Time-Dependent Mechanical Properties in Polyetherimide 3D-Printed Parts Are Dictated by Isotropic Performance Being Accurately Predicted by the Generalized Time Hardening Model

Abstract

The Fused-Deposition Modelling (FDM) technique has transformed the manufacturing discipline by simplifying operational processes and costs associated with conventional technologies, with polymeric materials being indispensable for the development of this technology. A lack of quantification of viscoelastic/plastic behavior has been noted when addressing FDM parts with Polyetherimide (PEI), which is currently being investigated as a potential material to produce functional end-products for the aerospace and health industry. Primary and secondary creep along with stress relaxation tests have been conducted on FDM PEI specimens by applying stresses from 10 to 40 MPa for 100 to 1000 min. Specimens were 3D printed by varying the part build orientation, namely XY, YZ, and XZ. Creep results were fitted to the Generalized Time Hardening equation (GTH), and then this model was used to predict stress relaxation behavior. FDM PEI parts presented an isotropic creep and stress relaxation performance. The GTH model was proven to have a significant capacity to fit viscoelastic/plastic performances for each single build orientation (r > 0.907, p < 0.001), as well as a tight prediction of the stress relaxation behavior (r > 0.998, p < 0.001). Averaged-orientation coefficients for GTH were also closely correlated with experimental creep data (r > 0.958, p < 0.001) and relaxation results data (r > 0.999, p < 0.001). FDM PEI parts showed an isotropic time-dependent behavior, which contrasts with previous publications arguing the significant effect of part build orientation on the mechanical properties of FDM parts. These findings are strengthened by the high correlation obtained between the experimental data and the averaged-coefficient GTH model, which has been proven to be a reliable tool to predict time-dependent performance in FDM parts.

Investigation of the effects of a pre-deposition heating system on the interfacial temperature and interlayer bonding strength for fused filament fabrication

“…In the future, the optimization for the laser powers with respect to printing speed and leading distance combination will be developed and how the pre-deposition heating system affects other thermal related issues, such as warping, can also be studied. Based on the research results, it also provides a potential opportunity to influence time-dependent mechanical properties such as creep behavior (Salazar-Martín et al , 2020). Furthermore, time-dependent mechanical properties study would have certainly helped evaluate functional, fatigue or life cycle performance of the laser heated 3D printed FDM part.…”

Mechanical Performance of 3D-Printed Biocompatible Polycarbonate for Biomechanical Applications

“…However, to precisely define its application areas, it is necessary to understand its mechanical performance thoroughly. It has already been shown in previous studies with engineering-grade polymers [28][29][30] that the variability of its properties is highly dependent on printing conditions. It may even be essential to use a solvent to eliminate the support material necessary to print highly complex geometric structures such as those proposed for this type of application, without this implying a deterioration of the mechanical behaviour [31,32].…”

Extrusion Additive Manufacturing of PEI Pellets

“…Most kinematic parameters were kept constant to a value that usually enhances the strength of the parts, as suggested by the technical literature [9,[11][12][13][14][15][16] on PEI 3D printing in filament form, presented in Table 2. The reflector used for the IR lights is also useful to hold the heat generated by the heated bed and the IR lights in order to generate a sort of heated chamber.…”

“…Industrially, a complete characterization of PEI AM-produced components is needed, not only regarding strength, elastic modulus, and strain at the break but also including creep behavior, isotropy, and mechanical response to given conditions. Salazar-Martin and colleagues investigated the creep behavior, isotropy, and tensile properties of PEI 9085 AM-produced parts [14]. They developed a generalized time-hardening model to predict creep behavior and concluded that the model could accurately predict the experimental response of the components during creep tests.…”

“…Additively manufactured PEI 9085 and 1010 have been investigated deeply with respect to different aspects, including mechanical properties, isotropy [14], inter-layer adhesion [15], and the possibility of using carbon nanotubes to obtain electrically conductive PEI [16]. Attention has also been given to possible post-processing techniques, including annealing [17] and hot isostatic pressing [18].…”