The continuous stiffness measurement (CSM) method was used to study the viscoelastic properties of Scots pine (Pinus sylvestris L.) wood, their dependence on the frequency and amplitude of probing oscillations, and wood hardness at different scale levels directly in situ during nanoindentation. The contribution of different frequencies and amplitudes of harmonic oscillations to the formation of the total viscoelastic response of pine wood was determined, and the effect of an additional oscillating load on its dynamic parameters was estimated. It was found that there is a clear division into earlywood and latewood according to hardness and dynamic elasticity (storage) and loss (dissipation) moduli. It was shown that when indentation occurs directly into the cell wall, the hardness has a maximum value for both earlywood and latewood. With an increase in the deformation zone size to 4.5 μm, all dynamic indicators reach a plateau and remain virtually unchanged up to the ultimate depths hmax for both states of wood. Possible mechanisms for such behavior of CSM dynamic parameters are discussed.
Tyurin et al. (Mon,) studied this question.