Chapter 8 279 instinctive that mechanisms may change with the presence of increasing stresses leading to experiments crossing over into the non-linear region. This presumption still needs to be investigated. Figure 19. Weibull shape parameters for Caucasian hair as function of repeating stress and RH Figure 20. Survival Probability plots for Caucasian hair at 60% and 90% RH upon repeated application of a 0.010-0.011 g/um2 stress