低密度开孔泡沫蠕变松弛特性分析

利用三维Voronoi模型和有限元方法分析了胞壁材料具有粘弹特性的低密度开孔泡沫的蠕变和应力松弛行为.采用了三参量标准线性固体模型来描述胞壁材料的粘弹特性.所得结果表明.低密度开孔泡沫具有与其胞壁材料相同的松弛时间,当相对密度较低时(低于1%)开孔泡沫的松弛模量与胞壁材料的松弛模量和泡沫相对密度平方成正比.此外,计算结果还表明,低密度开孔泡沫在较小的初始应力条件下具有与其胞壁材料相同的延迟时间.其蠕变柔度与胞壁材料的蠕变柔度和泡沫相对密度平方倒数基本成正比.但随着初始应力值的增大,泡沫的延迟时间将会显著增加.     

Kelvin结构开孔泡沫材料的弹性性能研究

采用一修正的十四面体结构模型(Kelvin结构模型)对开孔泡沫金属的弹性性能进行研究,对低密度开孔泡沫材料表现出不可压的特性进行了分析。该模型考虑作用在泡沫筋条上的弯矩、剪力和轴向力,以及轴向力的平衡。修正模型的数值计算结果与实验结果及其他模型的结果进行了对比,结果表明修正模型计算的杨氏模量比原有模型的略有提高,筋条截面为星形的修正模型计算的结果与实验比较符合。在密度等同的条件下,筋条截面惯性矩越大的开孔泡沫材料,其弹性模量也越大,而泊松比则越小。Kelvin结构的开孔泡沫材料的泊松比随相对密度的减小而趋于0.5。     

球形孔洞泡沫铝力学行为的SPH分析

分别基于体心立方元胞模型和随机孔洞模型建立了泡沫铝SPH模型.采用SPH方法分析了准静态加载条件下泡沫铝的单轴压缩力学性能.最大应变达70%.SPH计算所得应力-应变曲线表现出明显的弹性、平台和压实三段.分析了泡沫铝的微观变形机理,结果表明规则模型和随机模型均呈现出明显的局部塑性变形带,其中随机泡孔模型的孔壁变形以弯曲为主,局部塑性变形带表现更为明显.本文研究结果同时还说明了采用SPH方法研究泡沫材料力学行为的可行性与适应性.     

基于三维细观力学模型的开孔泡沫弹性性能预测

泡沫材料的宏观力学性能主要取决于基体材料的力学特性及其微细观结构特征,基于细观力学模型的分析方法是泡沫材料力学性能研究的重要途径.文中构建了描述中等孔隙率开孔弹性泡沫材料微结构特征的三维随机分布球形泡孔模型,并采用有限元方法对弹性泡沫压缩变形进行了模拟,并计算给出了不同孔隙率弹性泡沫材料弹性模量、剪切模量、体积模量以及泊松比的分布,建立了相应的唯象表达式.研究表明,泡孔分布的随机性导致泡沫材料微结构刚度分布不均匀,泡沫压缩变形过程中不断发生局部泡孔坍塌现象直至密实,使得泡沫材料的宏观压缩应力应变曲线没有明显的平台段.泡沫材料弹性参数唯象模型的研究显示,该模型预测结果与理论模型一致,且与测试结果吻合,论文建立的唯象表达式能够很好地预测泡沫材料的弹性力学性能.     

闭孔泡沫铝材料十四面体模型的改进

基于对闭孔泡沫铝发泡过程更为合理的假设,提出了描述胞体结构的改进的十四面体模型,使之可以反映密度增大时质量集中于支柱和顶点的情况。采用有限元方法及耦合边界条件,研究了闭孔泡沫铝的相对弹性模量、泊松比等弹性特征与胞体参数的关系,给出了拟合的弹性模量的计算公式,并对模型在弹性压缩变形下应力分布进行了分析。通过与已有模型的比较表明,改进模型可以较好地模拟闭孔泡沫铝材料的弹性性能。     

泡沫铝的单向力学行为

本文对不同孔径的开孔泡沫铝材料的单向拉伸性能和单向压缩性能进行了研究,揭示了泡沫铝材料的变形机理,并且发现相对密度不是确定材料力学属性的唯一参数,孔径大小对材料的力学性能也有一定的影响。基于实验数据,我们讨论了材料的宏观力学性能和微观结构的联系,并利用Ramberg-Osgood模型描述了材料的单轴拉伸一维应力应变关系。     

基于十四面体模型的闭孔泡沫材料动态力学性能的有限元分析

应用有限元方法分析了基于十四面体模型的三维闭孔泡沫材料的动态力学性能。计算中所有十四面体具有相同的尺寸，主要研究了不同初始冲击速度、不同相对密度以及组成泡沫的机体材料的应变强化对泡沫材料的变形模态、平台力及密实化应变能的影响，尽可能全面地描述了泡沫材料的能量吸收特性。数值结果表明:冲击速度对泡沫模型的模态影响较大,特别受到高速冲击时，冲击端泡沫形成I形然后向支撑端传播；相对密度对能量吸收能力的贡献较大，密实化应变能随相对密度呈二次曲线变化；冲击速度、相对密度及机体材料的应变强化分别与坪应力呈线性关系。     

多胞材料的力学行为

多胞材料具有独特的力学性质,其工程应用日益增加.人造多胞材料可以分为蜂窝材料和泡沫材料两类.本文介绍了这两类材料在不同载荷条件下力学行为的研究概况.对于某些天然材料(木材和松质骨)的多胞结构及其模型也作了简要介绍.     

