Instrumented macrohardness testing of wood

Abstract

This study tested the possibility of determining Brinell hardness of wood by instrumented indentation without visually measuring the diameter of the impression. Hardness of beech wood (Fagus sylvatica) and pine wood (Pinus sylvestris) was determined conventionally and compared with that extracted from the respective depth-sensing data. The standard Oliver–Pharr analysis needs to be adapted to the viscoelastic behaviour of wood by using a linear fit to the high load portion of the unloading curve for the determination of contact stiffness. Surface profiles of the residual impressions recorded with a laser scanning microscope revealed sinking-in around the indenter. Therefore, contact area needs to be calculated on the basis of an empirical area function that relates contact depth extracted from depth-sensing data and the visually determined contact area. The procedure offers a few advantages such as the possibility of extracting an indentation modulus and time saving for large test series.

Keywords

Area function Brinell hardness Instrumented indentation Laser scanning microscopy Macroindentation Oliver–Pharr method Sinking-in Viscoelastic unloading

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