Comparison of the Viscoelastic Properties and Plasticity of Early and Late Wood of Pine and Spruce by Continuous Stiffness Measurement during Nanoindentation

Using a small oscillating load (continuous stiffness measurement, CSM), in addition to the main quasi-static load, we determine the hardness, Young's modulus, storage and loss moduli, mechanical loss coefficient (tan delta), and the plasticity characteristics in various components of the nanostructure and microstructure of pine (Pinus sylvestris) and spruce (Picea abies) wood. The contribution of structures of different scales to the ratio of the viscoelastic properties of early and late wood in the composition of one annual ring is determined. The plasticity characteristic delta(A) is determined, and the influence of an additional oscillating load on the dynamic parameters of wood is assessed.