PSI - Issue 35

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 35 (2022) 59–65 M.R. Khosravani and T. Reinicke / Structural Integrity Procedia 00 (2021) 000–000

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3D printing has shown favorable and unique capabilities in fabrication of structural elements with complex geome tries. In this respect, di ff erent 3D printing techniques have been used in various fields such as medicine (Nadagouda et al., 2020), construction (Marchment and Sanjayan, 2020), electronics (Khosravani and Reinicke, 2020a), jewelry (Shahrubudin et al., 2019), and automotive industry (Nicholas, 2019). Although 3D printing was used for prototypes, currently it has been utilized for fabrication of end-use products. In material extrusion technique, thermoplastic materials have been used to print components. In this method, the raw material is heated and molten material coming out of a nozzle. The component would be created layer by layer via movement of the nozzle. Fused Deposition Modeling (FDM) and Fused Filament Fabrication (FFF) are commonly used techniques based on material extrusion. FDM is widely used in di ff erent applications due to its relatively low cost, low material wastage, and ease to use (Chao´n et al., 2017). However, voids and discontinuities have been observed in 3D-printed parts based on the FDM technique. The voids introduced during the manufacturing process lead to poor mechanical strength. Therefore, influence of printing parameters on the mechanical behavior of the printed parts has been investigated in several research works (Yadav et al., 2020; Khosravani and Reinicke, 2020b; DeomoreRaykar, 2021). In this respect, printing with optimal raster orientation with an appropriate bead width can help to minimize the voids and improve mechanical performance of the 3D-printed parts. In addition, di ff erent attempts have been made to improve mechanical behavior of 3D-printed parts with the addition of fiber (Liu et al., 2018; Duigou et al., 2019; Zhang et al., 2020). This approach has been used in the polymer industry to increase strength of structural elements in traditional composites. In the field of 3D printing, fabrication of composites leads to increase the strength and improve the mechanical performance of 3D-printed parts by the incorporation of di ff erent fibers. In this context, FFF technique has been widely used to print fiber reinforced polymer composites (Matsuzaki et al., 2019; Ueda et al., 2020; Pei et al., 2021). In (Shang et al., 2020) experiments were performed to improve inter-line bonding performance of 3D-printed continuous fiber reinforced composites. In detail, a sinusoidal line shape was utilized as the fiber arrangement. The experimental results confirmed that the proposed technique increased inter-line bonding performance of the printed parts. Recently, in (Polyzos et al., 2021) numerical modeling of 3D-printed specimens reinforced with continuous fibers was presented. In this respect, the concept of representative volume element was used for the combination of matrix and fibers and good agreement between analytical models and experimental data was reported. In light of the above discussion, this study aims to investigate e ff ects of fiber on the mechanical behavior and fracture of 3D-printed polymer parts. To this aim, we have used nylon and fiberglass as matrix and reinforcement fiber, respectively. Based on a series of experimental tests on unreinforced and reinforced specimens, e ff ects of fiber on the mechanical performance and fracture behavior of the examined parts were determined. The results of tensile tests of unreinforced specimens and reinforced with fiberglass layers between pure nylon layers, were compared. The remainder of this paper is organized as follows: Section 2 presents a brief overview of reinforced 3D-printed compo nents. Details of specimen fabrication are explained in Section 3. In Section 4 experimental tests on unreinforced and reinforced parts are described. The obtained results are presented and discussed in Section 5. Finally, a short summary in Section 6 concludes the paper.

2. An overview of reinforced 3D-printed polymer parts

Material extrusion technique has been utilized for 3D printing of discontinuous fiber or continuous fiber laminates. The FDM process of continuous fiber composites was developed by Markforged. Table 1 summarizes some details of continuous fiber as reinforcement in 3D printing. Although stereolithography (SLA) and DED processes have been used for printing composites, FDM and FFF are most well-established methods for printing polymeric parts.

Table 1. 3D printer manufacturers using continuous fiber as reinforcement. Manufacturer Since Matrix

Reinforcement

Techniques

Continuous Composites

2012 2014 2015 2016

Based on requirements

Fiberglass, Kevlar, etc

SLA FDM DED FDM

Markforged

Nylon and nylon mixed with carbon fiber

Fiberglass, Kevlar, carbon fiber Fiberglass, aramid, carbon fiber

Avero

PEEK, PEI, PAEK, and PPS

Orbital Composites

Nylon

Printed composite