The influence of strain-induced damage on the mechanical response of open-cell aluminum foam

Amsterdam, Emiel; Vries, J. H. B. de; Hosson, J.Th.M. De; Onck, Patrick

doi:10.1016/j.actamat.2007.10.034

Cited by 54 publications

(35 citation statements)

References 12 publications

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“…The yield stress ratio obtained in compression is 1.56 Ref. [13,16] for both heat treatments. The measured aspect ratio of the cell shape is 1.43 ± 0.15.…”

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The Influence of Cell Shape Anisotropy on the Tensile Behavior of Open Cell Aluminum Foam

et al. 2008

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There are numerous processes for the fabrication of openand closed cell metal foams and some of these methods result in a strong anisotropy in cell shape. The mechanical properties of these specific foams, such as the stiffness, yield stress and ultimate tensile strength (UTS) (see Fig. 1), also show anisotropy which is often linked to the cell shape. [1,2,3,4,5] Gibson and Ashby (G&A) constructed an analytical beam bending model to calculate the influence of the cell aspect ratio, i.e. the long cell axis divided by the short cell axis, on the stiffness and plastic strength. [6] Descriptions based on continuum approaches have been proposed as well. [7,8,9] Obviously, for an experimental validation an accurate experimental determination is important. In fact, X-ray tomography can be used to measure a large number of cells with high precision. [10,11,12] From the measured aspect ratio in the cell shape the anisotropy in the stiffness in tension was calculated in agreement with experiments. [11] In addition, by accounting for the anisotropy in plastic behavior the peak stress and strain have been predicted based on a critical strain criterion. [9] In these studies, however, the role of damage accumulation during straining has not been incorporated in the modeling, nor has it been quantitatively measured as a function of density.In a previous study we have shown that damage accumulation starts well before the peak stress has been reached and that the onset and rate of damage evolution depends critically on the base material properties and the relative density of the foam. [13] The ability of the foam to accommodate the applied strain by strut bending and reorientation was identified as an important mechanism responsible for the large peak strain at small densities. The objective of this paper is to study the effect of cell shape anisotropy looked upon in the light of these mechanisms. We start by relating the yield stress to the cell orientation at small strains, followed by a study of the damage evolution at large strain by measuring the electrical resistance in-situ.The material used is ERG Duocel open cell aluminum foam (20 PPI, alloy AA6101). The relative densities of the samples are grouped according to the following three ranges: 3-5 % (low), 6-7 % (medium) and 10-13 % (high). The relative density of each sample was calculated by measuring the mass and dividing it by the volume and the mass of pure Al (2.7 g/cm 3 ). The samples were received in the annealed (AN) condition (3 hrs at 412°C, followed by slow cooling to 260°C and maintaining that temperature for 0.5 hr followed by slow cooling to RT). Some of the samples were subjected to an additional precipitation hardening heat treatment (HT) to increase the yield stress. First the samples were exposed to a solid solution heat treatment (527°C for 8 hrs) followed by quenching in RT water. After 16 hrs at RT the samples were artificially aged for 8 hrs at 177°C, followed by cooling inside the furnace. Table 1 shows the mechanical properties in tension of the Al a...

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“…The yield stress ratio obtained in compression is 1.56 Ref. [13,16] for both heat treatments. The measured aspect ratio of the cell shape is 1.43 ± 0.15.…”

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confidence: 87%

“…These observations suggest that the increase in peak strain in the TD is caused by a decrease in damage accumulation and an increase in the tolerance (final resistance at failure). In our recent study [16] we have correlated these observations to an increased contribution of strut bending to the overall deformation, quantified by q (See Eq. 1).…”

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The Influence of Cell Shape Anisotropy on the Tensile Behavior of Open Cell Aluminum Foam

et al. 2008

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“…In contrast to polymer foams, there is no official standard for testing metal foams. According to results reported elsewhere [12][13][14] and the existing polymer foam standards, [15] tensile specimens should have a minimum strut number per diameter in the gauge length of 6 to 7, and compressive specimens should be longer and wider than seven times the pore diameter. One of the designed tensile specimens is shown in Figure 1.…”

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confidence: 99%

Pummelos as Concept Generators for Biomimetically Inspired Low Weight Structures with Excellent Damping Properties

Fischer¹,

Thielen²,

Loprang³

et al. 2010

Adv Eng Mater

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Natural materials often exhibit excellent mechanical properties. An example of outstanding impact resistance is the pummelo fruit (Citrus maxima) which can drop from heights of 10 m and more without showing significant outer damage. Our data suggest that this impact resistance is due to the hierarchical organization of the fruit peel, called pericarp. The project presented in the current paper aims at transferring structural features from the pummelo pericarp to engineering materials, in our case metal foams, produced by the investment casting process. The transfer necessitates a detailed structural and mechanical analysis of the biological model on the one hand, and the identification and development of adequate materials and processes on the other hand. Based on this analysis, engineering composite foam structures are developed and processed which show enhanced damping and impact properties. The modified investment casting process and the model alloy Bi57Sn43 proved to be excellent candidates to make these bio‐inspired structures. Mechanical testing of both the natural and the engineering structures has to consider the necessity to evaluate the impact of the different hierarchical features. Therefore, specimens of largely varying sizes have to be tested and size effects cannot be ignored, especially as the engineering structures might be upscaled in comparison with the natural role model. All in all, the present results are very promising: the basis for a transfer of bio‐inspired structural hierarchical levels has been set.

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“…Nearly all investigations to date on the mechanical behaviour of metal foams have been conducted on commercial materials such as closed-cell Alporase [1][2][3][4][5][6][7][8][9][10][11][12][13] or Alulighte [4,10,11,[14][15][16] foams, or open-cell Duocele [4,7,[17][18][19][20] aluminium foam. These materials differ in nature and properties; however, a common feature is that all are composed of relatively large cells, generally between 1 and 10 mm in diameter.…”

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confidence: 99%

Hole and notch sensitivity of aluminium replicated foam

2011

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The influence of strain-induced damage on the mechanical response of open-cell aluminum foam

Cited by 54 publications

References 12 publications

The Influence of Cell Shape Anisotropy on the Tensile Behavior of Open Cell Aluminum Foam

The Influence of Cell Shape Anisotropy on the Tensile Behavior of Open Cell Aluminum Foam

Pummelos as Concept Generators for Biomimetically Inspired Low Weight Structures with Excellent Damping Properties

Hole and notch sensitivity of aluminium replicated foam

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