PSI - Issue 53

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 53 (2024) 264–269

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Author name / Structural Integrity Procedia 00 (2023) 000–000

(Dagkolu et al., 2021), construction (KhosravaniHaghighi, 2022), food industry (Mantihal et al., 2020), and soft robotics (Gul et al., 2018). Considering the di ff erent uses for 3D-printed components, several engineering issues have been studied in this field. For instance, creep properties (Son et al., 2021), fracture behavior (Khosravani et al., 2023), impact behavior (Lesage et al., 2020), post-processing (KhodashenasMirzadeh, 2022), and crushing performance have been investigated in recent years. The American Society for Testing and Materials (ASTM) (ISO / ASTM 52900, 2021), has classified 3D printing into seven techniques of which material extrusion has been used in the present study. Material extrusion-based 3D printing is one of the most common AM techniques fro fabrication of parts from digital model (Truner et al., 2014). In material extrusion, a coil of of thermoplastic material is continuously fed through moving heated extruder head (Khosravani et al., 2021a). The liquefied polymers are deposited by the nozzle. This procedure is continued in order to create the physical product from the model. Fuse Deposition Modelling (FDM) is a common material extrusion process which utilizes di ff erent thermoplastics, such as nylon, polylactic acid (PLA), and polycarbonate. To create overhang features, FDM needs support structures, and these structures may be readily removed. Low initial and running costs, automated printing without supervision, and o ffi ce-friendly process are main advantages of FDM process. However, filaments are relatively large in diameter (e.g., 1.75 mm), which leads to large layer thickness. Therefore, the layers are easily visible and causes a poor surface finish. Considering continuous development of materials and techniques, 3D printing has gradually changed from a pro totype approach to a procedure that can also be used for the fabrication of functioning end-use products. parts. There fore, structural integrity and the mechanical strength of 3D-printed parts have become of significant importance. In this context, mechanical strength and sti ff ness of FDM 3D-printed parts have been investigated in previous research works (Tandon et al., 2017; KhosravaniReinicke, 2021; Stamopoulos et al., 2023). For example, in (Khosravani et al., 2021b) influence of adhesive thickness and printing parameters on the failure modes of 3D-printed single lap adhesive joints have been studied. To this aim, the specimens were fabricated under di ff erent printing conditions and a series of tensile tests were conducted under static loading conditions. Tests showed that the dominant failure mode among all samples was the cohesive failure. An extant study (Aliheidari et al., 2017) deals with a method to characterize the fracture resistance of FDM 3D-printed components. To this end, double cantilever beam specimens with a pre crack were printed and loaded in an opening mode. The researchers detected critical load at the crack initiation. The experimental findings showed an increase in the fracture resistance with the printing temperature. Since 3D-printed parts experience di ff erent environmental conditions during their service life, e ff ects of environments have been stud ied in some research works (Davoudinejad et al., 2020; Khosravani et al., 2022; PizzorniPrato, 2023). For instance, in (Khosravani et al., 2022) we used accelerated thermal ageing to investigate its e ff ects on the intact and defected 3D-printed parts. In the present study, a case study is employed to demonstrate influence of geometry on the mechanical strength of FDM 3D-printed parts. Moreover, accelerated thermal aging has been performed to show the mechanical behavior of 3D-printed parts in their service life. To this end, PLA material has been used to print specimens based on the FDM process. Particularly, the specimens with three di ff erent geometries (dumbbell-shaped, smooth, and V-notched) were fabricated. Later, some specimens were artificially aged and a series of experiments was conducted on aged and unaged test coupons. The experimental results have been evaluated and e ff ects of thermal ageing on the strength of 3D-printed parts have been determined. The rest of the paper is organized as follows: next section presents A brief overview of FDM parameters. Details of specimen preparations are described in Section 3. In Section 4, experimental investigations have been explained in detail. The results and discussion are presented in Section 5. Finally, we conclude the main findings of this research in Section 6.

2. A brief overview of parameters in FDM process

This section deals with FDM processing parameters which have influences on the performance and mechanical strength of 3D-printed parts. The FDM process is based on the extrusion of a thin fiber made of thermoplastic polymer that has been melted in a hot zone. This fiber is deposited in appropriate location on the working platform. This process is repeated until the 3D part is formed. An electric heater and temperature sensor are connected to the FDM 3D printer, which keeps the temperature within a predetermined range. In the FDM process, layer thickness within the 0.1 - 0.5 mm has been used. In the models with only horizontal and vertical walls, a change in the thickness has not significant e ff ect on the quality, but it can reduce printing process. The