Implementation of the direct evaluation of strains using a phase analysis code for random patterns

Abstract A new approach for decoding directly strains from surfaces encoded with random patterns has been developed and validated. It is based on phase analysis of small region of interest. Here we adapt to random patterns new concepts proposed by Badulescu (2009) on the grid method. First metrological results are encouraging: resolution is proportional to strain level, being 9% of the nominal value, for a spatial resolution of 9 pixels (ZOI 64×64 pixels 2 ). Random noise has to be carefully controlled. A numerical example shows the relevance of the approach. Then, first application on a carbon fiber reinforced composite is developed. Fabric intertwining is studied using a tensile test. Over-strains are clearly visible, and results connect well with the previous studies.

[1]  Hassan Zahouani,et al.  Frequency-based image analysis of random patterns: an alternative way to classical stereocorrelation , 2010 .

[2]  Karen Triconnet,et al.  Étalonnage transverse d'un objectif de caméra par la méthode de la grille , 2004 .

[3]  Roberto Longo,et al.  A digital image correlation method for fatigue test experiments , 2009 .

[4]  M. Grédiac,et al.  Assessment of Digital Image Correlation Measurement Errors: Methodology and Results , 2009 .

[5]  B. Wattrisse,et al.  Analysis of strain localization during tensile tests by digital image correlation , 2001 .

[6]  M. A. Sutton,et al.  Accurate measurement of three-dimensional deformations in deformable and rigid bodies using computer vision , 1993 .

[7]  Ignace Verpoest,et al.  Full field strain measurements for validation of meso-FE analysis of textile composites , 2008 .

[8]  Stéphane Roux,et al.  Extended digital image correlation with crack shape optimization , 2008 .

[9]  C. Badulescu,et al.  A Procedure for Accurate One-Dimensional Strain Measurement Using the Grid Method , 2009 .

[10]  D. Garcia,et al.  A combined temporal tracking and stereo-correlation technique for accurate measurement of 3D displacements: application to sheet metal forming , 2002 .

[11]  Y Surrel,et al.  Additive noise effect in digital phase detection. , 1997, Applied optics.

[12]  Jung-Ryul Lee,et al.  Digital phase-shifting grating shearography for experimental analysis of fabric composites under tension , 2004 .

[13]  W. F. Ranson,et al.  Determination of displacements using an improved digital correlation method , 1983, Image Vis. Comput..

[14]  Michel Bornert,et al.  Experimental characterization of the local strain field in a heterogeneous elastoplastic material , 1994 .

[15]  Gilbert Tribillon,et al.  Measurement of in-plane displacement fields by a spectral phase algorithm applied to numerical speckle photograph for microtensile tests , 2000 .