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Material extrusion based additive manufacturing is used to make three dimensional parts by means of layer-upon-layer deposition. There is a growing variety of polymers that can be processed with material extrusion. Thermoplastic polyurethanes allow manufacturing flexible parts that can be used in soft robotics, wearables and flexible electronics applications. Moreover, these flexible materials also present a certain degree of viscoelasticity. One of the main drawbacks of material extrusion is that decisions related to specific manufacturing configurations, such as the inner-structure design, shall affect the final mechanical behaviour of the flexible part. In this study, the influence of inner-structure design factors upon the viscoelastic relaxation modulus, E(t), of polyurethane parts is firstly analysed. The obtained results indicate that wall thickness has a higher influence upon E(t) than other inner-design factors. Moreover, an inadequate combination of those factors could reduce E(t) to a small fraction of that expected for an equivalent moulded part. Next, a viscoelastic material model is proposed and implemented using finite element modelling. This model is based on a generalized Maxwell model and contemplates the inner-structure design. The results show the viability of this approach to model the mechanical behaviour of parts manufactured with material extrusion additive manufacturing.

Advances in the electricity industry have led to increasing demands for epoxy/anhydride/silica insulation systems. In this present study, the curing reaction kinetics of two epoxy systems are investigated using non-isothermal differential scanning calorimetry (DSC). Their mixtures were isothermally cured under vacuum at 130 °C for differing lengths of time, and their glass transition temperatures, T g , activation energies, E A , and other parameters were determined by DSC. Interest in such systems centres on their industrial applications, for which reason it was decided to study high silica loadings, cured at 130° C; a curing temperature that was shown to be the most appropriate for these systems in all cases, as it prevented cracks and structural defects in the moulding production processes.