A team of engineers at the Massachusetts Institute of Technology (MIT), led by K. Jem Tasan, found out why steel razor blades dull when shaving, despite the fact that they are 50 times harder than hair. With the help of an electron microscope, they found that under certain conditions, even a single hair could break off the edge of a blade.
According to the researchers, we are not talking about simple wear of the metal, as in the case of friction, for example, about a whetstone. This process looks much more complicated. The metal of the razor, with frequent "incorrect" contact with the hairs, experiences stress, which leads to the formation of cracks and chips - that is, in fact, to wear of the cutting edge (dullness).
To learn more about the processes taking place during shaving, MIT graduate student Gianluca Roschioli shaved with a disposable blade and then examined its surface under an electron microscope. As a result, he found slight but visible wear, with the chips being along the edge of the blade.
For a more complex test, Roscchioli designed a micromechanical apparatus consisting of a movable block and two clamps for holding the blade and fixing test hairs of various diameters, provided by his colleagues specifically for the experiments. During the experiments, the device cut at different depths and at different angles, while being in the field of view of the electron microscope.
Analysis showed that the blades did not chip when the hairs were cut perpendicularly. However, everything changed when the cuts were made at an angle - the number of chips increased. Computer simulation has shown that not only the angle of inclination is important, but also the density of the steel in the blade.
In order to improve the quality of the blades, the researchers applied for a patent to make razor steel more uniform.