Drying strain behavior of elm earlywood and latewood with digital image correlation method.

The strain variations in Elm earlywood and latewood during drying were studied with digital image correlation method. Also, the moisture contents of different water states were quantified based on time-domain nuclear magnetic resonance technique to reveal the strain-water relationships. Although the shrinkage strains gradually increased with increasing drying time, there was a significant difference in the strain distribution of the earlywood and latewood. Owing to latewood large stress, the earlywood was pulled by it to shrink together, and the earlywood maximum shrinkage appeared in the early/latewood junction, while the maximum shrinkage of latewood happened in its middle part. Wood shrinkage strain increased fast in the early-drying stage, mainly influenced by moisture content variation; in the mid-drying stage, the shrinkage increased slowly due to the synergistic effect of free and bound water migration; in the late-drying stage, the bound water variation led to a mild shrinkage. [ABSTRACT FROM AUTHOR]