Damage evolution in wood: synchrotron radiation micro-computed tomography (SRμCT) as a complementary tool for interpreting acoustic emission (AE) behavior

Abstract Tensile tests of miniature spruce wood specimens have been performed to investigate the damage evolution in wood at the microscopic scale. For this purpose, the samples were stepwise tensile loaded in the longitudinal (L) and radial (R) directions and the damage evolution was monitored in real-time by acoustic emission (AE) and synchrotron radiation micro-computed tomography (SRμCT). This combination is of outstanding benefit as SRμCT monitoring provides an insight on the crack evolution and the final fracture at microscopic scale, whereas AE permits the detection of the associated accumulation and interaction of single damage events on all length scales with high time resolution. A significant drawback of the AE testing of wood has been overcome by means of calibrating the AE amplitudes with the underlying crack length development. Thus, a setup-dependent and wood species-dependent calibration value was estimated, which associates 1 μm2 crack area generating of 0.0038 mV in the detected AE amplitude. Furthermore, for both L and R specimens, AE signals were classified into two clusters by using a frequency-based approach of unsupervised pattern recognition. The shares of AE signals of both clusters correlate with the ratio of the relative crack area of the interwall and transwall cracks gained from the fractographic analysis of SRμCT scans.

[1]  Thierry Chotard,et al.  Characterisation of early stage calcium aluminate cement hydration by combination of non-destructive techniques: acoustic emission and X-ray tomography , 2003 .

[2]  S. Horn,et al.  Quantification of failure mechanisms in mode-I loading of fiber reinforced plastics utilizing acoustic emission analysis , 2012 .

[3]  M Stampanoni,et al.  3D imaging of microstructure of spruce wood. , 2007, Journal of structural biology.

[4]  W. Cousins.  Young's modulus of hemicellulose as related to moisture content , 1978, Wood Science and Technology.

[5]  Andreas J. Brunner,et al.  Damage evolution in wood – pattern recognition based on acoustic emission (AE) frequency spectra , 2015 .

[6]  Wolfgang Ludwig,et al.  Fast X-ray tomography and acoustic emission study of damage in metals during continuous tensile tests , 2007 .

[7]  M. G. R. Sause,et al.  Pattern recognition approach to identify natural clusters of acoustic emission signals , 2012, Pattern Recognit. Lett..

[8]  P. Wyss,et al.  3D micro-scale deformations of wood in bending: synchrotron radiation muCT data analyzed with digital volume correlation. , 2008, Journal of structural biology.

[9]  Simon Henein,et al.  TOMCAT: A beamline for TOmographic Microscopy and Coherent rAdiology experimenTs , 2007 .

[10]  F. Darwish,et al.  Detection of fiber cracking by acoustic emission. , 1972 .

[11]  J. C. Radon,et al.  Acoustic emissions and energy transfer during crack propagation , 1972 .

[12]  Dominique Derome,et al.  Hysteretic swelling of wood at cellular scale probed by phase-contrast X-ray tomography. , 2011, Journal of structural biology.

[13]  S. Stanzl-Tschegg,et al.  Detection of the Fracture Path under Tensile Loads through in situ Tests in an ESEM Chamber , 2003 .

[14]  I. Burgert,et al.  The radial reinforcement of the wood structure and its implication on mechanical and fracture mechanical properties—A comparison between two tree species , 2002 .

[15]  Michael F. Ashby,et al.  The fracture and toughness of woods , 1985, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[16]  Gilles Peix,et al.  Damage Evolution Analysis in Mortar, During Compressive Loading Using Acoustic Emission and X-ray Tomography: Effects of the Sand/Cement Ratio , 2007 .

[17]  Rey Ramírez,et al.  Source localization , 2008, Scholarpedia.

[18]  M. Friswell,et al.  Ultrastructural mechanisms of deformation and failure in wood under tension , 2013 .

[19]  Marc Stevens,et al.  X-ray tomography as a tool for detailed anatomical analysis , 2009, Annals of Forest Science.

[20]  Marco Stampanoni,et al.  Synchrotron-based tomographic microscopy (SbTM) of wood: development of a testing device and observation of plastic deformation of uniaxially compressed Norway spruce samples , 2012 .

[21]  Veerle Cnudde,et al.  Use of X-ray computed microtomography for non-invasive determination of wood anatomical characteristics. , 2004, Journal of structural biology.

[22]  I. Burgert,et al.  A close-up view of wood structure and properties across a growth ring of Norway spruce (Picea abies [L] Karst.) , 2009, Trees.

[23]  R. Abela,et al.  Trends in synchrotron-based tomographic imaging: the SLS experience , 2006, SPIE Optics + Photonics.

[24]  S. Wilkins,et al.  Simultaneous phase and amplitude extraction from a single defocused image of a homogeneous object , 2002, Journal of microscopy.

[25]  M. Lysak.  Development of the theory of acoustic emission by propagating cracks in terms of fracture mechanics , 1996 .