂窝材料中集中缺陷对其面内冲击性能的影响.研究结果表明,对于集中缺陷,除了缺陷率,缺陷集中区域的位置也是材料设计中需要考虑的重要指标.随着缺陷率的增加,蜂窝材料的平台应力和能量吸收能力迅速降低,但随着冲击速度的增加,缺陷的影响逐渐减弱.缺陷集中区域的位...     

米字形填充正方形蜂窝异面平台应力

目的 研究冲击速度和结构参数对米字形填充正方形蜂窝异面平台应力的影响规律。方法 利用ANSYS/LS-DYNA建立该蜂窝可靠的基于胞元阵列的异面冲击分析有限元模型;基于简化的超折叠单元理论推导该蜂窝的准静态平台应力理论公式,理论值与仿真值相吻合验证理论公式的正确性。对不同壁厚边长比的蜂窝,在不同冲击速度下进行异面冲击仿真分析,利用LS-PrePost软件处理得到相应的接触力-位移曲线,进一步处理得到变形模式和平台应力,并以图表的形式加以展示与分析。结果 不同冲击速度下结构参数固定的蜂窝表现出LS、MS和HS等3种不同的异面冲击变形模式,从LS模式转变到MS模式再到HS模式的临界速度分别约为20 m/s和150 m/s;壁厚边长比对变形模式的影响可忽略。结论 该蜂窝动态平台应力随冲击速度(或壁厚边长比)的增加而增大,且增长速率不断提高。当其他参数固定时,LS模式和MS模式下该蜂窝的动态平台应力与冲击速度呈二次函数关系,HS模式下动态平台应力与冲击速度的平方呈线性关系;动态平台应力与壁厚边长比呈幂函数关系。基于仿真计算结果,得到了该蜂窝动态平台应力的经验表达式。     

Experimental study of the out-of-plane dynamic compression of hexagonal honeycombs

The out-of-plane crushing behaviour of four types of aluminium hexagonal honeycombs was extensively investigated over a wide range of strain rates where each test was conducted at a constant compressive velocity. The effects of specimen dimensions, relative density, strain rate and honeycomb cell size on the mechanical properties of honeycombs were studied. It was demonstrated that the mean plateau force was linearly related to the specimen dimensions. However, the calculated plateau stress varied with specimen dimensions and a minimum of 9 × 9 cells should be used in order to represent the bulk properties of honeycombs. A large strength enhancement of honeycombs was observed when the relative density and strain rate increased. The tangent modulus also increased towards the end of the crushing process, especially for those honeycombs with small values of wall thickness to edge length ratio (t/l). Semi-empirical relations were obtained to describe the effects of relative density (t/l ratio) and strain rate on the plateau stress. The difference in deformation patterns for honeycombs between quasi-static and dynamic loading conditions was also discussed.     

In-plane elastic constants and strengths of circular cell honeycombs

The in-plane elastic modulus, Poisson’s ratio, brittle crushing strength and plastic yielding strength of honeycombs with hexagonally packed circular cells are analyzed theoretically. The resulting theoretical expressions are compared with the numerical results obtained from a series of finite element analyses for circular cell honeycombs with various relative densities, leading to a good correlation. It is also found that the in-plane mechanical properties of circular cell honeycombs are significantly affected by the ratio of cell-wall thickness to cell radius. Though the elastic constants along the two principal directions of circular cell honeycombs are the same, the brittle crushing strength and plastic yielding strength along the two principal directions are not identical. Furthermore, the in-plane mechanical properties of circular cell honeycombs are compared to those of regular hexagonal honeycombs with straight and uniform-thickness cell walls to evaluate their microstructural efficiency.     

密度梯度蜂窝材料动力学性能研究

利用显式动力有限元方法数值研究了具有密度梯度六边形蜂窝材料的面内冲击动力学性能.根据功能梯度材料的概念,首先建立了具有密度梯度的蜂窝材料模型.基于此模型,具体讨论了密度梯度和冲击速度对六边形蜂窝材料变形模式和能量吸收性能的影响.研究结果表明,通过恰当地选择蜂窝材料的密度梯度,初始应力峰值明显减小,材料的能量吸收能力能够有效地得到控制.此结论为实现多胞材料动力学性能的多目标优化设计提供了新的设计思路.     

