92 Creep of metallic foams

The creep strain response of an open-cell Duocel metallic foam is shown in Figure 9.2. In tension, the response is similar to the schematic of Figure 9.1.

Time (hours)

Figure 9.2 Creep strain plotted against time for open-cell metallic foam under (a) tensile and (b) compressive loading (Duocel open-cell aluminum 6101-T6 foam; Andrews et al, 1999)

Time (hours)

Figure 9.2 Creep strain plotted against time for open-cell metallic foam under (a) tensile and (b) compressive loading (Duocel open-cell aluminum 6101-T6 foam; Andrews et al, 1999)

The primary creep regime is short. The extended period of secondary creep is followed by tertiary creep, terminated by rupture. In compression, the behavior is somewhat different. At the end of secondary creep, the strain rate initially increases, but then subsequently decreases; the increase corresponds to localized collapse of a layer of cells. Once complete, the remaining cells, which have not yet reached the tertiary stage, continue to respond by secondary creep at a rate intermediate to the initial secondary and tertiary rates.

For tensile specimens, the time to failure is defined as the time at which catastrophic rupture occurs. For compression loading, the time to failure is defined as the time at which the instantaneous strain rate is five times that for secondary creep.

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