Structure and mechanical behavior of human hair

Area of Science:

• Biological materials science
• Biophysics
• Cosmetic science

Background:

• Hair's mechanical behavior is crucial for understanding biological materials and the cosmetic industry.
• The hierarchical structure of hair, from intermediate filaments to macroscopic levels, influences its properties.

Purpose of the Study:

• To investigate the mechanical behavior of hair under varying strain rates, relative humidity, and temperatures.
• To develop a constitutive model that incorporates structural changes in keratin under tension.

Main Methods:

• Tensile testing of hair specimens under controlled environmental conditions.
• Analytical evaluation of structural transformations (alpha-helix to beta-sheet) during deformation.
• Development and validation of a constitutive equation based on experimental data.

Main Results:

• Hair exhibits high tensile strength (150-270 MPa), significantly influenced by strain rate and humidity.
• Strain-rate sensitivity of hair (0.06-0.1) is comparable to other keratinous materials and synthetic polymers.
• A validated model accurately describes the tensile response of alpha-keratin fibers, correlating elastic and plastic strains with structural changes.

Conclusions:

• The mechanical properties of hair are complex and sensitive to environmental factors and loading conditions.
• Understanding keratin's structural transitions under tension is key to predicting hair's ductility and mechanical response.
• The developed model provides a robust framework for analyzing hair's tensile behavior and its underlying structural dynamics.