Process-Structure-Property Relationship Development in Large-Format Additive Manufacturing: Fiber Alignment and...

Area of Science:

• Materials Science
• Manufacturing Engineering
• Polymer Science

Background:

• Additive manufacturing (AM) often results in mechanical anisotropy in printed parts.
• Polymer material extrusion (MEX) parts exhibit weaknesses at layer interfaces.
• Fiber alignment significantly impacts the mechanical properties of composite AM parts.

Purpose of the Study:

• To investigate the relationship between extrusion rate, fiber alignment, and ultimate tensile strength (UTS) in large-format MEX parts.
• To develop and validate methods for quantifying fiber alignment in 3D printed composites.
• To establish process-structure-property relationships for additive manufacturing.

Main Methods:

• Poly(lactic acid) with chopped carbon fiber was printed using a large-format pellet printer at varying extrusion rates.
• X-ray microscopy (XRM) was used to reconstruct the internal microstructure and analyze fiber length and orientation.
• Image analysis techniques were employed to determine fiber alignment relative to the deposition direction.
• Tensile testing was performed to measure the ultimate tensile strength (UTS).

Main Results:

• Both XRM 3D object analysis and discrete image analysis showed a negative correlation between extrusion rate and fiber alignment.
• Higher extrusion rates led to decreased fiber alignment, with slopes of -34.64% and -53.43% per extrusion multiplier, respectively.
• Increasing extrusion multiplier reduced the variation in UTS, with a minimum percent difference of 8.12 ± 14.40%.

Conclusions:

• Extrusion rate is a critical parameter influencing fiber alignment in MEX.
• Image analysis provides a viable method for correlating microstructure with meso-properties in AM parts.
• The study establishes key process-structure-property relationships for large-format additive manufacturing.