CRUSHING BEHAVIOUR OF ALUMINIUM HONEYCOMBS UNDER IMPACT LOADING

Understanding the crushing behaviour of honeycombs under dynamic loading is useful for crash simulations of vehicles and for design of impacting energy absorbers. Available experimental techniques, however, are not always able to provide satisfactory precision for tests on honeycombs under impact loading. This paper presents a new application of the Split Hopkinson Pressure Bar (SHPB) for testing honeycombs. Viscoelastic bars are used to improve the accuracy of measurements, and a generalised two-strain measurement method is applied to obtain a sufficient measurable maximum crush (up to 80%). Original experimental data (especially in the in-plane crushing directions) under impact loading are then reported. Differences between quasi-static and dynamic results are discussed.     

Elastic constants of 3-, 4- and 6-connected chiral and anti-chiral honeycombs subject to uniaxial in-plane loading

Finite element models are developed for the in-plane linear elastic constants of a family of honeycombs comprising arrays of cylinders connected by ligaments. Honeycombs having cylinders with 3, 4 and 6 ligaments attached to them are considered, with two possible configurations explored for each of the 3- (trichiral and anti-trichiral) and 4- (tetrachiral and anti-tetrachiral) connected systems. Honeycombs for each configuration have been manufactured using rapid prototyping and subsequently characterised for mechanical properties through in-plane uniaxial loading to verify the models. An interesting consequence of the family of ‘chiral’ honeycombs presented here is the ability to produce negative Poisson’s ratio (auxetic) response. The deformation mechanisms responsible for auxetic functionality in such honeycombs are discussed.     

Dynamic crushing of honeycombs and features of shock fronts

The in-plane dynamic crushing of 2D hexagonal-cell honeycombs has been simulated using finite elements to explore the dynamic response of cellular materials and to investigate the features of the crushing front and to examine the assumptions employed in a one-dimensional shock theory [Reid SR, Peng C. Dynamic uniaxial crushing of wood. Int J Impact Eng 1997;19:531–70; Tan PJ, Reid SR, Harrigan JJ, Zou Z, Li S. Dynamic compressive strength properties of aluminium foams. Part II – shock theory and comparison with experimental data and numerical models. J Mech Phys Solids 2005;53:2206–30]. It has been demonstrated that progressive cell crushing is observed to propagate through the material in a ‘shock’ like manner when the crushing velocity exceeds a critical value. The simulations show that there exists a zone at the shock front across which there are essentially discontinuities in the material ‘particle velocity’, ‘stress’ and ‘strain’ as defined herein. At supercritical crushing velocities the thickness of this zone remains about one cell size, which varies little with the crushing velocity and the relative density. Densification strain increases as crushing velocity increases and asymptotes to a limit once a shock front forms. It has also been shown that the one-dimensional shock theory [Reid SR, Peng C. Dynamic uniaxial crushing of wood. Int J Impact Eng 1997;19:531–70; Tan PJ, Reid SR, Harrigan JJ, Zou Z, Li S. Dynamic compressive strength properties of aluminium foams. Part II – shock theory and comparison with experimental data and numerical models. J Mech Phys Solids 2005;53:2206–30], which was based on an equivalent rigid-perfectly plastic-locking stress–strain curve, tends to overestimate slightly the crushing stress and energy absorbed.     

