Shaving blades are made of stainless steel and coated with even harder materials such as diamond-like carbon. This is the reason why shaving blades are 50 times harder than human hair. Despite its superior hardness, blades become dull after repeated usage.
It has always been thought that edge rounding and brittle cracking of a blade’s hard coating were responsible for shaving blades losing their sharpness.
Now, researchers at MIT found that the act of shaving deforms the blade in a way that is more complex than simply wearing down the edge over time.
A single strand of hair, they found, can cause the edge of a blade to crack due to out-of-plane bending, microstructure of the steel not being uniform and microscopic chips along the smooth edge of the blade. 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 researchers found that chips did not occur when the hair was cut perpendicular to the blade but only when it cut the hair at an angle and when the blade edge met the sides of the hair strands.
Regardless of a hair’s thickness, in the experiments, the mechanism by which the hair damaged a blade was the same — the edges of the blade were getting chipped but the chipping was occurring only in certain spots.
