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Strike Up the Bands

In the ongoing quest for stronger materials, the challenge is not simply to find materials that are very strong and stiff, but also materials that are tough. The reason we build airplanes out of metals, and not ceramics, for example, is that they fail gracefully -- they can give without breaking. The development of bulk metallic glasses represented a breakthrough in producing metals of exceptional strength and elasticity. However, when pushed just beyond the limit of their elastic limit they fail dramatically.

Scientists in IRG II aim to understand how this failure takes place in order to control and even suppress it. They have developed a new way to see the formation, structure, and motion of the localized bands of deformation, "shear bands," that appear when a metallic glass is pushed beyond this limit. Electron microscopy performed in-situ during deformation reveals the nano-scale structure of individual bands and the patterns they form (see TEM IMAGES at right of "in-situ" shear bands in a glass matrix -- dark field, top, and bright field, bottom). This new capability will be used to explore strategies to inhibit catastrophic propagation of shear bands and encourage multiple shear banding. Ultimately, this could produce materials with twice the strength and elasticity of ordinary metals combined with the "toughness" of the best engineering metals.

For further information, please contact Professor Bill Johnson, team leader of IRG 2: (626) 395-4433 or wlj@caltech.edu.

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