规则排列圆形蜂窝共面对角线方向缓冲性能的研究

目的 研究冲击速度和结构参数对规则排列圆形蜂窝共面对角线方向缓冲性能的影响规律。方法 使用有限元分析软件ANSYS/LS−DYNA建立规则排列圆形蜂窝共面对角线方向动态冲击有限元模型,基于此模型进行参数化仿真模拟,得到不同冲击速度和结构参数下规则排列圆形蜂窝共面对角线方向的变形模式、密实化应变、平台应力和能量吸收特征,并以图表的形式呈现。结果 在共面对角线方向的不同冲击速度下,规则排列圆形蜂窝表现出不同的变形模式。密实化应变在低速和高速冲击下,只与壁厚半径比有关;在中速冲击下,密实化应变同时受冲击速度和壁厚半径比的影响。在给定壁厚半径比下,共面平台应力(或最佳单位体积能量吸收)与冲击速度的平方呈线性关系;在给定冲击速度下,共面平台应力(或最佳单位体积能量吸收)与壁厚半径比呈幂指函数关系。结论 并基于有限元计算结果,得到了动态密实化应变、平台应力和单位体积能量吸收的经验表达式。     

多层规则排列圆形铝蜂窝共面缓冲优化

目的在不同速度的共面冲击载荷条件下,实现多层规则排列圆形铝蜂窝缓冲性能的优化。方法建立有限元分析模型以得到缓冲力学参数,并通过简化的能量吸收模型来评估其缓冲性能。结果多层规则排列圆形铝蜂窝缓冲性能与动态峰应力和动态密实化应变有关,是由冲击速度、变形模式和相关结构参数共同决定的。结论通过数值结果分析,得到模型变形的临界速度、动态密实化应变和动态峰应力的经验公式,并详细地介绍了可行的缓冲优化方法。     

EPE泡沫填充圆形纸蜂窝异面缓冲性能的试验研究

目的为了研究EPE泡沫填充对圆形纸蜂窝异面缓冲性能的影响,开展相关试验研究。方法对2种排列方式(规则/交错)以及不同填充形式(未填充、全填充、5种部分填充方式)的EPE泡沫填充圆形纸蜂窝结构,进行异面准静态和动态压缩试验,研究其异面变形模式和吸能特性,比较不同排列方式和泡沫填充对其异面缓冲性能的影响。结果静态压缩时,与未填充蜂窝结构相比,EPE填充使交错排列的平均平台应力和单位体积能量吸收分别增长了10.1%和8.9%,规则排列分别增长了7.1%和7.5%。结论 EPE填充使圆形纸蜂窝所承受的最大静应力增大,且交错排列时增长较明显;相同填充率下,填充方式对圆形纸蜂窝异面静态压缩的缓冲性能影响不大。动态压缩时,排列方式和泡沫填充仅对大载荷下圆形纸蜂窝的动态缓冲性能影响明显。EPE填充使圆形纸蜂窝异面缓冲性能得到改善,且交错排列方式优于规则排列。     

The in-plane linear elastic constants and out-of-plane bending of 3-coordinated ligament and cylinder-ligament honeycombs

Four novel cylinder-ligament honeycombs are described, where each cylinder has 3 tangentially-attached ligaments to form either a hexagonal or re-entrant hexagonal cellular network. The re-entrant cylinder-ligament honeycombs are reported for the first time. The in-plane linear elastic constants and out-of-plane bending response of these honeycombs are predicted using finite element (FE) modelling and comparison made with hexagonal and re-entrant hexagonal honeycombs without cylinders. A laser-crafted re-entrant cylinder-ligament honeycomb is manufactured and characterized to verify the FE model. The re-entrant honeycombs display negative Poisson’s ratios and synclastic curvature upon out-of-plane bending. The hexagonal and ‘trichiral’ honeycombs possess positive Poisson’s ratios and anticlastic curvature. The ‘anti-trichiral’ honeycomb (short ligament limit) displays negative Poisson’s ratios when loaded in the plane of the honeycomb, but positive Poisson’s ratio behaviour (anticlastic curvature) under out-of-plane bending. These responses are understood qualitatively through considering deformation occurs via direct ligament flexure and cylinder rotation-induced ligament flexure.     

