182. structure and mechanical behavior of human hair

Department: NanoEngineering
Faculty Advisor(s): Marc A. Meyers

Primary Student
Name: Yang Yu
Email: yay047@ucsd.edu
Phone: 858-263-6144
Grad Year: 2017

Abstract
The understanding on the mechanical behavior of hair under various conditions broadens our knowledge in biological materials science and contributes to the cosmetic industry. The hierarchical organization of the hair is studied from the intermediate filament to the structural levels. The effects of strain rate, relative humidity, and temperature are evaluated. Hair exhibits a high tensile strength, 150-270 MPa, which is highly dependent on strain rate and humidity. The strain rate sensitivity, approximately 0.06-0.1, is comparable to that of other keratinous materials and common synthetic polymers. The structures of the internal cortex and surface cuticle are affected by the large tensile extension. One distinguishing feature, the unwinding of the α-helix and the possible transformation to β-sheet structure of keratin under tension, which affects the ductility of hair, is analytically evaluated and incorporated into a constitutive equation, which agrees with the experimental results. This model elucidates the tensile response of the α-keratin fibers. The contributions of elastic and plastic strains on reloading are evaluated and correlated to structural changes.

Industry Application Area(s)
Materials

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