Compressive response of circular cell polycarbonate honeycombs under inplane biaxial static and dynamic loading. Part I: experiments

The crushing response of a polycarbonate circular cell honeycomb to inplane biaxial loading is analyzed. The study involves a combination of static and dynamic experiments. Static experiments corresponding to several different biaxial loading conditions under displacement control are carried out in two different inplane directions respectively. Dynamic experiments related to various impact forces under inplane biaxial loading in two different mutually orthogonal directions, respectively, are conducted. In the first phase of the response, the material deforms in a uniform fashion. Next, a nonlinear phase caused by the progressive localization of deformation is observed. This phase is characterized by the variation of overall (macroscopic) stiffness. The progressive localization causes the walls of each cell within the localized region to contact each other. These periodic honeycomb materials show different collapsed modes under different biaxial loading histories. Experimental measurements indicate how the magnitude of the collapse load varies and how the stress–strain response changes as a function of load biaxiality. The experimental crushing responses between static and dynamic cases are compared.     

Elastic stability of skew laminated composite plates subjected to biaxial follower forces

The present study investigates the elastic stability of skew laminated composite plates subjected to biaxial inplane follower forces by the finite element method. The plate is assumed to follow first-order shear deformation plate theory (FSDPT). The kinetic and strain energies of skew laminated composite plate and the work done by the biaxial inplane follower forces are derived by using tensor theory. Then, by Hamilton's principle, the dynamic mathematical model to describe the free vibration of this problem is formed. The finite element method and the isoparametric element are utilized to discretize the continuous system and to obtain the characteristic equations of the present problem. Finally, natural vibration frequencies, buckling loads (also the instability types) and their corresponding mode shapes are found by solving the characteristic equations. Numerical results are presented to demonstrate the effects of those parameters, such as various inplane force combinations, skew angle and lamination scheme, on the elastic stability of skew laminated composite plates subjected to biaxial inplane follower forces.     

The inplane elastic properties of circular cell and elliptical cell honeycombs

Summary The inplane elastic properties of perfectly circular and elliptic cell honeycombs are derived through an analytical method and validated numerically. In the case of perfectly circular cell hexagonally packed honeycomb, the inplane elastic properties are shown to be isotropic. However, a departure from circularity of the cells leading to cell ellipticity results in the inplane properties becoming orthotropic. The orthotropic elastic constants are also derived analytically and validated numerically.     

铝塑复合包装材料废弃物分选技术

目的 针对铝塑复合包装材料废弃物分离不够彻底,导致产品纯度不高、分离效率低、分离工艺不够完善等问题,采用绿色环保的铝塑活性介质进行铝塑分选技术研究,优化分离工艺参数.方法 选择天然固体酸柠檬酸溶液作为铝塑复合废料分选的分离溶剂,研究柠檬酸浓度、反应温度、液固比、搅拌速度和裁切尺寸等因素对铝塑复合材料分离效果的影响.并根据正交试验和极差分析优化出分离时间短、铝损失率较低的分离工艺.结果 在柠檬酸浓度为2 mol/L,温度为100℃,液固比为400 L/kg,搅拌速度为650 r/min,裁切尺寸为0.5 cm×0.5 cm的条件下,铝塑分离率达到100％,分离时间为65 min,铝的质量损失率为0.66％.结论 柠檬酸作为一种新型天然分离剂,对铝的腐蚀率低,此技术为铝塑复合材料废弃物回收再利用工业化生产提供了参考.     

Strain localization in circular honeycombs under in-plane biaxial quasi-static and low-velocity impact loading

Strain localization in a finite block of circular honeycomb is studied using a phenomenological approach based on the structural response of the honeycombs. The deformation modes characteristic for a circular honeycomb material under in-plane biaxial compression are identified from the experiments and described analytically for compression strains up to about 15%. It is concluded that the particular deformation modes depend on the local strain field, and modes with different dominant strains can co-exist inside a finite block subjected to equi-biaxial remote strains. The relationships between the local strain components for the development of these modes are determined. Using the proposed approach to the strain localization, it is shown that for equal remote strains applied to a finite block of honeycombs, larger remote stresses would occur when assuming homogeneous deformation inside the block in comparison to the calculated stress when the strain inhomogeneity takes place. A comparison between the theoretical and experimental results is made for a finite honeycomb block under quasi-static equi-biaxial compression.     

