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Abstract
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.
Highlights
Surface densification of wood increases the hardness and wear resistance of the surface for use in products such as flooring and table tops, where the surface is of primary interest
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 indentationversus-time curve and the density profile
Over the course of a complete hardness test an increasing volume of wood is stressed by the applied force and the slope of the indentation-versustime curve changes depending on the change in test force and on the change in density and volume of the stressed wood
Summary
Surface densification of wood increases the hardness and wear resistance of the surface for use in products such as flooring and table tops, where the surface is of primary interest. The DP has a large influence on the measured hardness (Laine et al 2013). Part 1 of this study (Scharf et al 2022) showed that even though hardness is a commonly measured property of surface-densified wood, it should not be used as a material property, as the obtained hardness values are strongly dependent on test parameters and test material homogeneity (Rautkari et al 2011). It is proposed that the DP itself can be used as the true indicator of the material properties. A hardness number acquired according to standardised test methods represents only the final moments of the hardness test, neglecting the previous response of the material to the test load. Two specimens, exhibiting the same hardness, may show a different indentation-versustime curve, yet exhibit the same hardness value (Figure 1)
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