Analysis of multilateral internal deformation in wood utilizing the enhanced digital image correlation technique

The Enhanced Digital Image Correlation (EDIC) technique is an improvement over the DIC technique in that it utilizes low frequency tracking (LFT) algorithm, fast normalized cross-correlation (FCC) algorithm and the concepts of phase correlation, and is therefore very tolerant of illumination changes and low contrast. This technique can produce stable and accurate measurement of deformation, which allows observation of local dimensional changes of a heterogeneous and hygroscopic material like wood. To deal with the large amounts of data from the EDIC technique, several data investigation tools were developed and integrated into the Internal Deformation Analysis System (IDEAS). Utilizing the EDIC technique and the IDEAS, we observed the following phenomena that previously were not possible to detect using conventional shrinkage measurement techniques: (a) the internal deformation process was found to be neither linear nor uniform; (b) local regions above the FSP exhibit shrinkage; (c) rays create the alternating pattern of the greater and lesser tangential drying stresses by interrupting the tangentially transmitted drying stresses in the black cherry sample; (d) positive strain in the region of larger vessels or earlywood bands are the main cause of the anisotropic shrinkage of the samples; (e) a framework was developed and applied to determine local drying stress and strain of wood during drying.; It was found that the rays, the vessel elements, and the earlywood-latewood bands all play a significant role in the shrinkage of wood during drying. Continued application of this approach and techniques should greatly increase our understanding of the anisotropic shrinkage of wood.