Mechanism of wood rupture under compression and shear.

摘要

The main objective of this work is to conduct some basic research on the mechanism of wood rupture under compression and shear forces, especially on how and to what extent wood fiber is modified by compression. More precisely, this work intends to examine the characteristics of structural failures of wood under various conditions such as mechanical stress, compression strain, moisture content, temperature and chemical treatments. With this understanding, we might be able to find an energy-efficient way to, achieve a fiber separation and an internal delamination, and finally achieve an energy saving and pulp quality improvement.; In the first series of experiments, the effect of temperature on the rupture behaviors of wood in the radial, tangential and longitudinal compressions is examined. The results indicate that wood responses similarly in both the radial and tangential compressions at various temperatures, and that fiber collapse in a transverse direction is mainly determined by the tubular structure of fiber.; The effect of sulfonation on the behavior of wood in radial compression is examined in a second series of experiment. In sulfonation, the temperature is by far the most influential factor on the level of sulfonation. The early- and latewood are sulfonated to a similar sulfonate level under the same conditions. The sulfonation decreases the physical properties of wood such as the modulus, specific compression energy, and stresses of both the first and second plastic zones. There exists a linear relationship between these physical properties and the sulfonate content. However, there is no fundamental change in the form of the compression curve at various sulfonate contents.; This study suggests that static compression with large strain (>50%) modifies the wood matrix in two aspects: first, it flattens the fibers, and greatly reduces their transverse resistance. Second, it modifies the fiber's microstructure at different levels, pre-setting a more favorite fiber separation mode and fiber development process, and rendering the wood more suitable for further processing into a mechanical pulp with improved quality. All these may potentially change the refining process from a fatigue process to a more efficient breakdown process, and finally result in an improved pulp quality and a reduced refining energy consumption. (Abstract shortened by UMI.)