MorphFlow: Estimating Motion in In-Situ Tests of Concrete

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Abstract Background In situ Computed Tomography is a valuable tool to investigate failure mechanics of materials in 3D. For brittle materials with sudden fracture like concrete however, state-of-the-art methods such as Digital Volume Correlation fail to produce displacement fields that display the discontinuous behavior of load induced cracking correctly. Objective The main objective is to develop an algorithm that calculates displacement fields for large-scale in situ experiments on concrete. Methods The algorithm presented is based on a 3D Optical Flow method solved by a primal-dual procedure and equipped with a coarse-to-fine scheme based on morphological wavelets. The algorithm is publicly available. Our evaluation focuses on the beneficial use of morphological wavelets over classical ones, and on the ability to produce reliable results with limited data. Applying the primal-dual scheme to in situ tests and using morphological wavelets are novel contributions. Results The results show that our algorithm cannot only cope with large volume images, but also produces discontinuous displacement fields that yield high strain in fractured regions. It does not only perform better than state-of-the-art methods, but also achieves sufficient results on reduced data. The morphological wavelets play a key role in this finding - they even allow to deduce cracks of widths less than a voxel. Conclusion Displacement calculation for in situ tests of brittle materials requires voxel-accurate displacement fields that allow for discontinuities. The presented algorithm fulfills these requirements and therefore is a powerful tool for future understanding of failure mechanics in concrete.