New Experimental Technique for Material Instability Study

The paper presents a new method applied to measure displacement fields using probability concept. Based on analysis of digital image sequences, we propose the formulation derived from the information of probability between subsets in the un-deformed image and deformed image. The quantity of this information between two subsets establishes a criterion of their mutual dependence based on the maximum a posteriori (MAP) estimate between them. So the subset in deformed image that maximizes the quantity is the corresponding subset of that in un-deformed image. After get the corresponding subset, we can obtain the integer pixel displacement. And we can get accurate displacement field using sub-pixel technique. In the experiments, the method is validated and the resulting solution can show accuracy to 0.02 pixels. This method was also applied successfully to determine the displacement fields of laminated composites under uniaxial compression. The elastic-plastic mechanical behavior and instability of the composites is studied.