3D printed polyurethane exhibits isotropic elastic behavior despite its anisotropic surface

Abstract

<jats:sec> <jats:title content-type="abstract-subheading">Purpose</jats:title> <jats:p>Mechanical properties testing of the hyperelastic thermoplastic polyurethane (TPU) produced by the continuous digital light processing (CDLP) method of additive manufacturing. Primarily, this paper aims to verify that 3D printed TPU still satisfies commonly assumed volumetric incompressibility and material isotropy in elastic range. The secondary aim is to investigate the accuracy and reproducibility of the CDLP method.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Design/methodology/approach</jats:title> <jats:p>Cylindrical samples were printed and subjected to a volumetric compression test to reveal their bulk modulus K and maximal theoretical porosity (MTP). Dog bone specimens were oriented along different axes and printed. Their dimensions were measured, and they were subjected to cyclic uniaxial tests up to 100% strain to reveal the level of stress softening and possible anisotropy. The hyperelastic Yeoh model was fitted to the mean response.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Findings</jats:title> <jats:p>The authors measured the bulk modulus of K = 1851 ± 184 MPa. The mean MTP was 0.9 ± 0.5%. The mean response was identical in both directions and the data could be fitted by the isotropic third order Yeoh function with R^2 = 0.996. The dimensions measurement revealed the largest error (above 5%) in the direction perpendicular to the direction of the digital light projection while the dimensions in other two dimensions were much more accurate (0.75 and 1%, respectively).</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Practical implications</jats:title> <jats:p>The TPU printed by CDLP can be considered and modelled as isotropic and practically volumetrically incompressible. The parts in the printing chamber should be positioned in a way that the important dimensions are not parallel to the direction of the digital light projection.</jats:p> </jats:sec> <jats:sec> <jats:title content-type="abstract-subheading">Originality/value</jats:title> <jats:p>The authors experimentally confirmed the volumetric incompressibility and mechanical isotropy of the TPU printed using the CDLP method.</jats:p> </jats:sec>

Thermoplastic polyurethane for three‐dimensional printing applications: A review

“…Only when the air gap was sufficiently big did the raster pattern become noticeable. The maximal stress was determined to be independent of temperature within 190–205°C 48 . Also, Nectarios Vidakis studied the effect of layer height and nozzle temperature.…”

“…The extrusion parameters, such as the extruder temperature and the print speed, can be adjusted to control the porosity of the final structure. For example, printing at a lower temperature or reducing the print speed can result in a more porous structure 48,71 …”

“…For example, printing at a lower temperature or reducing the print speed can result in a more porous structure. 48,71 3.5.3 | Using a sacrificial material A sacrificial material can be used to create porous structures. A second material, such as a water-soluble material, is printed alongside the main material.…”

“…Only when the air gap was sufficiently big did the raster pattern become noticeable. The maximal stress was determined to be independent of temperature within 190-205 C 48.…”

FDM Layering Deposition Effects on Mechanical Response of TPU Lattice Structures

“…Due to this principle of deposition of the material, this technology presents some pitfalls. In fact, by building FDM parts from bottom to top, the material in the current layer solidifies before the next one is placed on it [ 4 ], causing incomplete interlayer adhesion and often leaving voids in solidified structure, resulting in a decrease in mechanical performance [ 5 ]. In addition to this, a combination of several parameters such as raster orientation, air gap, bead width, color, model temperature, infill, etc.…”