Evaluation of the Micropolar elasticity constants for honeycombs

Summary The Micropolar and Lamè constants for a circular cell polycarbonate honeycomb are calculated using a finite element representation of the honeycomb microstructure. A hexagonally packed, circular cell, honeycomb sheet with a rigid circular inclusion was numerically analyzed under uniaxial tension. Micropolar Elasticity was found to be the best continuum representation of the discrete honeycomb. This conclusion was arrived at by matching the strain field in the discrete honeycomb with that predicted by a micropolar elastic continuum representation of the honeycomb. The minimum ratio of inclusion radius a to cell diameter d, for the honeycomb to be approximated accurately as a continuum was between 16 and 20. A radius of 20d and 32d showed a near perfect approximation to a continuum.     

Numerical experiments on the determination of stress concentration factors

A brief discussion of relevant applications of the finite element method is presented, and two cases of relatively high stress concentration are considered. For a slot with semi–circular ends in a plate subjected to uniaxial stress, the stress concentration factors obtained numerically, by use of the finite element method, are compared with corresponding experimental results. The case of a corrugated hole in a plate under 1:1 biaxial stress is also examined, and stress concentration factors determined using the finite element approach are compared with exact values obtained by application of Muskhelishvili's method.     

CFRP圆形胞元蜂窝芯层面外剪切模量

为了减少卫星的热变形,将碳纤维增强树脂基复合材料（CFRP）材料圆管周期排布获得新型圆形胞元蜂窝芯层。考虑无论是Ressiner理论还是商业有限元软件ABAQUS,层合板计算热变形时,芯层的面外剪切模量均很重要,因此对CFRP圆形胞元蜂窝芯层的面外剪切进行了研究。分别从应力与应变的角度基于能量等效原理求出圆形胞元蜂窝芯层的面外剪切模量公式。以T300/环氧材料的工程常见铺层为例,比较基于ABAQUS软件计算所得剪切模量仿真解与公式计算所得理论解,其最大误差仅为10.4%,证实公式对于CFRP材料的适用性。同时用（±45°）₂铺层的T300/环氧芯层完成双剪试验,试验结果与理论结果误差为24.1%,与前人研究的铝蜂窝面外剪切模量理论解与试验解的误差相近。最后通过仿真手段证实,24.1%的误差对整体夹层结构影响较小,说明公式具有良好的工程应用价值。为以后CFRP圆形胞元蜂窝芯层的设计提供重要基础。     

蜂窝纸板振动传递特性的有限元仿真分析

目的针对蜂窝纸板的振动防护性能,研究不同结构和材料参数的蜂窝纸板振动传递特性的有限元仿真分析方法。方法利用有限元软件Abaqus/Standard建立蜂窝纸板-质量系统模型,设定2种蜂窝纸板,分别具有不同的面纸材料参数和蜂窝胞元边长。仿真分析蜂窝纸板的振动传递特性,并对其进行实验验证。结果通过仿真和实验得到了蜂窝纸板的振动传递率-频率曲线,共振频率的仿真结果与实验值误差小于3.43%,共振时振动传递率的仿真结果与实验值误差小于11.31%。结论利用该有限元仿真方法,能够获得不同结构和材料参数的蜂窝纸板的振动传递特性。仿真分析结果表明,面纸定量对蜂窝纸板振动传递特性的影响不大,而蜂窝胞元边长较大的蜂窝纸板,其系统共振频率较小,振动传递率变化不明显。     

正多边形外接填充圆形蜂窝异面动态缓冲性能

目的 为了研究正多边形外接填充圆形蜂窝的缓冲性能,建立不同正多边形外接填充圆形蜂窝的冲击有限元模型,分析研究多边形填充对圆形蜂窝缓冲性能的影响.方法利用Ansys/LS-DYNA建立正三、四、五、六边形外接填充圆形蜂窝的有限元分析模型,用六水平等级法评价分析各有限元模型在异面方向不同冲击速度下的力学性能、变形模式和能量吸收特性.结果正多边形与圆形蜂窝产生了较强的耦合响应,使组合结构的接触载荷和总能量吸收值均大于两者单独冲击数值之和;正六边形外接填充圆形蜂窝结构的六水平等级评价均为A,优于其他组合类型,且在不同冲击速度下不同正多边形外接填充圆形蜂窝的评价结果大致相同;正六边形外接蜂窝结构在冲击载荷下存在3种变形模式,随冲击速度的变化而变化,蜂窝壁厚对其的影响较小.随着冲击速度和壁厚的增大,动态峰应力、密实化总能量吸收和比吸能均有一定程度的提升.结论在耦合效应和动态冲击载荷的综合作用下,正六边形外接填充圆形蜂窝结构的动态力学性能较其他3种结构更为优异;随着蜂窝壁厚和冲击速度的增加,正多边形外接填充圆形蜂窝结构的承载能力和吸能能力都得到增强.     

