Hardness of surface-densified wood. Part 2: Prediction of the density profile by hardness measurements

Abstract

The density profile of surface-densified wood has a major influence on the indentation resistance of the material. A method that can predict the density profile in surface-densified wood from measurements of the indentation in a hardness test was established. The combined information of hardness and density profile is expected to better assess the performance of surface-densified wood. Density profile and hardness test data for surface-densified Scots pine have been subjected to a partial least squares analysis to determine the relationship between the indentation depth measured during a hardness test and the density profile measured by X-ray densitometry. Among seven different hardness tests, which varied in test force and indenter geometry, the Brinell method according to the EN 1534 standard showed the highest correlation between the indentation-versus-time curve and the density profile. The mean absolute error for the prediction of density profiles in an external test set was 5-10%, indicating that the method proposed in this study can be used to replace X-ray densitometry in process control and process design.