蜂窝铝的面内动态冲击有限元研究

目的研究双壁厚蜂窝铝的面内动态冲击力学行为。方法利用Ansys/LS-DYNA有限元软件,建立双壁厚蜂窝铝有限元模型,分析蜂窝铝壁厚和冲击速度对蜂窝铝面内变形模式和平台应力的影响。结果随着冲击速度的增大,在蜂窝铝的压缩方向上观测到3种变形模式,获得了变形模式转换的临界速度,并给出了临界速度与厚跨比的关系式。计算了不同冲击速度和厚跨比下蜂窝铝的平台应力。结论变形模式对平台应力有很大的影响,不同的变形模式下呈现不同的规律:准静态模式时,平台应力与冲击速度无关;过渡模式和冲击模式时,平台应力随着冲击速度v的增大而增大,分别与v 1.5和v2成线性关系。根据有限元结果,拟合得到了不同的变形模式下平台应力与冲击速度的经验公式。     

Some theoretical considerations on the dynamic response of sandwich structures under impulsive loading

A theoretical solution is obtained to predict the dynamic response of peripherally clamped square metallic sandwich panels with either honeycomb core or aluminium foam core under blast loading. In the theoretical analysis, the deformation of sandwich structures is separated into three phases, corresponding to the transfer of impulse to the front face velocity, core crushing and overall structural bending/stretching, respectively. The cellular core is assumed to have a progressive crushing deformation mode in the out-of-plane direction, with a dynamically enhanced plateau stress (for honeycombs). The in-plane strength of the cellular core is assumed unaffected by the out-of-plane compression. By adopting an energy dissipation rate balance approach developed by earlier researchers for monolithic square plates, but incorporating a newly developed yield condition for the sandwich panels in terms of bending moment and membrane force, “upper” and “lower” bounds are obtained for the maximum permanent deflections and response time. Finally, comparative studies are carried out to investigate: (1) influence of the change in the in-plane strength of the core after the out-of-plane compression; (2) performances of a square monolith panel and a square sandwich panel with the same mass per unit area; and (3) analytical models of sandwich beams and circular and square sandwich plates.     

工字梁型蜂窝芯材共面冲击性能的有限元模拟

目的研究双壁厚工字梁型金属蜂窝芯材的共面冲击性能。方法借助有限元软件Ansys/LSDYNA,建立工字梁型蜂窝芯材的有限元模型,并进行CAE分析。结果在不同冲击速度下,工字梁型蜂窝芯材表现出不同的变形模式。当工字梁型金属蜂窝芯材的其他结构参数固定时,其共面动态峰应力与冲击速度的平方成线性关系;当冲击速度一定时,其共面动态峰应力与壁厚边长比成幂指数关系。同时,拟合得到了工字梁型金属蜂窝芯材共面动态峰应力关于壁厚边长比和冲击速度的经验计算公式。结论工字梁型蜂窝具有优良的结构和吸能能力,研究工字梁型蜂窝的冲击性能具有重要的科学研究和工程应用价值。     

Consistent multiscale analysis of heterogeneous thin plates with smoothed quadratic Hermite triangular elements

A consistent multiscale formulation is presented for the bending analysis of heterogeneous thin plate structures containing three dimensional reinforcements with in-plane periodicity. A multiscale asymptotic expansion of the displacement field is proposed to represent the in-plane periodicity, in which the microscopic and macroscopic thickness coordinates are set to be identical. This multiscale displacement expansion yields a local three dimensional unit cell problem and a global homogenized thin plate problem. The local unit cell problem is discretized with the tri-linear hexahedral elements to extract the homogenized material properties. The characteristic macroscopic deformation modes corresponding to the in-plane membrane deformations and out of plane bending deformations are discussed in detail. Thereafter the homogenized material properties are employed for the analysis of global homogenized thin plate with a smoothed quadratic Hermite triangular element formulation. The quadratic Hermite triangular element provides a complete C¹ approximation that is very desirable for thin plate modeling. Meanwhile, it corresponds to the constant strain triangle element and is able to reproduce a simple piecewise constant curvature field. Thus a unified numerical implementation for thin plate analysis can be conveniently realized using the triangular elements with discretization flexibility. The curvature smoothing operation is further introduced to improve the accuracy of the quadratic Hermite triangular element. The effectiveness of the proposed methodology is demonstrated through numerical examples.