<p>As fused filament fabrication (FFF) fiber-reinforced composites are increasingly adopted in structural and load-bearing applications, understanding their fracture behavior is essential for reliable design. This study investigates the conditional fracture toughness (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\:K_Q\)</EquationSource> </InlineEquation>) and apparent energy release rate (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\:{G}_{Q}\)</EquationSource> </InlineEquation>) of glass-fiber-reinforced polyamide composites (PA6 + GF30) fabricated via FFF, with emphasis on the effects of raster orientation, notch preparation method, and specimen geometry. Four raster architectures (0°, 45°, 90°, and concentric) were evaluated using Single Edge Notch Bending (SENB) and Compact Tension (CT) specimens containing either printed notches or post-process mechanically cut notches. Full-field strain evolution and crack propagation were characterized using in situ Digital Image Correlation (DIC). The measured conditional fracture toughness values ranged from 1.35 to 5.73 MPa√m, while the apparent energy release rates ranged from 5.35 to 31.82 kJ/m². The results revealed a consistent change in orientation-dependent fracture ranking between printed and mechanically cut notch conditions, demonstrating that manufacturing-induced notch geometry strongly influences crack initiation and propagation behavior. In printed-notch specimens, the raster configuration with filaments aligned parallel to the notch direction, 0° printing orientation, exhibited the highest apparent fracture resistance due to local perimeter-wall reinforcement and localized reinforcement and improved load transfer near the notch tip. In contrast, mechanically cut notches produced higher fracture resistance in the 90° and concentric configurations by promoting crack deflection, interlayer engagement, frictional sliding, and distributed energy dissipation. The apparent energy release rate exhibited greater sensitivity to raster architecture and damage evolution than the fracture toughness, indicating that energy-based fracture metrics are more responsive to the distributed and mesostructure-dependent fracture behavior characteristic of FFF composites. The results demonstrate that fracture characterization of FFF fiber-reinforced composites requires simultaneous consideration of raster architecture, notch preparation method, and specimen geometry.</p>

Effect of Raster Orientation and Notch Preparation on Fracture Toughness and Energy Release Rate of FFF-Printed Glass Fiber-Reinforced Polyamide Composites

期刊论文
发表日期：

2026年6月20日

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Jacey Wright,
Morgan Sikes,
Kai Richard,
Peter Sheldon,
Siavash Sattar

摘要

As fused filament fabrication (FFF) fiber-reinforced composites are increasingly adopted in structural and load-bearing applications, understanding their fracture behavior is essential for reliable design. This study investigates the conditional fracture toughness ( \(\:K_Q\) ) and apparent energy release rate ( \(\:{G}_{Q}\) ) of glass-fiber-reinforced polyamide composites (PA6 + GF30) fabricated via FFF, with emphasis on the effects of raster orientation, notch preparation method, and specimen geometry. Four raster architectures (0°, 45°, 90°, and concentric) were evaluated using Single Edge Notch Bending (SENB) and Compact Tension (CT) specimens containing either printed notches or post-process mechanically cut notches. Full-field strain evolution and crack propagation were characterized using in situ Digital Image Correlation (DIC). The measured conditional fracture toughness values ranged from 1.35 to 5.73 MPa√m, while the apparent energy release rates ranged from 5.35 to 31.82 kJ/m². The results revealed a consistent change in orientation-dependent fracture ranking between printed and mechanically cut notch conditions, demonstrating that manufacturing-induced notch geometry strongly influences crack initiation and propagation behavior. In printed-notch specimens, the raster configuration with filaments aligned parallel to the notch direction, 0° printing orientation, exhibited the highest apparent fracture resistance due to local perimeter-wall reinforcement and localized reinforcement and improved load transfer near the notch tip. In contrast, mechanically cut notches produced higher fracture resistance in the 90° and concentric configurations by promoting crack deflection, interlayer engagement, frictional sliding, and distributed energy dissipation. The apparent energy release rate exhibited greater sensitivity to raster architecture and damage evolution than the fracture toughness, indicating that energy-based fracture metrics are more responsive to the distributed and mesostructure-dependent fracture behavior characteristic of FFF composites. The results demonstrate that fracture characterization of FFF fiber-reinforced composites requires simultaneous consideration of raster architecture, notch preparation method, and specimen geometry.