Fatigue testing of hair-a statistical approach to hair breakage

The objective of this work is to describe an alternative approach for assessing hair breakage. The methodology involves the repeated application of force, together with an evaluation of the number of cycles required before breakage-an approach often termed fatigue testing. The technique provides novel results, which appear to indicate more sizable differences between samples than arise from conventional constant-rate extension experiments. For example, results illustrate a substantially higher tendency for breakage in Afro hair as compared to Caucasian hair-a conclusion that appears in line with consumer experiences. Also, findings suggest a substantially larger contribution from the relative humidity of the environment to the propensity for breakage under these conditions.The fatigue approach also lends itself to a novel means of data analysis in which breakage is treated as a statistical variable rather than as a mechanical parameter. By performing Weibull analysis of the data, a characteristic lifetime and a shape parameter are obtained to characterize the data, while survival probability plots can be generated to predict the propensity for breakage under a specific set of conditions.