Nano Focus: New mechanism heals nanocracks in metal under tensile stress
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Focus New mechanism heals nanocracks in metal under tensile stress
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hen a crack forms in a material, typically it is downhill from there onwards. Any further tension makes the crack spread and only increases the damage. At least, that is what intuition and conventional fracture mechanics indicate. Now, the opposite effect has been observed. Under certain circumstances, applying tension or other loading to cracks can actually trigger these fissures to close. “This really turns our understanding of what is possible in fracture mechanics on its head,” said Michael Demkowicz, an assistant professor of Materials Science and Engineering at the Massachusetts Institute of Technology and co-author with graduate student Guoqiang Xu, of an article published in the October 4 issue of Physical Review Letters (DOI: 10.1103/ PhysRevLett.111.145501; 145501). “It’s not surprising if a crack closes under compression, but if you pull on the crack
of the VO2-sapphire system for infrared tagging, camouflage and identification schemes, and the range of possibilities for designer film-substrate systems with specific thermo-optical properties, this paper may well turn out to be Reference Number 1 in many papers yet to come.” “I think that one of the most clever things about this work is that this team saw that the transition region, instead of being a necessary bridge from insulator to metal, could be a region with a wealth of really interesting physics,” said Dan Wasserman, an assistant professor in Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign. “The idea of a naturally occurring, and dynamic, disordered metamaterial is fascinating, and they’ve utilized this transition region to show some really interesting macroscopic features of the material. I look forward to seeing what happens as they continue to explore this material system, in particular at the nanoscale.” Tim Palucka
an object can heat up or cool down is by absorbing or emitting radiation, is another possible application down the road. Kats talks about future plans to modify the VO2 or change the substrate to produce a whole family of structures that could be effective in different circumstances. “We need to be able to do this either over a larger temperature range or at lower temperatures,” he said. “If you want to put this on a person for temperature regulation or for camouflage, you need to do it not at 75°C but 35°C. A lot of this is going to depend on how we can control the system to change the transition temperature.” According to Richard Haglund, Professor of Physics at Vanderbilt University who was not involved in this research, “This paper suggests a broad applications potential for tunable thermo-optical systems based on the complementary properties of a phase-changing film and an appropriately selected or designed substrate. Given the potential
and see it close, that’s very unexpected.” Demkowicz and Xu stumbled across this discovery by accident. While studying hydrogen embrittlement in nickel-based superalloys as part of a
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