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

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 pixels2). 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.

► Sub-pixel interpolation is achieved using phase component.
► Strain maps can be extracted without derivation of a displacement map.
► Small speckles and gray level noise averaging give best results.