Strain field measurement by transverse digital holography

The technique generally referred to as speckle correlation interferometry may be described as transverse digital holography when phase stepping is applied, because phase stepping allows complete maps to be obtained of the transverse displacement of an object surface. This paper describes the analysis of these maps to obtain surface strain by fitting data to flat surfaces for least square error within sections of the map. Examples are shown for measuring rotation, thermal contraction, and strains around the tip of a notch. Only uniaxial strain is measured; however, the possibility for biaxial measurement is considered.