Zur Anwendung der logarithmischen Normalverteilung in der Materialprüfung

Application of the logarithmic normal distribution in material testing — Misleading norm statements resulting in faulty analyses.

The application of the logarithmic normal distribution (LND) in material testing is useful in cases of large variation coefficients. The general task is, to gain from a sample an information of the characteristic value of the tested material property. For that in ge neral the one-sided lower tolerance limit is calculated.
German application standards and norms regulate this calculation for the use of the LND not in a correct way — the resulting characteristic values for the regular demanded confidence level of 75 % are too favourable. These calculations do not respect the different distributions with different obliquity of the tested attributes in the sample on one hand and of the mean values of all samples on the other one. This mistake in using the LND is shown in examples. A pragmatic intermediate solution is given, up to the necessary revision in the norms.