Case Study: The Beryllium Bicycle Frame

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A $25, 000 bicycle frame? That's the cost of the materials, not including labor. The total weight of the frame is 2.5 pounds, of which the beryllium tubes contribute 1.0 pounds. The remaining weight is due to the aluminum lugs and adhesive. This one of a kind bike is made out of beryllium, a super light and super stiff metal. Formally, it was used for aerospace projects, particle beam accelerators, experimental fusion reactors, x-ray machines, and inertial guidance systems of most missiles.

Beryllium is the fourth element on the periodic table, and is far lighter than materials traditionally used for bicycle frames (see Table 1). Its stiffness exceeds that of all other metals, most carbon fiber composites, and even SiC reinforced aluminum. The specific modulus (ratio of stiffness to density) is seven times better than steel, titanium, or aluminum.

Beryllium's tensile strength falls between high-strength aluminum and steel-titanium alloys, but it's so light that alloying to increase the strength still results in a structure that weighs very little.

Why can't the average consumer obtain this bike frame? Eventhough the stiffness, density, and tensile modulus are great, the price for an ounce of Be is about $300!! This translates into $19, 200 for one pound of material!! Current research is being conducted on aluminum-Be alloys called "albemet" to help reduce the cost while retaining the super properties. Albemet is an alloy of 38% aluminum and 62% beryllium. This alloy splits the difference between elemental beryllium and the other metals, still leaving it lighter and several times stiffer than the other bicycle frames. It is also easier to weld, and should reduced the cost to about 1.5 times that of a titanium bike frame. Table 1 Material Density (g/cm3) steel 7.87 titanium 4.51 aluminum 2.70 beryllium 1.85

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Author:
Roberta Dean
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