Size effects in metal foam cores for sandwich structures
Size effects in metal foam cores for sandwich structures
复制标题
夹层结构金属泡沫芯材的尺寸效应
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
A. Waas
中科院分区：
文献类型：
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作者：
Joseph F. Rakow;A. Waas
测量了包括尺寸效应在内的泡沫铝的剪切响应，并对闭孔泡沫铝的剪切响应进行了量化。剪切刚度与密度呈线性关系，而强度与密度呈幂函数关系。在0.17/S的应变率范围内，材料的线性响应与应变率无关，而强度和能量吸收随应变率的增加而增加。基于复合材料圆柱体模型，解析地再现了刚度的密度依赖关系。在加载过程中，用光学技术测量了实验试件的应变场。通过对样品的同心子区域的评估，确定平均泡孔直径为18的样本大小是泡沫铝样品预测剪切模数的不确定度显著增加的维度。该长度尺度阈值被复制到具有随机分布缺陷的周期性有限元结构中。由于多种原因，金属泡沫塑料是三明治结构芯材的一种有吸引力的替代品。首先，利用金属泡沫芯，夹层结构的粘结剂基板可以通过生产中与金属表面薄板的整体粘合来消除，从而使夹层变硬并扩大其操作环境的范围。其次，泡沫金属表现出压缩应力-应变响应，这是吸收能量和缓解冲击的理想选择，具有长期、恒定的应力、塑性应变平台。1第三，开孔金属泡沫提供了一个机会，以消除水或低温气体渗透的灾难性性质，这些渗透已经使蜂窝夹层结构的长期使用陷入瘫痪。2第四，开放式结构还允许对夹层结构进行主动冷却，提高其可接受的工作温度范围。为了集成到夹层结构中，必须了解金属泡沫的剪切行为。目前文献中存在一些关于剪切行为的不同结果。一项研究发现，剪切强度和密度之间存在线性关系，3而立方格子模型在剪切载荷作用下预测了非线性的幂函数依赖关系。4另一项研究仅提供了几个关于泡沫铝熔体剪切刚度和强度的数据点。5此外，这些实验使用的是薄试件，没有考虑尺寸效应。本文给出了较宽密度范围内的全剪响应曲线。通过实验发现了刚度和强度的密度依赖关系，并对前者进行了解析再现。此外，还考虑了剪切响应的应变率相关性。用一种独特的涉及数字图像相关的方法对样品大小相对于平均细胞大小的影响进行了实验分析。用有限元模型再现了观察到的行为。这些分析确定了样本大小与细胞大小之比的阈值，低于该阈值的给定样本的剪切响应与显著的不确定性相关。
The shear response of aluminum foam, including size effects, is measured and quantified for a closed-cell aluminum foam. The shear stiffness is shown to depend linearly on density, whereas the strength exhibits a power law dependence. The linear response is shown to be independent of strain rate up to rates of 0.17/s, whereas the strength and energy absorption increase with increasing strain rate. The density dependence of the stiffness is reproduced analytically based on the composite cylinders model. Optical techniques are used to measure the strain field of the experimental specimens throughout the loading program. By evaluation of concentric subregions of the sample, a sample size of 18 mean cell diameters is determined to be the dimension below which the uncertainty in the predicted shear modulus of an aluminum foam sample increases significantly. This length scale threshold is replicated in a periodic finite element structure with randomly distributed imperfections. I. Introduction M ETAL foams represent an attractive alternative for sandwich structure cores for multiple reasons. First, with metal foam cores, the adhesive substrate of a sandwich structure may be eliminated with in-production integral bonding to metallic face sheets, stiffening the sandwich and broadening its range of operating environments. Second, metal foams exhibit a compressive stress‐strain response that is ideal for energy absorption and impact alleviation with a long, constant stress, plastic strain plateau. 1 Third, an opencell metal foam offers an opportunity to eliminate the catastrophic nature of water or cryogenic gas permeation that has crippled the long-term use of sandwich constructions with honeycomb cores. 2 Fourth, an open-cell construction also allows for active cooling of the sandwich structure, elevating its range of acceptable operating temperatures. For integration into sandwich structures, the shear behavior of metal foam must be understood. Some disparate results regarding shear behavior currently exist in the literature. One study found a linear relationship between shear strength and density, 3 whereas a cubic lattice model subjected to shear loading predicted a nonlinear power law dependence. 4 Another investigation offers only a few data points for shear stiffness and strength of melt-foamed aluminum. 5 Furthermore, these experiments involved thin specimens, with no account for size effects. The present paper offers the full shear response curves for a broad range of density. The density dependence of stiffness and strength are found experimentally with the former being reproduced analytically. The strain rate dependence of the shear response is also considered. The effect of specimen size, relative to the mean cell size, is analyzed experimentally with a unique approach involving digital image correlation. The observed behavior is reproduced with a finite element model. These analyses identify a threshold in the ratio of specimen size to cell size, below which the shear response of a given sample is associated with a significant amount of uncertainty.