结构参数对CFRP蒙皮-铝蜂窝夹层板低速冲击性能的影响

针对碳纤维增强树脂复合材料（CFRP）蒙皮-铝蜂窝夹层结构,使用半球头式落锤冲击试验平台进行了低速冲击载荷下蜂窝芯单元尺寸对夹层板冲击性能影响的试验探究,并基于渐进损伤模型、内聚力模型和三维Hashin失效准则,在有限元仿真软件ABAQUS中建立了含蒙皮、蜂窝芯、胶层的CFRP蒙皮-铝蜂窝夹层板精细化低速冲击仿真模型,仿真结果与试验结果吻合较好。利用该数值模型进一步探究了蜂窝芯高度、蒙皮厚度和蜂窝芯壁厚等结构参数对于蜂窝夹层板低速冲击吸能效果的影响。结果表明:增大铝蜂窝芯的单元边长,会减小蜂窝夹层板的刚度,提升夹层板的吸能效果;芯层高度对夹层板的刚度及抗低速冲击性能影响较小;增大蜂窝夹层板的蒙皮厚度,可以提高夹层板的刚度,但会降低夹层板的吸能效果;增大蜂窝芯的壁厚,可以提高夹层板的刚度和抗低速冲击性能。      

Mechanical Properties of a Novel Zero Poisson's Ratio Honeycomb

In this paper, a novel honeycomb is proposed by embedding a rib into every cell of the existing zero Poisson's ratio (ZPR) configuration, semi re‐entrant honeycomb (SRH). Analytical model is developed to investigate the in‐plane mechanical properties of the new honeycomb, and the resulting theoretical expressions are compared with the experimental tests and numerical results obtained from two different finite element (FE) models (3D beam model and 3D solid model), leading to a good correlation. FE analysis, analytical modeling, and experimental tests of the new honeycomb show that it can achieve ZPR effect in two principal directions. For further studies, parameters analyses are carried out to explore the dependence of the in‐plane mechanical properties versus the geometric parameters. The results show that bending is the dominated deformation model when the new honeycomb is compressed along the x‐ direction, while stretch controlled in the y‐ directional compression. It is remarkable that the new proposed honeycomb features superior specific stiffness and more flexible in mechanical properties tailoring compared to the other ZPR honeycombs in the literature. Given these benefits, the new honeycomb may be promising in some practical applications.

     

基于特征单元的三角形蜂窝异面压缩的有限元分析

目的 研究三角形蜂窝排列方式对三角形蜂窝异面动态压缩性能的影响。方法 借助Ansys/LS-DYNA建立基于特征单元的三角形蜂窝异面动态压缩的有限元分析模型,研究三角形蜂窝排列方式对三角形蜂窝异面压缩性能的影响。结果 将三角形蜂窝胞元阵列模型的有限元分析结果与理论值进行对比,证明三角形蜂窝的有限元模型是可靠的,随后将三角形胞元阵列模型与此研究中采用的特征单元模型计算结果进行对比,结果显示2种有限元计算模型的计算结果一致,证明此研究特征单元结构的选取和模型的建立是可靠的。结论 不同排列方式对三角形蜂窝在异面方向上的动态峰应力和单位体积能量吸收没有影响。     

双轴受压状态下的高延性纤维增强水泥基复合材料本构模型

基于Darwin和Pecknold考虑混凝土双轴力学行为的方法,建立一个同时考虑双轴受压状态下非线性力学行为和抗压强度变化的高延性纤维增强水泥基复合材料(ECC)二维正交各向异性本构模型。在因双轴加载而产生的正交各向异性的2个方向上引入等效单轴应变,建立非线性应力-等效单轴应变关系以考虑ECC的双轴非线性行为,并采用一条双轴强度包络线确定2个方向上的抗压强度。推导模型的显式数值算法,编写包含该算法的用户自定义材料子程序UMAT,并嵌于有限元计算程序ABAQUS v6.14中。通过对两组不同配合比的ECC试件在不同应力比下的双轴受压加载试验进行数值分析验证本模型的有效性。数值计算得到的主压应力方向上的应力-应变曲线及预测的抗压强度与试验结果吻合较好,表明该文提出的本构模型能够有效地预测ECC在双轴受压状态下的非线性力学行为和破坏强度。     

Transverse elastic shear of auxetic multi re-entrant honeycombs

The paper describes the transverse shear properties of a novel centresymmetric honeycomb structure evaluated using analytical and finite element models. The cellular structure features a representative volume element (RVE) geometry allowing in-plane auxetic (negative Poisson’s ratio) deformations, and multiple topologies to design the honeycomb for multifunctional applications. The out-of-plane properties are calculated using a theoretical approach based on Voigt and Reuss bounds. The analytical models are validated using a full scale Finite Element technique to simulate transverse shear tests, a quarter FE of the RVE with periodic shear conditions and an FE homogenisation method for periodic structures. The comparison between the analytical and numerical models shows good convergence between the different set of results, and highlights the specific deformation mechanism of the multi re-entrant honeycomb cell.     

