Automated laser extensometer for full-field and local in-plane displacements and strains measurement

The novel type of automated laser full-field extensometer based on grating (moire) interferometry is presented. It is designed for medium size field of view (6 x 4.5 mm(2)). The extensometer is mechanically and virtually (through software). integrated with a standard loading machine. It has possibility to control the load on the base of local on-line strain measurements. It enables the measurements during static, monotonic and cyclic loads and full-field analysis of arbitrary sequence of images. The extensometer gives high contrast and good quality interferograms and is insensitive to vibrations and works with simple, low cost laser diode. The apparatus includes very convenient fringe pattern analysis software with possibilities to design the calculation protocol best fitted to specific measurement tasks. The capabilities of the extensometer are presented on the example of low cyclic fatigue testing of steel specimens with notch.