Thermoviscoelasticity in extrusion deposition additive manufacturing process simulations

The Extrusion Deposition Additive Manufacturing (EDAM) process, more commonly known as Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF), is a promising new manufacturing method for high temperature tooling and molds. However, nowadays this process is still largely empirically calibrated. Based on the required capabilities for determining residual stresses and the final deformation state of printed parts and their effects on the part performance, there is a large interest in the development of process simulations. To this end, a set of simulation tools has been implemented in Abaqus/Standard through a user subroutine suite at Purdue University to model the EDAM process. This work extends these simulation capabilities to include thermoviscoelastic material properties. An incremental linear thermoviscoelastic model is presented for an anisotropic material and implemented in Abaqus with a UMAT user subroutine. The thermoviscoelastic properties of a 50wt.% carbon fiber reinforced Polyphenylene Sulfide (PPS) were characterized in relaxation experiments and the implemented model was verified using the experimental data. To assess the significance of crystallization informed thermoviscoelastic material properties, process simulation results were compared for an autoclave tool. Here, the outcomes of the thermoviscoelastic analysis were compared with a simulation considering temperature dependent elastic properties. The results of this comparison indicate that it is essential to capture viscoelasticity that is informed by crystallization in order to predict realistic stress levels for subsequent performance analyses. In addition to the stresses, the resulting final deformations differ significantly for both analyses as well. The different internal stress levels after deposition and the crystallization informed material stiffness in the thermoviscoelastic analysis are the main causes for this deviation.