PSI - Issue 83

Manuel A.R.V. Esteves et al. / Procedia Structural Integrity 83 (2026) 146–153

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1. Introduction AM, commonly referred to as 3D printing, has experienced rapid expansion in both industrial and domestic contexts. This growth has been largely enabled by the availability of affordable and user-friendly equipment, which no longer requires advanced technical expertise for operation (Galib et al. 2025). Among the various AM technologies, FDM has become particularly widespread. For the reliable application of FDM-produced components, a thorough understanding of the mechanical behavior of printed materials is essential, as their properties are strongly influenced by processing conditions, especially extrusion temperature (Schiavone et al. 2020). Mechanical characterization of thermoplastics used in AM is typically performed according to standardized testing protocols. Tensile properties are commonly determined using ISO 527-1 or ASTM D638-14, with test equipment complying with ISO 7500-1 and ISO 9513. Key parameters include Young’s modulus, tensile and yield strength (when applicable), strain at yield and at break, and Poisson’s ratio. Flexural behavior is often evaluated following ISO 178 (Tosto et al. 2020), which provides procedures for determining the flexural modulus and stress-strain response under controlled strain rates. Impact resistance, a critical property for structural applications, is usually assessed using Charpy or Izod methods, according to ISO 179-1, ISO 179-2, or ISO 180 (dos Santos et al. 2022). The Charpy test is particularly suitable for materials susceptible to interlaminar shear fracture or environmental surface effects. In addition, thermal characterization through differential scanning calorimetry is required to identify the glass transition and melting temperatures, ensuring appropriate processing conditions during printing (Bute et al. 2023). This analysis is commonly conducted following ISO 11357-1:2016. According to ISO/ASTM 52900:2015, AM technologies can be classified into seven main categories, including Material Extrusion, under which FDM, also known as fused filament fabrication, is classified (Kafle et al. 2021). The FDM process begins with the creation of a computer-aided design model, which is exported as an standard tessellation language file and subsequently processed using slicing software to generate the machine code required for printing (Maideen et al. 2023). The suitability of polymers for FDM depends on factors such as cost, extrusion behavior, and resulting mechanical performance (Acierno and Patti 2023). In some cases, fillers such as wood particles, fibers, metal powders, or ceramics are incorporated to tailor specific properties (Fafenrot et al. 2017). The mechanical performance of FDM components is highly sensitive to printing parameters. Layer thickness has been shown to significantly influence stiffness and strength, particularly for PLA (Almansoori and Pervaiz 2023). Nozzle diameter affects dimensional accuracy, surface quality, and component density (Tanveer et al. 2022), while infill ratio governs internal porosity, balancing material usage against mechanical resistance (Ebel and Sinnemann 2014). The orientation of deposited filaments, defined by the infill angle, also plays a critical role, with reported optimal values differing between polymers such as Acrylonitrile Butadiene Styrene (ABS) and PLA (Ahn et al. 2002). Extrusion temperature is another key variable, as higher temperatures within the recommended processing range generally promote improved interlayer bonding and mechanical strength (Wittbrodt and Pearce 2015). In parallel with performance optimization, sustainability has become an increasingly important consideration in polymer-based AM. FDM processes generate substantial waste due to material purging, support structures, and failed prints, all of which contribute to increased costs and environmental impact (Guimarães et al. 2025). Recycling thermoplastic waste into new filament therefore represents a promising strategy to enhance resource efficiency. Previous studies on recycled polymers, such as Polyethylene Terephthalate Glycol, have demonstrated comparable or even slightly improved stiffness relative to virgin materials, albeit with greater variability in mechanical properties (Dohan et al. 2024). Comprehensive reviews have highlighted the technical challenges associated with polymer recycling, including material degradation, contamination, and process complexity, while also emphasizing its long-term environmental benefits (Badia et al. 2012). Recycling has been shown to reduce both energy consumption and carbon footprint when compared to virgin material production (Brüster et al. 2016). With specific regard to PLA, existing research indicates that repeated recycling cycles lead to molecular degradation and progressive reductions in mechanical performance (Badia et al. 2012). While one or two recycling cycles may result in flexural properties close to those of virgin PLA, additional cycles can cause a pronounced deterioration in strength and consistency (Lanzotti et al. 2019). These findings underline the need for further investigation into the processing conditions that can mitigate degradation effects. In this context, the present study evaluates the fracture behavior of recycled PLA processed by FDM, focusing on the influence of extrusion temperature. Charpy impact specimens were produced using virgin PLA as a reference and