HAIR BREAKAGE: REPEATED GROOMING EXPERIMENTS 455 application conditions. Nevertheless, experiments herein illustrate the considerable ef- fects of conditioning, chemical damage, and the relative humidity of the environment on the propensity for fi ber breakage. It is also shown how the two Weibull parameters, to- gether with information about the number of fi bers in the test tresses, allow for the modeling of repeated grooming testing and allow investigators to re-create the experi- mental outcome for comparison to their own experiences. Preliminary experiments also examined the nature of the generated fi ber fragments. The appearance of small fragments (resulting from breakage near the hair tips) occurs accord- ing to a “wear out” mechanism, by which an increased number of grooming strokes leads to an increased rate of formation. However, the diminished occurrence of longer frag- ments with increased grooming indicates a “premature failure” mechanism, which may be explained in terms of the gradual brushing out of snags and tangles. ACKNOWLEDGMENTS The authors thank Carl Gorman and Chuck Farina for fabrication of the automated grooming device used in this work. REFERENCES (1) C. R. Robbins, The Chemical and Physical Behavior of Human Hair, 4th ed. (Springer-Verlag, New York, Heidelberg, 1988), Ch. 8. (2) W. Hamburger, H. M. Morgan, and M. M. Platt, Some aspects of the mechanical behavior of hair, Proc. Sci. Sect., 14, 10–16 (1950). (3) A. C. Brown and J. A. Swift, Hair breakage: The scanning electron microscope as a diagnostic tool, J. Soc. Cosmet. Chem., 26, 289–297 (1975). (4) C. Robbins, Hair breakage during combing. I. Pathways to breakage, J. Cosmet. Sci., 57, 233–243 (2006). (5) C. Robbins, Hair breakage during combing. II. Impact loading and hair breakage, J. Cosmet. Sci., 57, 245–257 (2006). (6) C. Robbins and Y. Kamath, Hair breakage during combing. III. The effects of bleaching and conditioning on short and long segment breakage by wet and dry combing of tresses, J. Cosmet. Sci., 58, 477–484 (2007). (7) C. Robbins and Y. Kamath, Hair breakage during combing. IV. Brushing and combing hair, J. Cosmet. Sci., 58, 629–636 (2007). (8) T. A. Evans, A statistical analysis of hair breakage, J. Cosmet. Sci., 60, 599–616 (2009). (9) W. Weibull, A statistical distribution function of wide applicability, J. Appl. Mech, 9, 293–297 (1951). (10) S. B. Hornby, Cyclic testing: Demonstrating conditioner benefi ts on damaged hair, Cosmet. Toiletr., 116, 35–39 (2001). (11) S. B. Hornby, N. J. P. Winsey, and S. P. Bucknell, New techniques to capture viscoelastic changes in hair induced by mechanical stress, IFSCC Magazine, 5(2), 93–97 (2002). (12) B. Dodson, The Weibull Analysis Handbook, 2nd ed. (American Society for Quality Press, Milwaukee, 2006), Ch 1.