CORRELATION BETWEEN INFILL DENSITY AND MECHANICAL PROPERTIES IN 3D PRINTING

Abstract

Fused Deposition Modeling (FDM) has emerged as a transformative technology in additive manufacturing, yet the precise influence of infill density on the mechanical behavior of toughened filaments, such as enhanced polylactic acid (PLA+), remains insufficiently characterized. This study systematically investigates the correlation between infill density and the mechanical properties of PLA+ specimens fabricated using a consistent grid infill pattern. To ensure a comprehensive analysis, specimens were printed with infill densities ranging from 20% to 100% at fine 10% intervals, strictly adhering to ASTM D638-14 testing standards. Statistical regression analysis revealed that both Young’s modulus and yield strength exhibit strong positive linear relationships with infill density (R² ≥ 0.98), indicating a direct proportionality between material volume and stiffness. The ultimate tensile strength was best modeled by a quadratic equation (R² = 0.98). A pivotal finding of this research is the behavior of the strength-to-weight ratio, which exhibited a non-monotonic, U-shaped characteristic (R² = 0.71) rather than a linear progression. The analysis identified optimal material efficiency at low densities (20–30%) and near-solid densities (90–100%), whereas the mid-range (40–80%) displayed diminishing returns where weight accumulation outpaced strength gains. These findings provide critical guidelines for civil and geotechnical engineering applications, such as the design of lightweight concrete formworks and scaled physical models. The derived empirical models enable engineers to predict performance and optimize printing parameters, effectively balancing structural integrity with material sustainability and cost-efficiency.