Human hair is 50 times softer than steel, yet it can chip away a razor?s edge, a new study shows.
Razors, scalpels, and knives are commonly made from stainless steel, honed to a razor-sharp edge and coated with even harder materials such as diamond-like carbon. However, knives require regular sharpening, while razors are routinely replaced after cutting materials far softer than the blades themselves.
Now engineers at MIT have studied the simple act of shaving up close, observing how a razor blade can be damaged as it cuts human hair ? a material that is 50 times softer than the blade itself. They found that hair shaving deforms a blade in a way that is more complex than simply wearing down the edge over time. In fact, a single strand of hair can cause the edge of a blade to chip under specific conditions. Once an initial crack forms, the blade is vulnerable to further chipping. As more cracks accumulate around the initial chip, the razor?s edge can quickly dull.
The blade?s microscopic structure plays a key role, the team found. The blade is more prone to chipping if the microstructure of the steel is not uniform. The blade?s approaching angle to a strand of hair and the presence of defects in the steel?s microscopic structure also play a role in initiating cracks.
The team?s findings may also offer clues on how to preserve a blade?s sharpness. For instance, in slicing vegetables, a chef might consider cutting straight down, rather than at an angle. And in designing longer- lasting, more chip-resistant blades, manufacturers might consider making knives from more homogenous materials.