Repetitive impact loading causes local plastic deformation in wood

The relationship between the impactor velocity and the amount of strain localization in a single impact compression of cellular solids is known. However, few studies report on the effects of repeated high frequency compression. We therefore studied the mechanical behavior of Norway spruce, a cellular viscoelastic material, before, during, and after cyclic high frequency, high strain rate, compression. A custom made device applied 5000-20 000 unipolar (constrained compression and free relaxation) fatigue cycles with a 0.75 mm peak-to-peak amplitude at 500 Hz frequency. The consequences of this treatment were quantified by pitch-catch ultrasonic measurements and by dynamic material testing using an encapsulated Split-Hopkinson device that incorporated a high-speed camera. The ultrasonic measurements quantified a stiffness modulus drop and revealed the presence of a fatigued low modulus layer near the impacting surface. Such a localized plastic deformation is not predicted by classical mechanics. We introduc...

[1]  G. Gray,et al.  Compressive Properties of a Closed‐Cell Aluminum Foam as a Function of Strain Rate and Temperature , 2002 .

[2]  John W. Gillespie,et al.  Dynamics of metal foam deformation during Taylor cylinder–Hopkinson bar impact experiment , 2003 .

[3]  Michael F. Ashby,et al.  On the mechanics of balsa and other woods , 1982, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[4]  N. Fleck,et al.  Compression fatigue of a cellular Al alloy , 1999 .

[5]  Chwee Teck Lim,et al.  Plastic deformation modes in rigid polyurethane foam under static loading , 2001 .

[6]  E. Hæggström,et al.  Quantifying fatigue generated in high strain rate cyclic loading of Norway spruce , 2009 .

[7]  V.P.W. Shim,et al.  An analysis of stress uniformity in split Hopkinson bar test specimens , 2005 .

[8]  L. Benabou.  Predictions of compressive strength and kink band orientation for wood species , 2010 .

[9]  Michael D. Gilchrist,et al.  Designing the energy absorption capacity of functionally graded foam materials , 2009 .

[10]  V.P.W. Shim,et al.  Lateral crushing in tightly packed arrays of thin-walled metal tubes , 1986 .

[11]  Evangelos J. Biblis,et al.  Transitional variation and relationships among properties within loblolly pine growth rings , 1969, Wood Science and Technology.

[12]  V. Placet,et al.  Viscoelastic properties of green wood across the grain measured by harmonic tests in the range 0–95°C: Hardwood vs. softwood and normal wood vs. reaction wood , 2007, 0906.3614.

[13]  J. Banhart,et al.  Strain hardening during constrained deformation of metal foams - Effect of shear displacement , 2009 .

[14]  Q.M. Li,et al.  Degradation of Elastic Modulus of Progressively Crushable Foams in Uniaxial Compression , 2008 .

[15]  D. Mohr,et al.  Nucleation and propagation of plastic collapse bands in aluminum honeycomb , 2003 .

[16]  D. Ouis,et al.  On the frequency dependence of the modulus of elasticity of wood , 2002, Wood Science and Technology.

[17]  M. Fortes,et al.  Characterization of deformation bands in the compression of cellular materials , 1993 .

[18]  Stephen R Reid,et al.  Dynamic uniaxial crushing of wood , 1997 .

[19]  Stephen R Reid,et al.  Inertia effects in uniaxial dynamic compression of a closed cell aluminium alloy foam , 2002 .

[20]  Zhijun Zheng,et al.  Dynamic crushing of 2D cellular structures: A finite element study , 2005 .

[21]  Svante Widehammar,et al.  Stress-strain relationships for spruce wood: Influence of strain rate, moisture content and loading direction , 2004 .

[22]  Mourad Khelifa,et al.  Elasto-plastic constitutive law for wood behaviour under compressive loadings , 2009 .

[23]  Xin-Lin Gao,et al.  Dynamic crushing behavior of honeycomb structures with irregular cell shapes and non-uniform cell wall thickness , 2007 .

[24]  J. Banhart,et al.  Fatigue of a laterally constrained closed cell aluminum foam , 2008 .

[25]  Y. Chui,et al.  Stress-Strain Response of Wood Under Radial Compression. Part I. Test Method and Influences of Cellular Properties , 2000 .

[26]  O. Vitrac,et al.  Assessment of continuous distribution of wood properties from a low number of samples: Application to the variability of modulus of elasticity between trees and within a tree , 2005 .

[27]  M. Ashby,et al.  Fatigue failure of an open cell and a closed cell aluminium alloy foam , 1999 .

[28]  L. Faria,et al.  Material model of metallic cellular solids , 1997 .

[29]  K. Ando,et al.  Mechanism for deformation of wood as a honeycomb structure I: Effect of anatomy on the initial deformation process during radial compression , 1999, Journal of Wood Science.

[30]  Elias Siores,et al.  Compressive behaviour of aluminium foams at low and medium strain rates , 2002 .

[31]  L. Berglund,et al.  Elastic deformation mechanisms of softwoods in radial tension – Cell wall bending or stretching? , 2008 .

[32]  Mccullough,et al.  The stress–life fatigue behaviour of aluminium alloy foams , 2000 .

[33]  J. Sperry,et al.  Water transport in plants obeys Murray's law , 2003, Nature.

[34]  A. Amash,et al.  Study on cellulose and xylan filled polypropylene composites , 1998 .

[35]  Stephen R Reid,et al.  Dynamic crushing of honeycombs and features of shock fronts , 2009 .

[36]  R. F. Ker,et al.  The mechanical properties of the human subcalcaneal fat pad in compression. , 1990, Journal of anatomy.

[37]  Qingming Li,et al.  Strain Measures for Rigid Crushable Foam in Uniaxial Compression , 2002 .

[38]  P. Williams,et al.  Measuring wheat hardness by revolutions per minute reduction , 1987 .

[39]  M. Norimoto,et al.  Influence of Thermal Softening and Degradation on the Radial Compression Behavior of Wet Spruce , 1998 .

[40]  Tongxi Yu,et al.  Collapse of periodic planar lattices under uniaxial compression, part II: Dynamic crushing based on finite element simulation , 2009 .

[41]  Stephen R Reid,et al.  Dynamic compressive strength properties of aluminium foams. Part II—‘shock’ theory and comparison with experimental data and numerical models , 2005 .

[42]  G. Irvine.  The significance of the glass transition of lignin in thermomechanical pulping , 1985, Wood Science and Technology.

[43]  G. Almeida,et al.  Changes in Physical Properties of Yellow Birch Below and Above the Fiber Saturation Point , 2007 .

[44]  R. Laschimke.  Investigation of the wetting behaviour of natural lignin - a contribution to the cohesion theory of water transport in plants , 1989 .

[45]  Stefanie E. Stanzl-Tschegg,et al.  Fracture behaviour of wood and its composites. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture , 2009 .