Berkeley Engineering

Spring 2003


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Getting to know your bike atom by atom

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Devine photo

Matt Sherburne (left) and Tom Devine

Getting to know your bike atom by atom

Pedaling 16 hilly miles from Moraga to the Berkeley campus and back — a daily journey Professor Tom Devine made rain or shine for a year — gave the materials science and engineering professor ample opportunity to plan a class using his bike to teach basic engineering concepts.

The result: MSE 24, a popular freshman seminar Devine has taught on and off for the past nine years. "Biking is a good way to teach the fundamentals of engineering systems and engineering design," says Devine. "No one is intimidated when you talk about bikes."

Last fall a relaxed group of 18 students met weekly with Professor Devine, to tear down and reassemble bikes, peer at parts under a microscope, then analyze the materials for hardness, strength, impact loading, resistance, and metal fatigue. Their analyses led to their final project: select resilient materials, then design a "perfect" bike.

"How many parts does your bike have?" Devine asks. "Would you believe more than a thousand?

Chao photo
Julie Chao

The closer you look at the bike, the more you realize how many parts there are and how they function," he tells the students, who will soon be afloat in hundreds of parts, from rims, spokes, bushings, and tierods, to brake levers, steering tubes, and aluminum lugs.

Matt Sherburne, MSE graduate student, former bike racer, and Devine’s graduate assistant, says, "In this class we talk about why the components work the way they do. When we talk about spokes, we talk about ‘Euler’ buckling and why a bicycle wheel is built with the spokes in tension, unlike the old wagon wheels built with the spokes in compression. Now the students understand the engineering principles that go into making a wheel, and why and where steel or aluminum frames sometimes break."

Chan photo
Vincent Chan

"I’m interested in the molecular level of materials," says Julie Chao, having just completed a set of metal impurities tests. Sometimes, she says, impurities can strengthen a metal. "At the molecular level, all the atoms are next to each other. To make a dent, the atoms have to break the bond and form another bond with the atom right next to it. When an impurity gets into a metal, the atoms around it can’t move as easily as if it was a pure metal. So the bond of the atoms around the impurities can be harder to break."

Zmugg photo

Stephan Zmugg

Mountain biker and ChemE freshman Vincent Chan sawed quarter-inch lengths of metal tubing, sampling carbon and low-alloy steel, aluminum, and titanium — the metals used in bike frames — testing them using the Rockwell hardness tests.

After heating the steel samples to 800°C, and the titanium tubes to 1,000°C, Chan quenched some of the red hot samples in oil, to cool them slowly. He quenched others in water, to cool them rapidly, before testing both batches. "Freshman seminars are different from other courses," says Chan. "They are low pressure classes that encourage students to interact more with professors."

BioE major Stephan Zmugg took his turn smashing a piece of low-alloy steel tubing that had been heated, then plunged into a vat of liquid nitrogen at a frigid –196°C for 15 minutes. Smash tests help assess whether or not a frame has core resistance to impact.

"We want to know if the metals behave like glass or taffy," says Devine explaining the test. "What we want is taffy, for a ductile, tough material. It’s a simple binary test. You grab the sample, drop it, smack it, and either it breaks or it doesn’t."

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