Short-Term Creep as Related to Cell-Wall Crystallinity
Abstract
X-ray diffraction technique was utilized to determine the relative degree of crystallinity of some coniferous wood tissues, namely Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) normal and compression wood, and normal wood of Sitka spruce (Picea sitchensis (Bong.) Carr.) and western hemlock (Tsuga heterophylla (Raf.) Sarg.). Total creep values were available from a previous study for test samples matched with those used for determining degree of crystallinity. Creep response was measured using two constant loads corresponding to predetermined initial strain levels of 3,000 (A) and 6,000 (B) μinches/inch.
The relative degrce of cell-wall crystallinity was found to be linearly correlated (inversely) with short-term creep. Results of this investigation also revealed that cell-wall crystallinity contributes up to 67.2 and 51.8% of the total variability in creep response for samples tested at constant loads corresponding to strain levels (A) and (B), respectively. It is suggested that a relatively high degree of crystallinity increases the rigidity of cell wall, which thereby resists excessive creep deformation.
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