The Research Of Development And Application Of Digital Volume Correlation

Full-field deformation/strain measurement is important for experimental mechanics, and digital volume correlation is a true three-dimensional technique for full field measurement. The development, the expansion and the application the digital volume correlation will be studied in this thesis.1) A digital volume correlation algorithm was developed based on Newton-downhill method, least squares method, and tricubic B-spline interpolation. The performance of the algorithm was evaluated with two X-ray CT data of metal foams and the proposed digital volume correlation algorithm has a good performance. In the ideal case without noise, the displacement error is 0.0065 voxel, and it increases to 0.008 voxel with noise, and the strain error increases to 100 με. The error of the digital volume correlation was analyzed by the rigid translation simulation test, and it was found that the error mainly comes from the noise of the image and the interpolation, and the interpolation mainly affect the accuracy and the noise mainly affect the precision.2) On the basis of the proposed digital volume correlation algorithm, two independent ex-situ digital volume correlation methods base on image registration and the additive decompose of displacement gradient were developed. The performances of the two ex-situ digital volume correlation methods are evaluated through numerical tests of translational motion, rotational motion, the coupling of translational motion and rotational motion, and uniaxial compression deformation. The two methods have similar accuracy with the in-situ digital volume correlation under small deformation and small rotational motion. Both methods have its own advantage, the ex-situ digital volume correlation method based on image registration can calculate the large deformation, and the ex-situ digital volume correlation method based on the additive decomposition of the displacement gradient is easier to operate. The two methods complement each other and expand the application of digital volume correlation.3) Metallic foams have attracted scientific and industrial interests due to their excellent multifunctional performances. Via examining internal displacement fields and strain fields at four compression states by means of an ex-situ digital volume correlation method, the evolution of cell-scale deformation of open-cell aluminum foams is studied. Local deformation bands are observed in strain fields in spite of the uniform compression measured by displacement fields. Both the spatial distribution and the frequency distribution of strains show deformation heterogeneity. Moreover the heterogeneity has no correlation with local porosity. The compressive, rotational, and shear deformations always arise simultaneously on cell-scale, suggesting the complex deformation mode. Cell rotation caused by neighbor cells deformation is a main deformation mode to mitigate the strain concentrations.