Author: [Bruce Zhou]
Affiliation: [Jota Machinery Composites Material Prepreg Solution]
Corresponding Author: [jotamachinery@gmail.com]
Published : December 05 , 2025

Abstract

Carbon fiber additive manufacturing (AM) has progressed into a viable route for producing lightweight and mechanically efficient structures for aerospace, automotive, robotics, and industrial applications. This review examines two dominant reinforcement strategies in fused-filament and extrusion-based AM: continuous carbon fiber (C-CF) and short carbon fiber (S-CF) composites. Using published mechanical benchmarks, the paper compares tensile and flexural performance, interlayer behavior, void formation, and microstructural mechanisms that govern stiffness, strength, and fracture. Continuous fiber systems, implemented through in-nozzle impregnation, dual-nozzle deposition, laser-assisted extrusion, laminated-object manufacturing (LOM), and pultruded hybrid feedstocks, routinely achieve tensile strengths approaching 986 MPa and moduli above 125 GPa. Short fiber systems, though more economical and compatible with standard FDM hardware, deliver modest improvements in stiffness (≈2–30%), fracture toughness (≈40–80%), and modulus (≈30%) at moderate fiber loadings. The review also identifies anisotropy, interlayer adhesion, voids, and geometric constraints as persistent challenges for structural certification. Future research must integrate process modeling, fiber path optimization, and interfacial engineering to unlock the full potential of carbon fiber AM.

Keywords

Carbon fiber additive manufacturing; continuous fiber composites; short fiber composites; fused deposition modeling; interlayer adhesion; fiber orientation; process–structure–property relationships.

1. Introduction

Additive manufacturing of fiber-reinforced polymers is rapidly transforming composite fabrication due to its ability to produce geometrically complex, lightweight, and topology-optimized components. Carbon fiber, with its high strength-to-weight ratio, thermal stability, and conductivity, is an ideal reinforcement for structural AM applications. However, successful integration of fibers within thermoplastic matrices requires controlling alignment, impregnation, interlayer fusion, and void content—parameters that profoundly influence final performance [2–6].

Two major categories of carbon fiber AM have emerged:

1. Continuous carbon fiber (C-CF) printing — leveraging uninterrupted fiber bundles for structural-level performance.
2. Short carbon fiber (S-CF) printing — relying on pre-compounded filaments for improved stiffness and ease of processing.

This paper synthesizes the mechanical, microstructural, and process-specific insights from recent literature, establishing a technical baseline for advanced composite AM.

2. Continuous Carbon Fiber AM

2.1 Technologies

2.1.1 In-Nozzle Impregnation

First demonstrated by Matsuzaki et al. [2], dry carbon tow and thermoplastic filament converge in a heated nozzle for in-situ impregnation. This approach improves alignment and reduces porosity relative to ex-nozzle methods.

2.1.2 Dual-Nozzle Systems (Markforged Architecture)

Dual-nozzle deposition systems extrude matrix material and continuous fibers separately. Works by Dickson et al. [5], Van der Klift et al. [6], and Melenka et al. [7] characterize fiber placement accuracy and its influence on stiffness and tensile response.

2.1.3 Laser-Assisted C-CF/PEEK

Laser preheating during deposition enhances polymer mobility and fiber wet-out. Luo et al. [8] report interlaminar shear strength exceeding 35 MPa and flexural strength above 480 MPa—notable for semi-crystalline PEEK systems.

2.1.4 Laminated Object Manufacturing (LOM & LA-LOM)

Parandoush et al. [10] and Chang et al. [11] adapted CF/PEEK prepreg sheets into layerwise AM, achieving tensile strengths up to 1514 MPa and flexural moduli above 125 GPa after hot-pressing consolidation.

2.1.5 Microwave & Thermal Stabilization Control

Microwave-assisted deposition improves thermal uniformity, reducing voids and bead discontinuities [13].

2.1.6 Pultruded CF/PA6 Hybrid Feedstocks

Zhuo et al. [15] achieve fiber volume fractions up to 44–47%, substantially higher than typical FDM capabilities.

