HAIR STRENGHT TEST

Hair Strength Test measures hair's resistance to breakage, splitting, and other forms of damage. These tests evaluate hair's overall health, structural integrity, and resilience to various treatments such as chemical processing, heat styling, and brushing. They are widely used by cosmetic product developers, hair care specialists, and researchers to assess product efficacy, analyze hair damage, and compare different hair types.

Common Methods Used in Hair Strength Testing

1. Tensile Test

• Technical Details: The most fundamental hair strength test. A single hair strand is clamped between the grips of a universal testing machine (e.g., Instron) and stretched at a constant elongation rate until it breaks.

• Measured Parameters:

  • Breaking Strength (Tensile Strength): The maximum force a hair strand can withstand before breaking (measured in Newtons or gram-force). This indicates hair’s overall strength.

  • Elongation at Break: The percentage increase in hair length before breaking, reflecting its flexibility and brittleness.

  • Young’s Modulus (Elastic Modulus): Represents the stiffness of the hair under tension. It is derived from the slope of the initial linear region of the stress-strain curve.

  • Work to Break (Toughness): The total energy required to break the hair, calculated as the area under the stress-strain curve. This parameter combines strength and flexibility.
    
    

2. Cyclic Tensile Test (Fatigue Test)

• Technical Details: Evaluates hair’s resistance to repeated stress. A hair strand is subjected to cyclic loading and unloading until it breaks.

• Purpose: Simulates the effects of everyday grooming practices such as brushing, combing, and heat styling.

• Measured Parameters: The number of cycles the hair strand can endure before breaking.
  
  

3. Bending Test

• Technical Details: Measures the hair strand’s resistance to bending forces. The strand is bent to a specific radius or wrapped around a test apparatus to observe any breakage.

4. Abrasion Test

• Technical Details: Used to measure the hair strand's resistance to friction. The hair strand is rubbed against a known surface under a specified load, and the amount of wear is evaluated.

• Purpose: Assesses the damage caused by brushing and other mechanical processes on the hair surface.
  
  

5. Torsion Test

• Technical Details: Measures the hair strand's resistance to twisting forces. One end of the hair strand is fixed while the other end is twisted. The angle of breakage and the applied torque (twisting force) are measured.

• Purpose: Evaluates the flexibility and brittleness of the hair.
  
  

Factors Affecting Hair Durability

• Hair Structure: The cortex (main structural component), cuticle (protective outer layer), and medulla (inner core) all influence hair's durability.

• Moisture Content: The moisture content of the hair significantly impacts its flexibility and brittleness.

• Chemical Treatments: Processes such as coloring, perming, and straightening can weaken the hair structure.

• Heat Styling: High temperatures can damage hair proteins, making the hair more brittle.

• Genetic Factors: The natural structure and durability of hair are determined by genetics.

• Nutrition and Health Status: Poor nutrition and certain health conditions can lead to weakened hair.