Indentation experiments and simulations of nonuniformly photocrosslinked polymers in 3D printed structures

In this paper, the microscale mechanical properties of 3D printed multi-layered polymeric structure were investigated by indentation experiments. The indentation modulus appears to be periodically varied inside the multi-layered structure and the overall stiffness of a structure was highly dependent on its printing condition. To elucidate the evolution of the nonuniform mechanical properties, we develop a thermodynamically consistent model which coupled the photopolymerization kinetics together with the reaction-dependent viscoelastic deformation. A correlation between the periodic mechanical properties and the stepwise photopolymerization 3D processing is investigated through the finite element simulations using the theoretical model. Suggestions on how to increase the printing speed of a structure without undermining its mechanical performance are provided.