Design, microstructure and mechanical characterization of Ti6Al4V reinforcing elements for cement composites with fractal architecture

This paper presents a study on the design, and microstructural and mechanical characterization of additively manufactured reinforcing elements for composite materials exhibiting fractal geometry, with a focus on the flexural reinforcement of cement-matrix composites. The examined elements are manufactured via an additive process, electron beam melting, from the Ti6Al4V titanium alloy, using a Koch curve construction ruled by three complexity parameters. Koch fibers and meshes are designed, additively manufactured and experimentally tested, through the use of the proposed fractal design procedure. Laser scanning tests illustrate the correspondence between the CAD objects and the additively manufactured samples. The experimental characterization of the surface properties of the Koch fibers is conducted through optical microscopy and contact angle tests, while their mechanical performance is analyzed through Vickers hardness and bending tests on a fiber-reinforced reinforced mortar. The given mechanical tests highlight that reinforcing fibers with fractal architecture significantly enhance the first crack strength and the residual loading capacity of cement mortar specimens subject to three-point bending tests. This is due to the relevant interlocking mechanisms acting at the interface between the matrix and the ribs of such reinforcing elements, which delay the macroscopic cracking of the mortar.