Electronic speckle photography
H. Alarcon, V. Apablaza, F. Melo
The electronic speckle photography technique allows the determination of very small strain fields directly from the pictures of non deformed and deformed states avoiding the numerical differentiation commonly used in older techniques. This technique is based on the cross-correlation of the pre and post deformed pictures of a surface illuminated by laser, where the interference pattern generated by the rough surface can be utilized as random markers able to track small deformations on the surface [1]. Its non invasive character and high sensitivity make of the electronic speckle photography a very useful tool in the study of material with large Young’s modulus, like the bioceramics. The video of Fig. 1 shows the speckle pattern of a thin flat plastic sample while it is deformed in the plane stress regime.
Mov. 1.- Speckle pattern.
Applying the electronic speckle photography to this sequence of pictures, the strain field is obtained, see Fig. 2. It is worthy to note, the strain field determined with this technique is in good agreement with analytical results for an elastic sample.
Fig. 1.- Strain fields component of a plastic sample with a deformation in the spot F sheer to the frontal face. (left) exx, (right) exy
[1] Ichirou Yamaguchi, Seokho Noh, Koichi Kobayashi and Tamiki Takemori, “Deformation measurement by speckle correlation”, RIKEN Review No. 1 April (1993).