where ร is the density function of the distribution of stresses ร due to source ร and ร is the cumulated distribution of the effects due to source ร. A graphical interpretation of ร is shown in Figure 8.6.
The possibility of assessment of ร and ร values is very limited and usually they must be determined in arbitrary way, but for certain cases their evaluation is possible. For example, this is the case for equipment damage due to overvoltages. Knowing the