Chapter 8 259 Under these conditions, it is calculated that a 1 μm change in diameter from 65 μm to 66 μm will prolong failure by around 2,000 cycles, while increasing from 84 μm to 85μm is predicted to raise the cycles-to-fail by almost 90,000. Figure 5 extrapolates this process to show breakage predictions as a function of both the applied force and the fiber dimensions. From these plots, it begins to become evident how data from these fatiguing experiments can be used to model fiber breakage and understand the contributions from different variables. Again it is emphasized that we do not know where real-life conditions fall but the above results clearly point to the very strong contribution from the magnitude of the repeating forces (i.e. grooming forces), while also illustrating how those with fine hair are predisposed to a higher tendency for breakage. African vs. Caucasian hair: It is widely recognized that African or Afro hair is considerably more prone to breakage than Caucasian hair, which subsequently leads to very different habits and practices Figure 4. Average cycles-to-fail for Caucasian hair of differing dimensions upon repeated application of a 40 g load at 60% RH