OPTICAL METHOD FOR MEASURING POISSON'S RATIO

An accurate, low-cost, non-contact strain measuring method and apparatus for measuring strain in low modulus porous materials using optical microscopy are described wherein, in a preferred embodiment of the invention, fluorescent ink reference lines are applied to a surface of a specimen, the specimen is mounted on the stage of an optical microscope having an attached x-y digital micrometer, and a load is applied to the specimen. The surface is viewed using a light source that renders the reference lines visible, and changes in displacement of selected points on the reference lines are measured for each incremental loading. Poisson's ratio may be calculated from the strain measurements in two orthogonal directions.