Abstract
A non-invasive and three-dimensional strain field identification method is developed in line with the full-field digital image correlation. Three-dimensional images of a soft body are obtained by a multi-slice X-ray CT for both undeformed and deformed states. We employ B-spline functions as the basis of displacement field whose continuity and locality lead to the mathematical simplicity of strain evaluation and the computational efficiency of identification process. The CT images of biological soft tissues are smooth and speckle-less in general, therefore they often induce an indefiniteness of solution. To guarantee the uniqueness of solution, we impose the incompressibility constraint to the displacement field identification by the penalty function method, and minimize the modified objective function of least-square error by the Levenberg-Marquardt method. The minimization yields continuous and smooth fields of displacement and strain. As an experimental example, a heterogeneous compressive strain field within a rubber specimen with granular inclusions is identified to demonstrate the validity of the proposed method. The precision of the identified displacement field is confirmed by comparing with the result of a simple maker-tracing method.
