Note: This was originally posted on 13 January 2005.
Today, Prof. John Banhart, Chairman of the Department of Materials at Hahn-Meitner Institute Berlin, gave an excellent talk on metal foams, those delightfully weightless wonders. His lecture is indeed a great example of how to present an overview; he covered several aspects of metal foams: (a) how foams can be made, (b) why they might be useful, (c) their actual and potential applications, and (d) the scientific challenges they pose.
The moment Prof. Banhart said he was going to give an overview, my first reaction (which turned out to be rather misplaced -- more on this below) was: "God, are we in for another one of those light weight (please pardon the pun) talks?"; I was delighted to be disappointed! Prof. Banhart showed us how to present an overview without having it perceived as short on scientific content. While his chosen format forced him to spread himself thin by covering a lot of material, he made sure that he said something about the scientific issues in almost every topic.
For example, when he talked about the powder metallurgy route for making aluminium alloy foams (quite a bit like making bread), he showed an X-ray video of the process of foaming, which indicated large, almost crack-like pores that appeared first. His commentary for the video went like this: "Look, this is an important issue because it will have a bearing on the properties. We have done some work to understand why this happens, and what can be done to ensure the initial pore formation is more uniform, and more rounded". He did eventually cover these issues when his talk turned to the open scientific issues.
Similarly, in the section on properties of foams, he first showed the stress-strain response of foamy materials, followed by how these properties can be exploited in particular ways: light weight (stiffness per unit weight and unit thickness), high energy absorption during impact (at efficiency levels as high as 85 %) and better damping of vibrations. He gave specific examples of applications (those that are in wide use as well as those that are at the prototype or demonstration stage). Once again, he used science and mechanics based arguments to show why these applications make sense.
What was absolutely impressive was Prof. Banhart's rather disarming way of lightening (pardon the pun again; "light" seems to be the word of the day for me) the talk. For example, he showed a video of a coffee cup that remained a coffee cup after falling on a piece of metal foam, but shattered when it fell on the floor; after the video, he said, "Now you know why foams are so attractive as construction materials; they will protect your coffee cups!". Another example of his disarming charm was on display when he revealed that he doesn't believe now some of the things he said 5 to 10 years ago (in journal articles, no less!) and, by the same token, he may not believe -- say, five years from now -- some of the things he said in today's seminar!
All in all, it was a wonderful lecture. It was well worth coming to work on a Saturday morning!
Just a couple of quick links to sites with more information on metal foams: Metal Foams section of HMI, and the metalfoam.net.
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