Scanning nanoindentation as an instrument of studying local mechanical properties distribution in wood and a new technique for dendrochronology

The paper presents the results of scanning of mechanical properties of coniferous (common pine Pinus sylvestris) and deciduous (small-leaved lime Tilia cordata and common oak Quercus robur) trees wood using nanoindentation on crosscut face. Manifold increase in microhardness H and Young’s modulus $E$ has been observed between early and late wood in every annual growth ring. Significant differences in intraring radial dependencies of $H$ and $E$ have been found among studied species. For all studied species the average values of $E$ and $H$ of early wood in each annual ring are found to be independent from ring width, while such dependence for late wood is weak at most. The ring widths measured by nanoindentation coincide with the ones measured by standard optical method within 2–3%. The developed technique and obtained results can be useful 1) to amend the understanding the origins of macromechanical properties of various wood species and their dependence upon microstructural characteristics and growth conditions, 2) to optimize the technologies of growing, reinforcement and subsequent usage of the wood, 3) to develop new independent high resolution methods in dendrochronology.