Application of Laser Speckle Pattern Interferometry for Precise Measurements of Displacement Distribution in Porous Ceramics

This paper deals with experiments for detecting two-dimensional small deformations by laser speckle pattern interferometry system. The optical setup uses a laser diode for the source together with a lens to expand the laser beam, and an inspection area can be chosen with the optical setup between 5 × 7.5 mm2 (microscopic range) up to 200 × 300 mm2 (macroscopic range). The measurements by the macroscopic and microscopic ranges are performed without marking to get overall and detailed deformations of porous ceramic materials respectively. In the macroscopic measurement, it was shown that pore of the ceramics is recognized as a kind of the marker in generating interference fringe. On the other hand, displacement behavior related to the microscopic structure of material can be observed when spatial decomposition of measuring distance is smaller than the pore size is achieved by limiting the inspection area to micro region. In this condition, displacement data with continuous distribution has not been obtained, because displacement measured at pore inside and that at material surface are detected in the one under way without distinguishing at all in the measurement for this microscopic region. However, through the measurement of displacement behavior in crack tip vicinity, it was confirmed that measured displacement distribution agrees with the analytic solution if the data is detected in the position where pore and surface concavity are avoided along the crack edge. By arranging measured data based on above-mentioned processing, valuable information such as strain distributions between adjacent pore was obtained from the measurement for microscopic region.