How hair deforms steel

Gianluca Roscioli; Seyedeh Mohadeseh Taheri-Mousavi; Cemal Cem Tasan

doi:10.1126/science.aba9490

How hair deforms steel

Science. 2020 Aug 7;369(6504):689-694. doi: 10.1126/science.aba9490.

Authors

Gianluca Roscioli¹, Seyedeh Mohadeseh Taheri-Mousavi^{1

2}, Cemal Cem Tasan³

Affiliations

¹ Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
² Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
³ Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA. tasan@mit.edu.

PMID: 32764070
DOI: 10.1126/science.aba9490

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.