Advancements in Fused Filament Fabrication (FFF) have enabled the production of polymers with enhanced properties. However, their complex mechanical behavior, especially under impact, remains difficult to model. This study introduces a constitutive model for FFF-printed Tough PLA that accounts for anisotropy, strain-rate sensitivity, strain softening, and tension–compression asymmetry. Quasi-static and dynamic impact tests were conducted to calibrate and validate the model. A Three-Network Viscoplastic (TNV) framework was developed to capture the material’s viscoelastic, viscoplastic, and hyperelastic responses. The model incorporates two networks based on the Yeoh hyperelastic formulation with a power-law description of elastic and viscoplastic anisotropy, while a third network employs the anisotropic Holzapfel–Gasser–Ogden–Bergstrom (HGOB) model. The TNV model predicted the uniaxial stress–strain response with an average fitting error of 9.91%, successfully capturing the nonlinear response, strain-rate dependence, and strain-softening behavior observed in tensile experiments. In addition, stress relaxation tests revealed a reduction in stress from approximately 20 MPa to 18.7–19.0 MPa, corresponding to a normalized relaxation of about 5–7% across the different printing orientations. Tension–compression asymmetry was also quantified, with minor deviations observed under compressive loading. Overall, the proposed TNV model provides a robust predictive framework for the mechanical response of FFF-printed Tough PLA across loading conditions.
Stepanova et al. (Thu,) studied this question.
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