PSI - Issue 42

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Md Niamul Islam et al. / Procedia Structural Integrity 42 (2022) 785–792 Md Niamul Islam et al. / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction The ability to manufacture complex geometrical structures directly from computer-aided design files is considered the biggest advantage of additive manufacturing (AM) compared to traditional methods. Fused deposition modelling (FDM) is the most common technique for 3D printing of thermoplastic polymers, and studies showed that the addition of short or continuous fibres to these polymers significantly improved the overall strength and stiffness of the resultant materials (Blok et al., 2018; Peng et al., 2019). For short-fibre (SF) reinforcement, the raw filament containing a mixture of material and fibres is extruded through the same nozzle but for continuous-fibre (CF) reinforcement, separate nozzles are commonly used to print the matrix and the fibres. The addition of CFs showed better mechanical performance for 3D printed polymer matrix as a higher volume fraction of fibres can be incorporated into the structure compared to SF reinforcement (Blok et al., 2018; Peng et al., 2019). Research on the dynamic fracture of 3D printed parts is gaining attention as the fabricated structures can be modified to enhance performance based on applications. Significant research was carried out on parametric Izod/Charpy impact (Caminero et al., 2018; Zotti et al., 2018), a few experiments on drop-weight impact (Gu et al., 2016; Ko et al., 2020), and ballistic tests (Islam et al., 2021; Kao et al., 2018). Although such studies remain limited, the results show the potential of 3D printed material with impact-resistant architecture as an alternative to traditional manufacturing techniques for applications where customisation is an important aspect, such as medical applications – prosthetics, dental implants, protective gear (helmets, body armour, etc.) (Arefin et al., 2021). This study aims to expand the investigation on dynamic-fracture behaviour and modelling of AM polymer-matrix composite structures with CF reinforcement via ballistic impact. Initial mechanical characterisation tests (tensile compressive) were carried out to understand the material behaviour and performance in comparison to SF-reinforced AM composites. The dynamic-fracture results produced by impact loading were analysed, and the respective boundary conditions were reproduced using finite-element analysis (FEA) with material parameters obtained from the quasi-static tests and compared against experimental data. 2. Methodology 2.1. Material and manufacturing The raw materials used to print the composite structure were nylon and carbon fibres, obtained from Markforged. Nylon has high tensile strength and stiffness compared to other thermoplastic polymers such as PLA and ABS (Lay et al., 2019) while carbon fibres have higher tensile-compressive properties compared to glass or Kevlar fibres (Markforged, 2021). The nylon-matrix continuous carbon fibre (Nylon CCF) structures were printed using the Mark 2 printers, with manufacturing parameters listed in Table 1. Solid (100% infill) unidirectional fibre composite structures were investigated, with the fibres orientated at 0° (longitudinal orientation). The volume fraction of fibres was 20%, controlled using the Eiger software by Markforged.

Table 1. Printing parameters for nylon CCF.

Material parameter Nozzle temperature Nozzle diameter

Nylon 260 ° C 0.4 mm

Carbon fibre

260 ° C 0.9 mm

0.125 mm [45°, -45°]

0.125 mm

Layer height Orientation

[0°]