How hair deforms steel

Abstract

Steels for sharp edges or tools typically have martensitic microstructures, high carbide contents, and various coatings to exhibit high hardness and wear resistance. Yet they become practically unusable upon cutting much softer materials such as human hair, cheese, or potatoes. Despite this being an everyday observation, the underlying physical micromechanisms are poorly understood because of the structural complexity of the interacting materials and the complex boundary conditions of their co-deformation. To unravel this complexity, we carried out interrupted tests and in situ electron microscopy cutting experiments with two micromechanical testing setups. We investigated the findings analytically and numerically, revealing that the spatial variation of lath martensite structure plays the key role leading to a mixed-mode II-III cracking phenomenon before appreciable wear.

The homogenous alternative to biomineralization: Zn- and Mn-rich materials enable sharp organismal “tools” that reduce force requirements

“…The main advantage of the zinc-and manganese-materials, relative to the tested biomineralized materials, is likely their homogeneity, which may enable sharper and more precisely shaped structures since HEBs do not have mineral inclusions. In addition, the homogeneity of HEBs relative to biomineralization, may reduce chipping damage like that found along razor blades at boundaries between grains of differing stiffness 112 .…”

Recent Progress on Wear‐Resistant Materials: Designs, Properties, and Applications

“…Steel tools with martensitic microstructures for high hardness cannot cut soft materials such as human hair, cheese, and potatoes, which can be attributed to the hierarchical structures of the interacting materials and the dynamic boundary conditions of their co‐deformation. [ 163 ] Haircutting causes nucleation, propagation, and coalescence in the hard lath martensite. Such failure processes occur through the collective effects of i) out‐of‐plane shear stresses resulted from hair bending, ii) the asperity on the cutting edge with different microstructures on either side, and iii) contact alignments between an asperity and the outermost circumferential point of hair.…”

Evolution of Eutectic Carbide during M7C3/M23C6 in situ Transformation in Martensitic Stainless Steel

“…These carbides range from a few micrometers to tens of micrometers in size, and they are prone to chipping, bluntness, breakage, and rust of knife edges. [ 3–5 ]…”