We have been proposed a phase shifting speckle shearing interferometer using a diffraction grating for measuring the strain distribution. A strain is obtained by the spatial differentiation of the in-plane component of the deformation. In this system, to measure the in-plane component of the object deformation, the object surface is illuminated in two symmetrical directions about the normal of the object surface. Moreover, the spatial differentiation of the in-plane deformation and phase-shifting are achieved by the diffraction grating. However, the object surface is illuminated by a He-Ne laser in the conventional method, and the illuminating direction is changed by switching the optical path mechanically. Then, we use laser diodes as a light source which has high power and is small size. But, coherency of laser diode is low. In this method, as common path arrangements are used, the path difference is so small that sheared speckles interfere each other. Therefore, the laser diode can be applicable for this measuring system. Additionally, in order to illuminate the object from two directions, two independent laser diodes are used. So, the optical path change is performed electrically. The strain distribution of the bending cantilever is measured with this two laser diodes method. The measured result coincides with theoretical value qualitatively. Therefore the experimental results show the validity of this method.

Date Published: 4 March 2015
PDF: 7 pages
Proc. SPIE 9302, International Conference on Experimental Mechanics 2014, 93020D (4 March 2015); doi: 10.1117/12.2077039

Published in SPIE Proceedings Vol. 9302:
International Conference on Experimental Mechanics 2014
Chenggen Quan; Kemao Qian; Anand Asundi; Fook Siong Chau, Editor(s)