Advanced optical methods for whole field displacement and strain measurement

Measuring deformation and strain in materials and structures provides important information for designing and dimensioning products as well as providing a scientific basis for optimization, quality control and assurance. Digital Speckle Pattern Interferometry (DSPI) and Digital Image Correlation (DIC) are two typical whole-field, non-contact experimental techniques that allow rapid and highly accurate measurement of 3D-deformation and strain distributions with high resolution. The former can measure small deformation (in nanometric level) and can thus determine small strain (in micro strain level), the latter can measure relatively large deformation (micrometer and larger) and can thus determine large strain (from hundreds of micro-strain to considerable value). The combination of these two techniques covers from small to large ranges for whole field, noncontacting deformation and strain measurement, e.g. from nanometric level to a few millimeters or larger for deformation measurement and from micro strain to a few percents or larger for strain measurement. This paper reviews ESPI and DIC and their applications. Both potentials and limitation are listed. The challenges of these two techniques for real world applications are presented and analyzed. The novel developments and optimizations for practical application are presented or demonstrated.