Deformation Mechanisms in Gum MetalDaryl C. Chrzan, University of California, Berkeley, DMR 1105081

Gum metals display a host of “super” properties including super-elasticity and super-strength. Presently, the deformation mechanisms underlying these properties are not yet known. This knowledge is essential to developing new alloys with Gum Metal like behavior.In our work, we have shown using a simple model that the predominant microstructural feature in Gum Metals, the so-called nanodisturbances, are a natural result of the near annihilation of oppositely signed dislocations in these materials, and do not mediate slip as believed previously. Moreover, we believe that we have identified the obstacles preventing dislocation annihilation: nanoscale second phase precipitates produced during the cold-working of these alloys. We believe that the super-elasticity observed in these alloys arises from the reorientation of the preferred axis of these precipitates.

(top) A comparison of the nanodisturbance structure observed by Gutkin et al., Acta Mat. 2006 and the predictions of our Frenkel Kontorova model. The positions of the blue atoms track those of the columns of atoms in Gum Metal quite well given the simplicity of the model. (bottom) Our high resolution image of the second phase particles observed using the TEAM 0.5 microscope at NCEM. The local diffraction pattern shows the presence of the HCP phase within a region spanning a few nanometers.

Physics and Materials Science of SkateboardingDaryl C. Chrzan, University of California, Berkeley, DMR 1105081

We have continued our efforts to raise awareness of Materials Science and Engineering amongst a broader community by developing course materials showing how Materials Science and Engineering influences the sport of skateboarding.Briefly, the rise of skateboarding as a sport is a materials science story. It was not until the introduction of urethane as a wheel material that the sport began to evolve towards its current state.We have developed course materials for a freshman seminar course titled “Physics and Materials Science of Skateboarding.” These materials include a discussion of the materials science aspects of the sport, as well as experiments that can be adapted for use in high school physics courses. We have begun to make these materials available on the web to anyone that chooses to make use of them.

Figure illustrating the distortion of a skateboard wheel under the weight of the rider. As the wheel rolls, it is constantly compressing and decompressing. If the decompression rate is too slow, the wheel will decompress when it is no longer in contact with the ground, and one loses all of the energy expended in compressing the wheel. If the wheel decompresses rapidly, then it will push against the ground, and return the compression energy to the rider. This ability to react quickly is known as resilience. Urethane is soft yet highly resilient, so it makes a good material for a wheel. More details can be found at:

http://chrzan.mse.berkeley.edu/skateboarding

(This web site is still under construction.)