2.2 Mechanical Performance

Continuous fiber composites surpass all other polymer AM systems in structural metrics.

Benchmark Properties

Study	Material System	Tensile Strength	Modulus	Notes
Blok et al. [19]	CF-Nylon	986 MPa	64 GPa	Markforged system
Luo et al. [8]	CF-PEEK	—	35 MPa ILSS; Flexural >480 MPa	Laser-assisted
Chang et al. [11]	CF-PEEK	1514 MPa	133 GPa	LA-LOM + HPP
Tian et al. [3]	CF-PLA	—	30 GPa modulus; 335 MPa flexural	Vf = 27%
Li et al. [3]	CF-PLA	+164% flexural strength	+351% storage modulus	Preprocessing

These values approach or exceed traditional unidirectional thermoplastic composites.

2.3 Process–Structure Limitations

Several microstructural factors limit performance and scalability:

1. Interlayer Debonding
   Observed in interlaminar fracture studies [30–31].
2. Void Formation
   A primary defect documented across continuous AM systems [14].
3. Fiber Steering Restrictions
   Sharp-radius turns cause tow buckling or segmentation [5–6].
4. Limited Fiber Volume Fraction
   Except in pultruded systems, typical Vf is 10–27%.
5. Thermal Gradient Effects
   Nonuniform crystallinity in high-temperature matrices such as PEEK [32].

3. Short Carbon Fiber AM

3.1 Processing Characteristics

Short fiber filaments are compatible with standard FDM hardware and rely on melt-flow alignment. Mechanical response depends heavily on fiber length, orientation, dispersion, and fiber–matrix interfacial bonding [16–18].

3.2 Mechanical Properties

PLA + CF — Ferreira et al. [16]

• +2.2% longitudinal modulus
• +25% transverse modulus
• +16% shear modulus
  Strength did not increase significantly due to weak fiber adhesion.

ABS/PA + CF — Ning et al. [17]

At 5–7.5 wt% CF:

• +22.5% tensile strength
• +30.5% tensile modulus

Higher CF contents increased brittleness and porosity.

Fracture Properties — Papon et al. [18]

At 5 wt% CF:

• +42% fracture toughness
• +77% fracture energy
  Square nozzles improved bead junction area and reduced voids.

Continuous vs Short Fiber — Blok et al. [19]

• Continuous CF: 986 MPa tensile
• Short CF: 33 MPa tensile

A >10× performance difference underscores the critical role of fiber continuity.

4. Comparative Analysis

Short fiber composites improve stiffness and fracture resistance but are not suited for structural load-bearing. Continuous fiber composites deliver an order-of-magnitude gains in strength but require specialized hardware and careful thermal management.

Key failure modes:

• Delamination at interlayer boundaries
• Fiber–matrix debonding
• Crack initiation at voids and bead interfaces

5. Future Directions

Key areas for advancement include:

5.1 Interlayer Fusion Techniques

Laser preheat, compaction rollers, and ultrasonic consolidation may improve cohesion.

5.2 Fiber Path Optimization

Stress-aligned fiber steering algorithms are needed for aerospace-level design.

5.3 High-Temperature Thermoplastics

PEEK/PEKK/PEI deposition requires precise thermal control to avoid crystallinity gradients [32].

5.4 Standardized Qualification Protocols

Fatigue, creep, impact, radiation exposure, and vacuum stability must be evaluated for space applications.

5.5 Hybrid Reinforcement

Combining long and short fibers may balance manufacturability and performance.

6. Conclusions

Carbon fiber 3D printing provides unmatched versatility for customized composite structures. Continuous fiber systems produce mechanical properties comparable to traditional laminates, while short fiber composites offer accessible stiffness improvements for conventional FDM systems. However, certification-level adoption requires mastering void control, interlayer cohesion, fiber steering, and thermal uniformity.

Future progress depends on integrating materials science, process modeling, automated fiber placement, and in situ quality monitoring. With these advancements, carbon fiber AM may enter mainstream aerospace and high-performance manufacturing.

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