PSI - Issue 37

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 37 (2022) 97–104 Mohammad Reza Khosravani et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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manufacturing processes. For instance, 3D printing has exceedingly reduced fabrication cost and time with flexibility in printing complex geometries Utela et al. (2008). Indeed, the use of 3D printing provides the production of any kind of shape from a digital design with a little waste of raw materials Wimpenny et al. (2017). 3D printing has indicated advantages in fabrication of complex structures, multi-material structural elements, and thin-walled structures Amirpour et al. (2019), Yuan et al. (2020), Zhang et al. (2021). Currently, 3D printing technology has been widely used in different fields such as electronics Khosravani and Reinicke (2020), construction industry Souza et al. (2020), manufacturing Sandeep et al. (2021), and healthcare monitoring Nasiri and Khosravani (2020). American Society for Testing Materials (ASTM) classified 3D printing technology in seven methods: material extrusion, binder jetting, directed energy deposition, material jetting, powder bed fusion, sheet lamination, and vat photo polymerization ASTM F2792 (2012). Fused Deposition Modeling (FDM) is a 3D printing technique based on material extrusion that is commonly used due to its simplicity, material availability, and reliability. Over the years, different 3D printing techniques have been utilized to fabricate components using a wide range of materials such as stainless steel, ceramics, polymers, and titanium. Different thermoplastic polymer filaments have been used in fabrication of 3D-printed components, and Polylactic Acid (PLA) is one of the most popular materials utilized in the FDM process. The FDM process showed flexibility in design of structural elements and it can significantly increase the application of materials in different fields. This 3D printing process deals with several printing parameters (e.g., nozzle temperature, printing speed, and bed temperature) and these parameters play important roles on the mechanical performance of the 3D printed parts Wang et al. (2019), Peng et al. (2020), Chen et al. (2021). Although FDM process has been used for fabrication of different parts, FDM 3D-printed parts are not strong enough for some applications. In this respect, several methods and techniques have been developed and investigated to increase strength of the FDM 3D-printed parts Koch et al. (2017), Lay et al. (2019), McLouth et al. (2021). For instance, in Jing et al. (2021) a facile strategy has been used to enhance interlaminar bonding strength of FDM 3D-printed components. To this aim, microwave irradiation, ball milling, and FDM process are combined to prepare composite parts. The obtained results confirmed that the utilized strategy is promising for fabrication of high performance 3D printed parts. Despite a good printability of PLA material, its crystalline phase limits utilizing 3D-printed parts. Moreover, in several research works effects of adding fibers in strength improvement of FDM 3D-printed parts were investigated Sang et al. (2019), Sugiyama et al. (2020), Prajapati et al. (2021). Wood is an organic material and its powder can be used for printing in combination with different materials. Currently, it has been utilized in thermoplastic composite industry because of low price, renewability, high modulus, and good machinability Ayrilmis (2018), Deb and Jafferson (2021). Adding wood to PLA leads to a decrease in price of filament, but further investigation in mechanical characterization of 3D-printed PLA-wood composite is required. Similar to other manufacturing processes, different manufacturing defects can occur during 3D printing process. Since the defects and anomalies (e.g., overlaps, gaps, and offset) can change mechanical performance of the parts, study influence of these manufacturing defects on the structural integrity of the 3D-printed parts is a necessity. Although numerous research works have been conducted on the fracture of 3D-printed parts, a few studies have investigated effects of manufacturing defects on the mechanical performance of 3D-printed structural elements. In the present study, intact and defected PLA-wood specimens were examined. To this aim, test coupons with different raster orientations based on the FDM process. In the defected specimens, a gap was designed and intentionally placed into the specimens. It should be noted that the gaps were oriented with the raster directions in different specimens. It is noteworthy that among the design and printing parameters, only raster direction and the inclusion of defects were changed in different specimens. Here, a series of tensile tests was performed under static loading conditions. Based on the obtained results, effects of the certain defect (gaps) on the mechanical performance and structural integrity of the examined 3D-printed parts have been determined. The present study is an attempt to provide reliable data for next structures’ design. Moreover, the presented results would be beneficial for the future finite element models. The reminder of this paper is structured as follows: in the subsequent section, an overview of fracture in 3D-printed polymer components is presented. The details of specimen preparation and experimental tests are described in Section 3. The obtained results are presented and discussed in Section 4. Finally, a short conclusion has been furnished in Section 5.