Fatigue and Kinetics of Repeated Grooming
What Causes Hair to Break; Fatigue and Kinetics of Repeated Grooming
Breakage is one of hair care industry’s greatest issues as it leads to the production of unsightly split ends. Historically, the tendency for fibers breaking was assessed using constant rate extension experiments to generate stress-strain curves – yet our pioneering work with single fiber fatigue experiments can often lead to different conclusions. Most notably, fatigue experiments generally produce considerably larger differences between samples – possibly suggesting that, until now, we have been underestimating the effects of deleterious treatments. The adoption of general fatigue testing principles produces a model for understanding the relative magnitude of causes/contributors to hair breakage – while also suggesting routes for mitigation. Further, the adoption of data analysis methods commonly used in this field produces novel new product communication methods. On-going work involves further testing and refinement of this model though additional cause and effect experiments.
Diastron CYC 801 Single Fiber Fatigue Tester
S-N Plots for Virgin Caucasian Hair Versus Panelist Hair
Stress vs Number of cycles‐to‐fail (S‐N) Scatter Plots showing the increased tendency for
breakage at hair tips procured from a panelist.
Failure Cycles Versus Stress Virgin Hair
S‐N Plots showing the sizable dependence of relative humidity on the tendency for hair
breakage under fatiguing conditions.
Survival Probability Plots for Virgin Caucasian Hair at 60% Relative Humidity
Fatigue results can also be used to model the likelihood of breakage under differing
conditions ‐ which has allowed for identification of contributing parameters that previously might not
have been considered.
Weibull Modeling of Breakage Data Versus Experimental Data
for Repeated Grooming Testing on Damaged Hair
This same modeling can be applied to repeated grooming experiments (which also represent
a fatiguing stimulus) to provide novel communication stories.
T.A.Evans, Fatigue Testing of Hair – A Statistical Approach to Hair Breakage, Journal of
Cosmetic Science, 60, 599-616, Nov/Dec, 2009
T.A.Evans and K.Park, A Statistical Approach to Hair Breakage. II. Repeated Grooming
Experiments, Journal of Cosmetic Science, 61, 439-455, Nov/Dec, 2010
A Unified Theory for Visualizing the Causes of Hair Breakage