PSI - Issue 37

Md Niamul Islam et al. / Procedia Structural Integrity 37 (2022) 217–224 Md Niamul Islam et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Additive manufacturing (AM), or 3D printing, is the process used to produce 3D parts from a computer-aided design (CAD) model through layer by layer joining of raw materials (Wang et al., 2017). The advantage of this method is the ability to fabricate complex architectures with reduced material waste compared to traditional subtractive manufacturing techniques. The most widely used materials in this manufacturing process are polymers, such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyamide (PA), polycarbonate (PC) while the most common method employed to fabricate these materials into structures is fused deposition modelling (FDM) (Ngo et al., 2018). In the FDM process, the raw material is heated and melted into a semiliquid phase, which is extruded through a nozzle, solidifies and adheres to a corresponding layer, resulting in a multi-layered structure (Wang et al., 2017). The application of 3D printed materials can range from lightweight structures in aerospace industries, prosthetics and tissue/organs for medical application, complex geometries with internal structure etc. (Wang et al., 2017), depending on the type of material and fabrication process. However, the industrial applications of 3D printed parts are limited due to their poor performance compared to that of bulk polymers (Ngo et al., 2018). Hence, current research focuses on improving the strength of such materials through addition of fibres (carbon, glass, Kevlar), optimisation of printing parameters, or introduction of internal structures for improved performance (Gu et al., 2016). Still, most studies focus on quasi-static performance of these materials, while their dynamic performance was not extensively investigated. Understanding the dynamic fracture behaviour of AM polymers and composites would allow optimization of the material for more practical applications (Tsouknidas et al., 2016). The aim of this research is to investigate the dynamic fracture behaviour of AM polymer composites under ballistic impact and develop a numerical model for the fracture behaviour using finite-element analysis (FEA). The printing parameters were selected based on the material studied, and quasi-static experiments (tensile and compression tests) were carried out for mechanical characterisation of the material. 2. Methodology 2.1. Material and manufacturing method The material selected for this study was nylon reinforced with short carbon fibres (Nylon SCF) from Polymaker, printed with FDM. Nylon showed higher toughness (deformation before failure) compared to other 3D printing materials, which is essential for energy absorption in ballistic impact, while the addition of carbon fibres significantly increases the material strength (Reverte et al., 2020). A Ultimaker 2+ printer was used to fabricate solid (100% infill) structures, with the carbon fibre content in the filament of 20 wt. %. Table 1 lists the suitable printing parameters selected after multiple print tests, the literature review, and considering the manufacturer’s guide. A nozzle temperature of 260 °C was used due to high melting point of the material, while the print bed temperature was set to 50 °C for better adhesion of the printed structure to it. Also, a nozzle diameter of 0.8 mm and a layer height of 0.125 mm were used to overcome any clogging issues. The stacking order of [0°, 45°, 90°, -45°] n was used to obtain quasi-isotropic structures (Fig. 1), where n depended on the total thickness of specimens.

Table 1. Printing parameters for nylon SCF.

Printing parameters Nozzle temperature Print bed temperature

Values 260 °C

50 °C

Nozzle diameter Layer height Stacking order

0.8 mm

0.125 mm

[0°, 45°, 90°, -45°] n