Influence of 3D printing process parameters on the anisotropic viscoelastic behavior of thermoplastic polyurethane (TPU)

Additive manufacturing, particularly 3D printing, has revolutionized the creation of complex geometries and expanded the applications of materials, including elastomers. Despite these advancements, understanding how 3D printing process parameters affect the anisotropic viscoelastic behavior of 3D-printed elastomers remains a critical challenge. This study investigates the mechanical behavior and stress relaxation characteristics of 3D-printed thermoplastic polyurethane (TPU) under varying drying conditions, printing temperatures, raster angles, and strain rates. Tensile and relaxation tests reveal a strong strain rate dependency and the critical influence of filament drying on mechanical properties. Specimens dried for 8 hours exhibit higher stress and modulus of elasticity than those dried for 3 hours, highlighting the role of moisture removal in enhancing stiffness. Comparisons between 230°C (8-hour drying) and 250°C (3-hour drying) specimens confirm that extended drying improves mechanical performance more than a change in printing temperature. The anisotropic nature of 3D-printed TPU is evident in raster orientation effects, where 0° raster specimens exhibit superior strength, modulus of elasticity, and large deformation, while 90° raster specimens fail at lower strain values due to weaker interlayer adhesion. Stress relaxation tests further confirm that 0° raster specimens experience higher total and equilibrium stresses, leading to more significant absolute stress decay. These findings provide key insights into optimizing 3D printing parameters to improve the mechanical reliability and long-term performance of TPU components in engineering applications.