Analysis of Strain Distribution of Softwood in Transverse Compression Measured by Digital Image Correlation Method
Koji MURATA and Minoru MASUDA
Abstract:Strain distributions on a cross section of softwood under transverse compression were analyzed in detail using digital image correlation method. We discussed the relationship between compression strain distributions in an annual ring and anatomical structure (earlywood and latewood). In radial compression, local large shear strains were observed in the edge of earlywood near annual ring boundary where mechanical properties change abruptly along radial direction. In a plastic region of stress-strain curve we found a row of large compression strain that is thought to be cell-wall collapse in earlywood. A start point of the row of large compression strain was the edge of earlywood in which the large shear strain were observed, because the radial wall of sheared cell are easily buckled. In the case of 45 degree compression, large compression strain along loading direction was observed in earlywood. Large expansion strain across the loading direction was also observed in the same area because of Poisson's ratio effect. As the strains were transformed to radial-tangential coordinate system, large shear strain and little normal strain were observed in early wood. The shear strain under 45 degree compression was larger than that under radial compression. The former is the shear strain that is usually called rolling shear. Key Words:Strain distribution, Transverse compression, Earlywood and latewood, Shear strain, Digital image correlation method