Temperature and water content effects on the viscoelastic behavior of Tilia americana (Tiliaceae) sapwood

The effects of temperature and water content on the viscoelasticity of living and dehydrated Tilia americana sapwood were examined using transient creep (time- and load-dependent deformation) tests under sustained bending loads. Creep tests were performed at 21.1degreesC and -20.5degreesC to determine the magnitudes and types of strains in living and dehydrated samples. Temperature had no effect on the creep rate of living sapwood. However, the creep rate of dehydrated samples at -20.5degreesC was significantly faster than that at 21.1degreesC. Regardless of temperature, sapwood had a faster creep rate than dehydrated samples. With small bending loads, the residual strains in sapwood were larger at 21.1degreesC compared to -20.5degreesC. Temperature did not significantly affect the residual strains in dehydrated samples. For small bending loads, frozen sapwood recovered all residual creep strains when thawed. With larger loads, residual and plastic (permanent) strains increased. We speculate that ice formation in cell lumens partially dehydrates (and thus stiffens and strengthens) cell wall materials and prevents cell wall buckling and elastic restoration after unloading. However, when thawed, sapwood can elastically restore its original configuration, provided it is not excessively bent (by ice or snow accumulations) when frozen.