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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1. INTRODUCTION Additive manufacturing (AM), often referred to as 3D printing, is indeed a manufacturing process characterized by the addition of material in successive layers to create three-dimensional objects. This method stands in contrast to traditional subtractive manufacturing processes, where material is removed from a solid block to achieve the desired shape. This technological paradigm shift departs from conventional subtractive methods and offers a novel approach to the creation of intricate and precise three-dimensional objects. AM achieves this by progressively layering materials, thereby not only affording unparalleled design freedom but also enabling the fabrication of complex components with exceptional accuracy. AM's scientific significance lies in its capacity to revolutionize manufacturing processes by enabling unprecedented design flexibility, reduced material waste, and the ability to produce intricate and highly customized structures. This technology has far-reaching implications in diverse scientific and industrial fields, including aerospace(Liu et al., 2017), automotive engineering(Manela & Pogorelyuk, 2015), biomedical engineering(Murphy & Atala, 2014; Rengier et al., 2010), and materials science, where it facilitates innovations in product design, material development, and rapid prototyping. Polymers can be employed in additive manufacturing (AM) by using powder, wires, and flat sheets as input materials, and various techniques are used to melt and deposit these materials. At the heart of this additive revolution lies Polylactic Acid, or PLA, a remarkable polymer with a unique set of characteristics. PLA is celebrated for its biodegradability, absorbability, and biocompatibility, making it an invaluable material in a wide array of industries. Derived from renewable sources such as cornstarch and sugarcane, PLA aligns seamlessly with the global shift towards sustainability and environmental consciousness. Moreover, its biocompatibility renders it exceptionally well suited for applications within the ever-expanding field of biomedical devices(Silberschmidt, 2022). The most prevalent and cost-efficient technology employed for 3D printing PLA is often referred to as Fused Deposition Modeling (FDM). In FDM fabrication, the process involves the extrusion of plastic filaments through a heated nozzle. Initially, these filaments are deposited directly onto a platform known as the "build plate" to form the initial layer of material with the desired shape. The thermoplastic nature of the polymer filament is a crucial prerequisite for this method, allowing the filaments to meld together during the printing process and subsequently solidify at room temperature following printing. FDM boasts advantages such as cost-effectiveness, high printing speed, and process simplicity. Conversely, it is challenged by drawbacks such as relatively weaker mechanical properties, a visibly layered appearance, suboptimal surface quality and a limited selection of compatible thermoplastic materials.(Ngo et al., 2018) The mechanical behavior of 3D-printed components, whether under static(Ahmed & Susmel, 2018, 2019; Casavola et al., 2016; Chacón et al., 2017; Lanzotti et al., 2015) or cyclic loading(Afrose et al., 2016; Ezeh & Susmel, 2019; Jerez-Mesa et al., 2017) conditions, is influenced by a multitude of technological variables. These encompass, among others, the thickness of layers and shells, infill density, the chosen filling pattern, infill speed, the diameter and temperature of the extrusion nozzle, printing direction, feed rate, printing speed, and the temperature of the build plate(Abeykoon et al., 2020; Dezaki & Mohd Ariffin, 2020; Galvez et al., 2023; Gonabadi et al., 2022; Wu et al., 2015). These variables are critical considerations in optimizing 3D printing processes to align the material's behavior with specific application requirements(Sood et al., 2010). These considerations provide clarity on the fact that the mechanical and fatigue properties of additively manufactured (AM) polylactic acid (PLA) entail a substantial degree of complexity and in practical engineering scenarios, the static and fatigue evaluation of additively manufactured (AM) polylactic acid (PLA) can be carried out by treating it as a linear-elastic, homogeneous, and isotropic material.(Ahmed & Susmel, 2018, 2019; Ezeh & Susmel, 2019). In 3D printing, voids and layer-by-layer printing can create localized stress concentrations, somewhat similar to notches in traditional materials. When PLA is printed with less than 100% infill, it's like having intrinsic notches, which can reduce material strength. Using 100% infill is a common way to address this, ensuring a more uniform and robust structure so that’s why all specimens were printed with 100% infill level. Researchers have conducted studies that investigate the behavior of notched 3D printed PLA materials. These studies aim to understand how the presence of notches or defects, often intentionally introduced during the printing process, affects the mechanical properties and performance of PLA parts. In (Ezeh & Susmel, 2018) a large number of notched 3D printed specimens were tested to study the fatigue behavior of them, and they conclude that when stress concentration is present, the influence of the