In the new book Why Things Break: Understanding the World by the Way It Comes Apart (Harmony Books, $24), Mark Eberhart, a chemistry professor at the Colorado School of Mines, explores the fascinating question of what holds things together, what breaks them apart, and why we should care. His interest in the topic started early. When he was growing up in the 1960s, Eberhart learned that splitting an atom leads to an awfully big boom. That prompted him to fret that when he cut into a stick of butter, he would inadvertently cause an atomic explosion. In a recent E-chat, the professor talked about the sinking of the Titanic, the fragility of bike locks, and the feasibility of superhero costumes.
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Next News: Which breakage phenomenon do you find most fascinating?
Eberhart: The examples I find most interesting are those dealing with the behavior of some metals at low temperatures. While this is not characteristic of all metals—copper and nickel, for instance—some metals like steel become brittle at low temperatures. Exactly how low depends on the exact composition of the metal in question.
The steel in the Titanic provides an illustration as to how catastrophic this brittle behavior can be. Because the ship’s steel was high in sulfur impurities, it became brittle at comparatively modest temperatures. In the freezing water of the north Atlantic the hull of the ship was quite brittle, and it was this fact that accounted for the extensive damage done to the ship when hitting the iceberg.
Then there is the common bicycle lock, which is often made from very hard steel so that is cannot easily be cut with a bolt cutter. However, if the lock is cooled by pouring liquid nitrogen over it, a modest hammer blow will cause the lock to break. What is most interesting, to me, is that though we know about these phenomena, we still do not know exactly why some materials show the decrease in toughness with temperature while others do not.
Another effect that is interesting is the reduction in toughness due to the presence of impurities—small amounts of mercury, for example, make aluminum simply fall apart. This is the reason mercury thermometers are not allowed on airplanes. Airplanes are made from aluminum.
Next News: What role will nanotechnology play in better material design and manufacture?
Eberhart: Nanotechnology has not yet begun to have an effect on materials design and manufacture. However, in the years to come this technology will drive miniaturization, which will be particularly important in medical and life sciences. Also, as nanomachines will need to be manufactured to amazing tolerances, this will have an effect on the overall quality of manufactured goods.
Next News: What are the remaining great mysteries or great challenges of material science?
Eberhart: The great mysteries of materials science remain the full elucidation of the relationships between structure of materials and properties. From observations of natural materials, we know that ultimate properties are far beyond anything we have obtained. Spider silk is hundreds of time stronger than the best synthetic fibers. Though we know this to be true, the reasons remain hidden. Once these relationships are exposed, it will be possible to design materials with phenomenal properties.
Next News: OK, then, is it possible to create a fabric a light as silk but completely bulletproof—kind of like Captain America's costume?
Eberthart: Well, yes, it is probably possible to make a fiber that could not be penetrated by a bullet. However, this would not help the wearer much. The bullet would still transfer momentum to the wearer, causing damage without penetrating. It seems that the properties of light, flexible fabrics are incompatible with protective garments.