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Human hair is about 50 times softer than a razor blade, which is made using heat-hardened stainless steel and often reinforced with diamond-like carbon. Yet, a few wisps of hair are powerful enough to dull a blade's sharpness within a few weeks of use. To understand how this impressive feat occurs, a team of researchers from the Massachusetts Institute of Technology (MIT) decided to take a closer look at what happens when the sharp edge of a blade slices through human hair.
"We are metallurgists and want to learn what governs the deformation of metals so that we can make better metals," Cem Tasan, a professor of material science at MIT, says. "In this case, it was intriguing that, if you cut something very soft, like human hair, with something very hard, like steel, the hard material would fail."
The team, which included graduate student Gianluca Roscioli, devised a string of experiments to keep track of the rate at which a razor blade deteriorated after each consecutive shave. The scientists found that when the blade was placed perpendicular to the hair, it sustained no damage. However, if the hair was cut at an angle, even a single strand could chip the edge of the razor blade. Once the initial crack formed, the blade became increasingly vulnerable to further chipping, accelerating its dulling. Another contributing factor was the uniformity of the microstructure of the steel from which the blade was made. Even slight imperfections could cause the blade to crack when it came in contact with the hair.
"Our initial thought was that this was a wear problem, that material was being removed from the razor," Tasan says. "We were expecting to see that over time the blade gets rounder and rounder. We didn't see it." Instead, he continues, "We saw fracturing and chipping of the blade that is forming this C-shaped crack."
The MIT scientists, who published the findings in the journal Science on August 6, 2020, hope to conduct further research to help them to develop longer-lasting blades. They have even filed for a patent for a new manufacturing process to make razor blades harder by compressing the metal instead of heating and sharpening it, as is currently the norm. Though more expensive than conventional blades, the durable models would prove economical in the long run and also be better for the environment since fewer would be tossed in the trash. "I really believe we can build a better blade," Roscioli says.
While the study was conducted on razor blades, the researchers believe the findings could be helpful in not only creating better knives, but also retaining the sharpness of the ones you currently have. Their advice? When slicing vegetables, cut straight down instead of at an angle!
Resources: Smithsonian.org, news,mit.edu.