Strain Measurement in Wood using A Digital Image Correlation Technique


  • Audrey G. Zink
  • Robert W. Davidson
  • Robert B. Hanna


Strain measurement, image analysis, mechanical testing


The suitability of the Digital Image Correlation Technique (DICT) for full-size test specimens of wood and wood-based composites was evaluated in this study. The technique utilizes pairs of digitized video images of undeformed and deformed test specimens and an image correlation computer routine to measure the displacements of any or all points on the surface of the test specimen. New methods for image acquisition and image correlation were developed and evaluated in this study.

Evaluation and calibration were performed using an aluminum alloy block for comparison and axial compression of small, clear specimens of wood and in accordance with ASTM D143-83 (1986a). Comparison of strain measurements obtained using an independent measurement technique and strain obtained with the DICT showed close agreement. Utilizing DICT for full-field strain distributions through an increasing load series revealed progressive failure development in the wood specimens, the eventual failure mode, and a shift in strain concentrations during load application.


ASTM. 1986a. Standard methods of testing small clear specimens of timber. Standard D143-83. American Society for Testing and Materials, Philadelphia, PA.nASTM. 1986b. Ovendry method. Standard D2016-83, Method A. American Society for Testing and Materials, Philadelphia, PA.nChoi, D. 1990. Failure initiation and propagation in wood in relation to its structure. Ph.D. dissertation, State University of New York, Syracuse, NY.nChoi, D., J. L. Thorpe, and R. B. Hanna. 1991. Image analysis to measure strain in wood and paper. Wood Sci. Technol. 25:251-262.nChu, T. C. 1982. Digital image correlation method in experimental mechanics. Ph.D. dissertation, University of South Carolina, Columbia, SC.nHe, Z. H., M. A. Sutton, W. R. Ranson, and W. H. Peters. 1984. Two-dimensional fluid-velocity measurements by use of digital speckle correlation techniques. Exp. Mech. 24(2): 117-121.nHolman, J. P. 1984. Experimental methods for engineers. 4th ed. McGraw-Hill Book Co., New York, NY.nLukasiewicz, S. A., M. Stanuszek, and J. A. Czyz. 1993. Filtering of the experimental data in plane stress and strain fields. Exp. Mech. 33(2): 139-147.nLuo, P. F., Y. J. Chao, and M. A. Sutton. 1994. Experimental evaluation of J-integral using both in-plane deformations and caustics obtained from out-of-plane displacements. Pages 248-253 in Proc. 1994 SEM Spring Conference on Experimental Mechanics, June 1994, Baltimore, MD.nPeters, W. H., and W. F. Ranson. 1982. Digital imaging techniques in experimental stress analysis. Optical Eng. 21(3):427-431.nRanson, W. F., D. M. Waler, and J. B. Caulfield. 1986. Biomechanics in Computer vision in engineering mechanics, a discussion paper for the NSF Workshop on Solid Mechanics Related to Paper, August, 1986, Blue Mountain Lake, New York.nSutton, M. A., W. J. Wolters, W. H. Peters, W. F. Ranson, and S. R. McNeill. 1983. Determination of displacements using an improved digital correlation method. Image Vision Comput. 1(3): 133-139.nSutton, M. A., T. L. Chae, J. L. Turner, and H. A. Bruck. 1990. Development of a computer vision methodology for the analysis of surface deformations in magnified images. ASTM STP 1094, MiCon 90, 109-132. American Society for Testing and Materials, Philadelphia, PA.nSutton, M. A., J. L. Turner, H. A. Bruck, and T. A. Chae. 1991. Full-field representation of discretely sampled surface deformation for displacement and strain analysis. Exp. Mech. 31(2):168-177.nVendroux, G. 1994. Scanning tunneling microscopy in micromechanics investigations. Ph.D. thesis, California Institute of Technology, Pasadena, CA.nZink, A. G. 1992. The influence of overlap length on the stress distribution and strength of a bonded wood double lap joint. Ph.D. dissertation, SUNY-CESF, Syracuse, NY.n






Research Contributions