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Image Based Local Strain Measurement of Wood

  • C. S. MoilanenEmail author
  • P. Saarenrinne
  • B. A. Engberg
  • T. Björkqvist
Conference paper
Part of the Conference Proceedings of the Society for Experimental Mechanics Series book series (CPSEMS)

Abstract

A new method for local strain measurement of soft materials like wood is proposed. Norway spruce samples were subjected to radial compression in an encapsulated split-Hopkinson device (ESHD). High speed photography was used at two magnifications for image based analysis. The strain estimation was made from high magnification images showing compression on local, fiber level for 1–2 growth rings and from low magnification images showing compression on sample level, for 5–8 growth rings. Strain gauges on the ESHD bars give stress and average strain for comparison. Image analysis based on PIV technique gives local and average strain propagation as a function of time. Wood is an inhomogeneous material and thus, local strain is a more proper measure of the response of the material. The high magnification captures differences between earlywood and latewood while the low magnification gives the strain distribution over the whole sample. Both magnifications are important in order to understand the response of the wood material to the sudden compression. A way to estimate the stress field was developed. The results showed similarity to the strain gauge measurement results.

Keywords

Image based measurement Wood Split-Hopkinson bar Local strain Mechanical pulping 

References

  1. 1.
    Uhmeier A, Salmén L (1996) Influence of strain rate and temperature on the radial compression behavior of wet spruce. J Eng Mater Technol Trans ASME 118(3):289–294CrossRefGoogle Scholar
  2. 2.
    Widehammar S (2004) Stress–strain relationships for spruce wood: influence of strain rate, moisture content and loading direction. Exp Mech 44(1):44–48CrossRefGoogle Scholar
  3. 3.
    Gama BA (2004) Hopkinson bar experimental technique: a critical review. Appl Mech Rev 57(4):223–250CrossRefGoogle Scholar
  4. 4.
    Davies RM (1948) A critical study of the Hopkinson pressure bar. Philos Trans R Soc Lond Sect B 240(821):375–457zbMATHCrossRefGoogle Scholar
  5. 5.
    Kolsky H (1949) An investigation of the mechanical properties of materials at very high rates of loading. Proc Phys Soc Lond Sect B 62(II-B):676–700CrossRefGoogle Scholar
  6. 6.
    Widehammar S (2002) A method for dispersive split Hopkinson pressure bar analysis applied to high strain rate testing of spruce wood. Dissertation, Department of Materials Science, Uppsala UniversityGoogle Scholar
  7. 7.
    Siviour CR (2009) A measurement of wave propagation in the split Hopkinson pressure bar. Meas Sci Technol 20(6):065702CrossRefGoogle Scholar
  8. 8.
    Gilat A, Schmidt T, Walker A (2009) Full field strain measurement in compression and tensile split Hopkinson bar experiments. Exp Mech 49:291–302CrossRefGoogle Scholar
  9. 9.
    Saari V, Björkqvist T, Engberg BA, Saarenrinne P (2009) Strain distribution in annual rings under compression by high speed photography. In: Proceedings of international mechanical pulping conference, 31st May–4th June 2009, Mid-Sweden University, SunsvallGoogle Scholar
  10. 10.
    Allais L, Bornert M, Bretheau T, Caldemaison D (1994) Experimental characterization of the local strain field in a heterogeneous elastoplastic material. Acta Metallurgica Et Materialia 42(11):3865–3880CrossRefGoogle Scholar
  11. 11.
    Sutton M, Orteau J, Schreier H (2009) Image correlation for shape, motion and deformation measurements. Springer, New YorkGoogle Scholar
  12. 12.
    Zink A, Davidson R, Hanna R (1995) Strain measurement in wood using a digital image correlation technique. Wood Fibre Sci 27:346–359Google Scholar
  13. 13.
    Vessby J, Serrano E, Enquist B (2010) Contact-free measurement and numerical and analytical evaluation of the strain distribution in a wood-FRP lap-joint. Mater Struct 43:1085–1095CrossRefGoogle Scholar
  14. 14.
    Valla A, Konnerth D, Keunecke D, Niemz P, Muller U, Gindl W (2011) Comparison of two optical methods for contactless, full field and highly sensitive in-plane deformation measurements using the example of plywood. Wood Sci Technol 45:755–765CrossRefGoogle Scholar
  15. 15.
    Thuvander F, Sjödahl M, Berglund L (2000) Measurement of crack tip strain field in wood using a digital image correlation technique. J Mater Sci 35:755–765Google Scholar
  16. 16.
    Raffel M, Willert CE, Wereley ST, Kompenhans J (2007) Particle image velocimetry, a practical guide, 2nd edn. Springer, Heidelberg/New YorkGoogle Scholar
  17. 17.
    Holmgren S-E, Svensson BA, Grandin PA, Lundberg B (2008) An encapsulated split Hopkinson pressure bar for testing of wood at elevated strain rate, temperature, and pressure. Exp Tech 32(5):44–50CrossRefGoogle Scholar
  18. 18.
    Product-manual for Davis 8.0. LaVision GmbH, Göttingren, Germany (2012)Google Scholar
  19. 19.
    Keunecke D, Sonderegger W, Pereteanu K, Lüthi T, Niemz P (2007) Determination of Young’s shear moduli of common yew and Norway spruce by means of ultrasonic waves. Wood Sci Technol 41:309–327CrossRefGoogle Scholar
  20. 20.
    Kolsky H (1963) Stress waves in solids. Dover Publications, New YorkGoogle Scholar

Copyright information

© The Society for Experimental Mechanics, Inc. 2014

Authors and Affiliations

  • C. S. Moilanen
    • 1
    Email author
  • P. Saarenrinne
    • 1
  • B. A. Engberg
    • 2
  • T. Björkqvist
    • 3
  1. 1.Department of Engineering DesignTampere University of TechnologyTampereFinland
  2. 2.Department of Natural Sciences, Engineering and MathematicsMid Sweden UniversitySundsvallSweden
  3. 3.Department of Automation Science and EngineeringTampere University of TechnologyTampereFinland

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