Use of digital speckle pattern correlation for strain measurements in a CuAlBe shape memory alloy

A Cu–Al 11.2 wt.%-Be 0.6 wt.% shape memory alloy was subjected to a uniaxial tension test using an MTS load frame with an attached optical microscope. Digital images of the sample's surface were acquired using white light and He–Ne laser illumination. The obtained images were associated to the engineering stress–strain behavior, which was calculated from the measured displacement, strain and force. From the images, displacement vector fields were calculated for white light and laser illumination by digital image correlation (DIC) and digital speckle pattern correlation (DSPC) techniques respectively. Using white light it was possible to observe the grains and the martensitic phase transformation of the material more clearly than using DSPC; nevertheless, better quantitative results of displacement, in-plane strain and elastic moduli were obtained using DSPC than using DIC when they were compared to the reference values measured by electrical extensometry. Furthermore DIC and DSPC work as complementary techniques to determined the micro and macromechanical behavior of the CuAlBe shape memory alloy.