Speckle Photography For Strain Measurement - A Critical Assessment

Speckle photography is a simple technique for measuring displacement in the plane of a surface, so allowing the strain field to be evaluated in two dimensions. A direct experimental comparison of speckle photography with photoelasticity and with finite element analysis on a notched tensile test specimen showed that serious errors could, however, occur due to local surface tilting and to aberrations of the imaging lens. Methods of minimising these effects and those of the speckle decorrelation that can also take place, are discussed.