The quantification of debonding was performed for additively manufactured "fractal" fibers embedded within two brittle matrices. Three pull-out tests were carried out inside of an X-ray tomograph allowing for Digital Volume Correlation analyses. Relative motions at the interfaces were measured thanks to adapted meshes with split nodes. Profiles of normal, tangential and vertical displacement jumps as well as vertical strains in the fibers were used to study interfacial debonding. An articulated load transfer mechanism between the fiber and the matrix was observed in the examined tests, as demonstrated by zigzagged distributions of vertical displacement jumps and vertical strain profiles in the fibers at the initial stages of pull-out. Vertical strain concentrations were observed in correspondence to lateral protrusions (or ribs) of the reinforcing fibers. These results suggest that fiber-matrix interlocking may be affected by geometry-driven tensile stiffening effects between the ribs. For larger values of pull-out displacements, more diffuse damage of the fiber-matrix interface was observed between the ribs, especially in plaster matrices.