Development of a versatile speckle pattern of nano-sized polymer particles for high-resolution SEM-DIC

Digital image correlation (DIC) in combination with Scanning Electron Microscopy (SEM) and in-situ mechanical testing has great potential to study the micro-mechanical behavior of materials. Yet, the application of a highquality speckle pattern for DIC remains challenging at this scale. Here, we present a versatile polymer particle-based speckle pattern with adjustable speckle size (0.17-1.04 & mu;m) to cover a wide range of magnifications (500x to 5000x) in SEM. This speckle does not completely cover the surface, ensuring the visibility of deformations taking place in the studied object. The quality of the pattern is analyzed to determine the precision, noise, and correctness of the results obtained by SEM-DIC. Out-of-plane displacements are also considered. Depending on the choice of speckle size and imaging parameters, high quality SEM-DIC patterns were obtained. The measurable strain with this method ranges between 0.05% up to 100%. To illustrate the versatility of the speckling method, three different micromechanical test cases on polymer materials are presented. These showed that global and local deformation can clearly be visualized at different magnifications.