An embedded random speckle technique is used to measure the displacement in the near-crack-tip fields in four-point-bending beams made of transparent materials. Stress intensity factors or strains in the different planes are generated from the displacement measurements. The results are compared with the existing theoretical and numerical solutions.
F. P. Chiang,
"Surface And Interior Crack-Tip Field Measurement By An Embedded Random Speckle Method," Optical Engineering 27(3), 273210 (1 March 1988). https://doi.org/10.1117/12.7977914