You would not assume that there would be anything intense going on between the razor you point at your skin and the hair. Although, a group of scientists wondered what's the deal with razorblades going more and more blunt with each use. The investigation yielded rather interesting insights.
A strand of hair is roughly 50 times as soft as a razor blade. Still, a single hair is able to chip at the razor. And once an initial chip forms at the blade, the blade becomes more and more vulnerable to further chippings with each strand cut. Once enough of these chips accumulate around the razor's edge, the blade becomes blunt.
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The key point here is the structure of the blade, scientists found. The blades become more prone to getting chipped if the steel's microstructure is not even throughout the blade.
The team also had some insights into how to preserve a blade's sharpness. Cem Taşan, an Associate Professor of Metallurgy at MIT says, “Our main goal was to understand a problem that more or less everyone is aware of: why blades become useless when they interact with much softer material,” and adds, “We found the main ingredients of failure, which enabled us to determine a new processing path to make blades that can last longer.”
To find an answer, Roscioli, an MIT graduate, put together a contraption to create a more controlled environment for testing. The contraption has a movable stage with two clamps that hold on to the hair and the razor. Roscioli carried out the experiment with commercially available razors and tested how they perform from various angles. He found that the faults occur at certain places.
The findings showed that chips occurred the least when the blade was held perpendicular to the hair. When the hair had room to move around though, more faults showed up.
A more important factor was, as mentioned before, the microstructure of the blade. When the blade's alloy was spread more homogeneously, fewer cracks showed up.
Roscioli plans to produce blades that perform better over time in light of these findings, he says “The basic idea is to reduce this heterogeneity, while we keep the high hardness. We’ve learned how to make better blades, and now we want to do it.”