PSI - Issue 77

Pawel Madejski et al. / Procedia Structural Integrity 77 (2026) 357–364 Author name / Structural Integrity Procedia 00 (2026) 000–000

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1. Introduction

Additive manufacturing (AM), commonly referred to as 3D printing, has revolutionized modern manufacturing by enabling the production of complex, customizable geometries with minimal material waste. Among the most widely used AM techniques is fused deposition modeling (FDM), which utilizes thermoplastic filaments to build components layer by layer. Polylactic acid (PLA), a biodegradable thermoplastic derived from renewable resources, is one of the most popular materials in FDM due to its low melting point, ease of printing, and environmental friendliness (Ngo et al., 2018). Despite these advantages, the mechanical reliability of PLA parts is often compromised by inherent process induced imperfections. Defects such as microporosity, voids, and inter-layer delamination can arise due to suboptimal process parameters, material inconsistencies, or geometry-induced stress concentrations. Infill structures, which define the internal lattice pattern of printed parts, play a critical role in this regard. While infill designs directly influence material usage and weight, they also affect heat distribution during printing and, consequently, the development of internal defects. Process optimization studies (e.g., Alafaghani et al., 2017) have demonstrated that even slight variations in print temperature, speed, or layer height can significantly impact the structural integrity of FDM-printed components. As many internal defects are not visible on the surface, there is an increasing reliance on non-destructive testing (NDT) methods to assess the quality and reliability of 3D printed materials. Among the available techniques, X-ray computed tomography ( μ CT) has proven particularly effective, offering high-resolution 3D reconstructions of internal geometries. Micro-CT enables precise quantification of void content, defect morphology, and internal features, even in highly complex lattice structures (Yang et al., 2020). This capability is essential for accurately predicting mechanical behavior, especially under tensile loads, where stress concentrations around defects can lead to premature failure. Recent studies have demonstrated the value of μ CT not only in detecting porosity but also in understanding the relationship between internal defects and mechanical performance. For example, Mieloszyk et al. (2025) combined micro-computed tomography and terahertz (THz) spectroscopy to evaluate embedded fiber optics and internal structures in carbon fiber-reinforced polymers (CFRPs). Their work highlights how μ CT can reveal microstructural irregularities that are otherwise inaccessible, providing critical insights for assessing structural integrity. Building on these developments, the present study aims to bridge the gap between infill geometry, defect formation, and mechanical performance in PLA parts. Specifically, this research focuses on: 1. Developing a μ CT-based image processing workflow to isolate true material defects while excluding intentional infill voids. 2. Comparing porosity characteristics (defect count, area, and void distribution) among PLA samples printed with lines and triangles infill patterns. 3. To compute effective material density from μ CT-derived volumes and directly measured sample mass, establishing a quantitative metric for print quality and void content. Through this work, the aim is to strengthen the foundation for μ CT-assisted quality assurance in polymer-based additive manufacturing, particularly for lightweight structural components where performance depends on both internal integrity and external geometry. 2. Materials and methods 2.1. Additive manufacturing process The specimens were fabricated using a Fused Deposition Method (FDM) printer, MakerBot Sketch Large, utilizing biodegradable PLA filament (CadXpert, Poland) as the printing material. The printing process was prepared using Cura slicing software, which enabled precise control over print settings and infill structures. The 3D printing parameters used for printing bio-PLA are as follows: 100% infill density, nozzle diameter of 0.4 mm, layer height of 0.2 mm, line width of 0.4 mm, printing speed of 80 mm/s, and extrusion temperature of 220°C. The geometrical design of the samples conformed to the ISO 257-2-A standard. The sample dimensions are as follows: the total length is 170 mm, the total width is 20 mm, and the thickness is 4.2 mm. Two distinct infill geometries were selected: Lines and Triangles (shown in Figure 1). It is worth noting that the outer layer at the top and bottom used a line pattern with each thickness of 0.4.