Highlights  Modeling of mechanical behavior for the material-jet printed polymers  Validation of the material models by comparing the finite element analysis and physical tensile test with multi-material printed specimens  The result proves that it is possible to create a desired strain field by locally changing the ratio of the digital materials without changing the overall shape

Growth of printed electronics has increased the interest in the nanoparticle inks. Research on flexible electronics has expanded not only due to inherent benefits of producing flexible products but also for its high-throughput manufacturability, such as roll-to-toll (R2R) process. Conventional sintering methods cause microcracks and voids in the sintered nanoink film, which lead to subpar performance, and are not suitable for the high-throughput R2R production. Furthermore, these methods are incompatible with many polymer substrates used in flexible electronics due to their low thermal budget. In this study, we present an alternative method utilizing an intense pulsed light (IPL) with a xenon flash lamp to sinter silver nanoink on a polymer substrate. The IPL method is capable of selectively sintering the silver nanoink in milliseconds without damaging the polymer substrates. The silver nanoink was stencil printed on a polydimethylsiloxane (PDMS) specimen. Samples were prepared using five different sintering conditions and tested under uniaxial strain. Three IPL sintering conditions were compared against a non-sintered (NS) and an oven-sintered (OS) conditions. The IPL-sintered samples show a significant improvement in tensile test over NS and OS samples. Samples sintered at 20 J/cm 2 of flash energy density and 10 ms of duration were stretched up to 27% strain before losing electrical conductivity. Scanning electron microscopy (SEM) confirms these results showing a reduction in porosity of the sintered nanoink as compared to NS and OS samples.

There are urgent needs to characterize and model the mechanical property of additively manufactured composite materials, known as the digital materials, for the computational design and simulation. In this study, most utilized digital material samples, which are the mixture of base polymers, Tango Black+ and Vero White+, by PolyJet (Stratasys) are chosen. Four polynomial models (Neo Hookean model, and two-, three-, and five-parameter Mooney–Rivlin models) are used to fit mechanical tensile test results up to 30% of strain. The material models were adopted in the finite element analysis simulating the tensile test to validate their accuracy. The simulation results based on the two-parameter Mooney–Rivlin model predict the stress at 30% strain with small errors (8.2, 10.5, 0.9, 5.0, and 8.0 for Tango Black+, DM40, DM50, DM60, and DM70, respectively). Additionally, scanning electron microscopy was utilized to analyze the fracture surface of the base materials (Tango Black+ and Vero White+) and the digital materials.

In this study, the mechanical properties, in terms of stress-strain curves, of additively manufactured polymeric composite materials, Tango Black Plus (TB+), Vero White Plus (VW+), and their intermediate materials with different mixing ratios, are reported. The ultimate tensile strength and elongation at break are experimentally measured using ASTM standard tensile test. As the content of VM+ increases, the strength of the polymeric materials increases and elongation decreases. Additionally, the Shore A hardness of the materials increases with reduced TB+ concentration. In parallel to the experiment, hyperelastic models are employed to fit the experimental stress-strain curves. The shear modulus of the materials is obtained from the Arruda-Boyce model, and it increases with reduced concentration of TB+. Due to the good quality of the fitted data, it is suggested that the Arruda-Boyce model is the best model for modeling the additively manufactured polymeric materials. With the well characterized and modeled mechanical properties of these hyperelastic materials, designers can conduct computational study for application in flexible electronics field.