How hair deforms steel

Abstract

A hair-splitting way to get dull Razors eventually become dull after shaving even though the blade is about 50 times harder than the hair. Whereas edge rounding and brittle cracking of a blade's hard coating were thought to be responsible, a detailed microstructural investigation by Roscioli et al. shows a different mechanism. A combination of out-of-plane bending, microstructural heterogeneity, and asperities—microscopic chips along the smooth edge—sometimes caused fracture to occur if the conditions lined up. This fracture originated at the hair-edge asperity interface and created chipping that dulled a blade faster than other processes. Science , this issue p. 689