Basically the paper discusses the possibility of a dynamic collapse mechanism in metal foams produced via a blowing agent route. The example is aluminum foams. The arguments supporting it are sparse, but have led me to suggest some additional dynamic mechanism that might influence stability of these foams during expansion. The idea is that expansion means increase of pore size, which means stretching of cell walls. This stretching may (at least on traditional assumption) reach a limit once a cell wall thickness of approximately 50-70 µm is reached. Below this threshold, the cell wall is not stable, reaching the limit can be via drainage.
My additional assumption was that if the liquid film (which the cell wall finally is) is simply stretched fast, there may be a "speed limit" above which local thinning is not compensated by material redistribution (= flow) within the cell wall any more.
My only basis for this is "common sense" (a dangerous tool) and the observation of a link between collapse and gas evolution rates, the latter simulated.
This is a weak basis of course. I could - out of hand - imagine two ways of studying the issue: One would be via looking at the behaviour of thin metal films (as they are studied by Francisco Garcia-Moreno's group in Berlin) not in a static state, but when being stretched in a controlled manner. The other would be via simulation of flow within a cell wall: What should happen if there is a local thinning and the metal film is stretched at different speed levels ? The latter might not give the true "speed limit", as the system is not known well enough in detail (see role of oxides in metal foam stability etc.), but it might either support or contradict the existence of a limit as such.
Finally, there might be studies done in other contexts which I did not find when writing the paper, so any input is welcome
I don't have funds, resources or anything at the moment to follow up on this, I am asking out of mere scientific curiosity.
Thanks for any contribution to this ...
Best regards,
Dirk Lehmhus
Article Dynamic Collapse Mechanisms in Metal Foam Expansion
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