PSI - Issue 53

Reza Ahmadi et al. / Procedia Structural Integrity 53 (2024) 97–111 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Figure 1. Schematic representation of stress and temperature trends and the three-temperature region during tensile test

The significance of this damage stress lies in its relation to fatigue strength, denoting the juncture at which an irreversible energy release occurs due to an escalation in plastic damage. In simpler terms, when the temperature trend departs from linearity, it denotes a critical macro stress responsible for provoking irreversible microplasticity within the material. This same stress can precipitate an expansion in microplasticity, ultimately culminating in the formation of microcracks during cyclic loading. Consequently, fatigue failures tend to materialize at locations where local stress is amplified by structural or surface-level micro-defects, thus precipitating plastic deformation(Henriques et al., 2018; Ma & Wang, 2018; Miller et al., 2017). The utilization of high-precision infrared sensors facilitates the creation of an experimental temperature-versus-time diagram during static tensile tests, aiding in the determination of the stress threshold at which linearity in the temperature response dissipates. (Corigliano et al., 2020) 3. Materials and Methods The specimens were fabricated using a PRUSA i3 MK3S 3D printer with a filament diameter of 1.75 mm. To facilitate the printing process, the 3D printing software PRUSA Slicer 2.5 was employed. This software, based on open-source principles, takes 3D object files in STL format, and translates them into G-code files. These G-code files contain precise instructions for generating the tool path for the printer. PRUSA Slicer 2.5 provides a range of print modes, techniques, and settings. It's important to note that constructing a part with different print modes and varying build orientations can significantly impact the strength and mechanical behavior of the final product. Consequently, selecting the optimal printing configuration is a challenging task, as the interactions between these settings are not always well-understood. This underscores the existence of substantial room for enhancement in the realm of 3D printing, as we strive to optimize the interplay between these diverse parameters for improved results. The geometry of each rapid prototyped dog-bone specimen followed the ASTM D638 (Standard Test Method for Tensile Properties of Plastics) standard, which prescribes a cross-section measuring 20mm*7 mm (Figure 2). All specimens were modelled in Ansys Space Claim 2021 R2 as shown in Figure 3. For the purposes of this study, after conducting several tests, the specimen's geometry was optimized to reduce both printing time and stress concentration(Ahmadi et al., 2023). All specimens are produced in a flat orientation on the build-plate (Figure 7). The fabrication process involved setting the nozzle temperature to 205°C, the build-plate temperature to 60°C, the initial layer print speed to 30 mm/s, and subsequent layer print speed to 90 mm/s. The shell thickness was set to 0.4 mm, and the layer height was set at 0.1 mm. Each layer began with the printing of a single perimeter line to ensure the maintenance of the desired sample geometry. It's worth noting that all specimens were manufactured with a 100% infill density. Additionally, the printing pattern for each layer was chosen to be oriented at a ±45° angle to both the X and Y axes (90° relative to each other) to ensure adequate support for each successive layer (Figure 5).