多胞材料的力学行为

多胞材料具有独特的力学性质,其工程应用日益增加.人造多胞材料可以分为蜂窝材料和泡沫材料两类.本文介绍了这两类材料在不同载荷条件下力学行为的研究概况.对于某些天然材料(木材和松质骨)的多胞结构及其模型也作了简要介绍.     

在材料研制中的连续介质细观力学有限元建模现状评论（译文）

评述了机械载荷下材料力学行为有限元模拟的先进技术.分析 了考虑材料微观及细观结构情况下，对材料变形、损伤、断裂进行模 拟时各种方法的优缺点及发展前景.阐述了对材料行为模拟方法的发 展，包括基本的及先进的方法，如体胞方法、真实结构模拟、粘结区 模型等.分析了在先进新材料的开发中运用有限元方法的可能性     

复合泡沫塑料力学行为的研究综述

复合泡沫塑料是一种重要的防护材料,它在国防工业和民用工业各部门均有许多重 要的应用,对这类材料的力学行为进行研究具有重要的学术价值和应用前景. 本文对复合泡沫塑料力学行为的研究文献进行了综述.首先,对复合泡沫 塑料力学行为研究的早期工作进行了简介.然后,重点介绍了复合泡沫塑料力学行为 研究的最新进展,其中也包括作者近期在该领域开展的一些工作;对 复合泡沫塑料进行了静、动态压缩实验和细观加载实验,研究了材料的宏观变形规 律和细观失效机制;在理论研究方面,探讨了复合泡沫塑料的能量吸收和缓冲特性, 从宏、细观力学分析出发研究了复合泡沫塑料有关力学性能的理论预测问题;还利 用计算机和通用软件对高密度复合泡沫塑料进行了有限元分析,研究了高密度复合 泡沫塑料的失效行为.最后,给出对该领域研究工作的一些展望.     

宽γ辐照剂量范围内硅泡沫本构模型研究

基于实验和理论建模研究了白炭黑增强硅泡沫材料在γ辐照剂量范围为0~1000kGy作用后的单轴压缩力学行为。实验结果表明辐照导致硅泡沫出现明显硬化现象,初始杨氏模量和固定应变下应力幅值均随γ辐照剂量近似线性增加。辐照后硅泡沫泡孔结构完整,硅橡胶基体中高分子交联反应占主导,且交联密度随辐照剂量线性增大。基于实验分析结果,实现了Ogden Hyperfoam超弹本构模型参数与辐照剂量的关联。结果表明初始剪切模量参数与辐照剂量成线性关系,硬化指数和泊松比参数与辐照剂量无关。基于应力应变实验数据拟合得到模型参数,并与未参与拟合的实验数据对比,验证了模型的准确性,表明该模型能够表征宽辐照剂量范围内硅泡沫的压缩力学行为。     

宽γ辐照剂量范围内硅泡沫本构模型研究

基于实验和理论建模研究了白炭黑增强硅泡沫材料在γ辐照剂量范围为0~1000kGy作用后的单轴压缩力学行为。实验结果表明辐照导致硅泡沫出现明显硬化现象，初始杨氏模量和固定应变下应力幅值均随γ辐照剂量近似线性增加。辐照后硅泡沫泡孔结构完整，硅橡胶基体中高分子交联反应占主导，且交联密度随辐照剂量线性增大。基于实验分析结果，实现了Ogden Hyperfoam超弹本构模型参数与辐照剂量的关联。结果表明初始剪切模量参数与辐照剂量成线性关系，硬化指数和泊松比参数与辐照剂量无关。基于应力应变实验数据拟合得到模型参数，并与未参与拟合的实验数据对比，验证了模型的准确性，表明该模型能够表征宽辐照剂量范围内硅泡沫的压缩力学行为。     

内部填充泡沫铝的柱壳力学响应数值模拟

针对泡沫铝及其填充圆柱壳的变形模式复杂、理论分析困难的问题,在分析泡沫金属唯象本构模型的基础上,用Bilkhu/Dubois可压缩泡沫模型描述泡沫铝的力学行为,用随机几何缺陷描述结构的可能缺陷形式,采用有限元法对内部填充泡沫铝的圆柱壳结构在轴向载荷作用下的静、动态力学响应进行了数值模拟.数值模拟结果与实验结果较一致,表...     

