48 S.M. Kleinendorst et al. Fig. 8.1 Schematic representation of the mechanical shape correlation (MSC) method to identify model parameters ai from an experiment. Simulations supply the images f to which the experiment is compared The method is demonstrated by means of virtual experiments, dedicated to stretchable electronic interconnects. These interconnects are wire-like structures and hence their outline is large with respect to the volume of the structure. In this case the interconnects are not glued to a stretchable substrate, but they are free-standing and hence free to deform threedimensionally, making it difficult to analyze their mechanical behavior with existing techniques. Therefore, these structures make an interesting test case for the MSC technique. The deformation of the interconnects can globally be split in two main modes: torsion of beams and double (S-shaped) bending of beams. These two modes are treated separately in the virtual experiments in this work. The outline of the paper is as follows. In Sect. 8.2 the MSC algorithm is introduced and compared to the integrated digital image correlation algorithm, highlighting the differences. Next the image type used for Mechanical Shape Correlation, i.e., the specimen projections, are explained and the important steps in the formation of these images are stepped through. In Sect. 8.4 two virtual experiment concerning the main deformation modes in the stretchable electronic interconnect structures are presented. In the last section conclusions are drawn. 8.2 Algorithm The algorithm for Mechanical Shape Correlation is based on Integrated Digital Image Correlation (I-DIC) methods, see e.g. [1]. In I-DIC grayscale images of the sample, containing a speckle pattern, before and after deformation are compared, based on the optical flow relation, which means that material points are assumed to have the same gray value before and
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