Theoretical prediction and numerical simulation of honeycomb structures with various cell specifications under axial loading

The axial crushing of honeycomb structures with various cell specifications is studied analytically and numerically. Based on the Super Folding Element theory, a new method for predicting the mean crushing stress of honeycomb structures with various cell specifications under axial loading is developed. In this new theoretical method, two types of simplified folding modes named SFM1 and SFM2 are proposed. The mean crushing stress and the folding wavelength for honeycomb structures with various cell specifications are then determined by a minimum principle. The effective crushing distance and the loading rate effect are both considered. In order to illustrate the effectiveness of the proposed approach, numerical simulations are carried out by employing the explicit finite element code LS-DYNA. The bond of the honeycomb panels is simulated by using a tie-break contact. It can be seen that the analytical solutions are in agreement with the numerical results as well as the Wizerbicki’s solutions.     

圆形蜂窝共面冲击力学性能

目的基于有限元模拟的方法,比较研究规则和交错排列的圆形蜂窝共面动态冲击力学性能。方法利用Ansys/LS-DYNA建立2种蜂窝的共面冲击分析有限元模型。结果借助于该模拟方法,分析得到在结构参数一致,冲击速度不同的情况下,规则排列的圆形蜂窝变形模式呈现3个阶段,即"X","V"和"一"字形,交错圆形蜂窝变形模式几乎相同,呈"一"字形。得出了2种排列方式的圆形蜂窝的变形模式转换速度与壁厚半径比的关系。根据有限元模拟结果,推导出了动态峰应力关于结构参数和冲击速度的经验公式。结论用有限元模拟的方法得到了2种排列方式的圆形蜂窝的共面冲击力学性能,为圆形蜂窝芯材的优化设计提供了参考依据。     

六边形蜂窝芯异面类静态压缩力学行为的仿真分析

目的研究六边形蜂窝芯材异面类静态压缩载荷的数值模拟方法及相关力学行为。方法基于蜂窝单元阵列的方法,构筑了单双壁厚六边形蜂窝芯材异面类静态压缩有限元数值计算模型和分析方法。结果借助于该模拟方法,分析计算了不同结构参数条件下单双壁厚六边形蜂窝芯材的异面变形模式、变形曲线和类静态峰应力值,并绘制了相应的图、压缩力位移曲线和数据表格。结论将计算结果与现有的实验和理论计算结果作对比分析可知,计算结果与已有结果吻合较好,证明了所提出的有限元分析方法的可靠性。     

基于响应面全局优化技术的蜂窝板材料性能参数修正

蜂窝夹层板结构广泛应用于航空航天行业中,建立准确的蜂窝夹芯板有限元模型是分析和优化航天器微振动的必要前提。基于蜂窝芯的力学等效参数模型,建立了蜂窝板的动力学有限元模型。使用正交数值实验设计筛选出对蜂窝板动力学性能影响最大的蜂窝芯等效材料参数,并利用基于响应面模型自适应采样技术的全局优化方法快速地完成了蜂窝芯关键材料参数的优化修正。修正后的蜂窝板有限元模型前六阶模态频率与实验结果的平均误差小于1%。     

Experimental and numerical analysis of flexural and impact behaviour of glass/pp sandwich panel for automotive structural applications

Cost and recyclability are among the primary factors on exploiting the engineering materials for their new applications. In this context, glass/pp-based sandwich panel has been studied experimentally and numerically with the aims of its potential applications in the automotive structures. The first part of this work presents the experimental results achieved for the load-carrying capacity of panels using three-point bend tests for its static flexural behaviour. Static behaviour is studied to compare the top-roller diameter effect on the flexural behaviour of the panels and shows a significant difference in the results. Impact behaviour of the panels is explored using three different types of impactor end-shapes that generate different levels of damage in the material with the same level of impact energy. The second part of this paper deals with the development of numerical models for the three-point bend and impact behaviour of the panels using a commercial finite element code of Abaqus. Strain energy-based homogenisation technique is employed to determine the equivalent orthotropic properties of complex circular honeycomb core material. The finite element models predict to a good level of the static and impact behaviour of the material when compared with the experiments.