玻璃纤维增强聚氨酯泡沫塑料的压缩力学性能研究

本文研究了两种不同密度的玻璃纤维增强聚氨酯泡沫塑料在准静态压缩下的力学性能。给出了与相应密度的普通泡沫塑料力学性能的比较，实验结果表明：两种增强泡沫塑料在压缩载荷作用下，具有不同于普通泡沫塑料的应力－应变特性，压缩模量和强度一般均有不同程度的提高，而且对相同纤维含量的增强泡沫塑料来说，密度较高的材料增强效果较好。     

Mechanical characterization of the role of defects in sintered FeCrAlY foams

Open celled metal foams fabricated through metal sintering are a new class of material that offers novel mechanical and acoustic properties. Previously, polymer foams have been widely used as a means of absorbing acoustic energy. However, the structural applications of these foams are limited. The metal sintering approach offers a cost- effective means for the mass-production of open-cell foams from a range of materials, including high-temperature steel alloys. In this first part of two-paper series, the mechanical properties of open-celled steel alloy (FeCrAlY) foams were characterized under uniaxial compression and shear loading. Compared to predictions from established models, a significant knockdown in material properties was observed. This knockdown was attributed to the presence of defects throughout the microstructure that result from the unique fabrication process. Further in situ tests were carried out in a SEM (scanning electronic microscope) in order to investigate the effects of defects on the properties of the foams. Typically, the onset of plastic yielding was observed to occur at defect locations within the microstructure. At lower relative densities, ligament bending dominates, with the deformation initializing at defects. At higher relative densities, an additional deformation mechanism associated with membrane elements was observed. In the follow-up of this paper, a finite element model will be constructed to quantify the effects of defects on the mechanical performance of the open-cell foam. The project supported by the US Office of Naval Research (N000140210117), the National Basic Research Program of China (2006CB601202), the National Natural Science Foundation of China (10328203, 10572111, 10632060), and the National 111 Project of China (B06024).     

泡沫铝率相关本构模型及其在三明治夹芯板冲击吸能特性的应用研究

高孔隙率泡沫铝芯体三明治板具有轻质、高比刚度和减振吸能等优良的力学特性和物理特性,被广泛地应用于碰撞吸能部件上.近年来,高孔隙率泡沫铝在动态压缩下是否具有应变率敏感性成为广大学者的研究焦点.论文建立了横观各向同性率相关本构模型来描述高孔隙率泡沫铝的应变率效应,给出了有限元的计算步骤,基于ABAQUS/Explicit平...     

Microstructure and Tensile Mechanical Properties of Anisotropic Rigid Polyurethane Foam

An understanding of the mechanical properties of solid foams facilitates effective use of such materials, which are often deployed in load-bearing applications such as impact absorbers, cushioning and sandwich structures. This study is an experimental investigation that focuses on the deformation response of rigid polyurethane foam to tension. Microstructural features such as the size and geometry of constituent cells and the struts that define the cell edges, as well as their stiffness and tensile strength, are examined. The nature of cell deformation and fracture are identified through microscopy and the associated micromechanics analyzed. Results show that the cells are elongated and thus the foam exhibits anisotropic properties. Flexure of the struts that define the cell edges is the primary mechanism governing deformation and failure. Information on the mechanical, microstructural and deformation characteristics elicited through this investigation will facilitate formulation of idealized cell-based models to account for the mechanical response of rigid polymeric foams.     

Analytical models for the mechanical behavior of closed and open-cell Al foams

Two 3D analytical models are proposed for the determination of mechanical properties of Al closed and open-cell foams under compression load. The first model, referring to closed cell foams, is symmetrical, considering ellipsoid cells equally arranged in a rectangular plate, whereas the second one, related to open-cell foams, consists of a simple unit parallelepiped cell.The closed cell model produces much higher values of the plateau stress than comparable experimental results, mainly due to the associated conditions of symmetry, contrary to the open-cell model which yields values close to experimental and theoretical results of other investigators. Additionally, in the latter case, a unit cubic cell is also considered for comparison reasons. Both models are solved by the finite element method using a commercial program. The open-cell model is simple, time sparing and easy to use. Finally, a fracture analysis of the model is conducted based on the energy density concept and results are given for distortion and dilatational effects.     

On the microstructure of open-cell foams and its effect on elastic properties

Synthetic open-cell foams have a complex microstructure consisting of an interconnected network of cells resulting from the foaming process. The cells are irregular polyhedra with anywhere from 9 to 17 faces in nearly monodisperse foams. The material is concentrated in the nearly straight ligaments and in the nodes where they intersect. The mechanical properties of such foams are governed by their microstructure and by the properties of the base material. In this study micro-computed X-ray tomography is used to develop 3D images of the morphology of polyester urethane and Duocel aluminum foams with different average cell sizes. The images are used to establish statistically the cell size and ligament length distributions, material distributions along the ligaments, the geometry of the nodes and cell anisotropy. The measurements are then used to build finite element foam models of increasing complexity that are used to estimate the elastic moduli. In the most idealized model the microstructure is represented as a regular Kelvin cell. The most realistic models are based on Surface Evolver simulations of random soap froth with N³ cells in spatially periodic domains. In all models the cells are elongated in one direction, the ligaments are straight but have a nonuniform cross sectional area distribution and are modeled as shear deformable beams. With this input both the Kelvin cell models and the larger random foam models are shown to predict the elastic moduli with good accuracy but the random foams are 5–10% stiffer.