Abigail Batley, Engineering Design Lecturer at Bournemouth University tackles the data sheets of three carbon fibre composites.
As additive manufacturing (AM) matures, the use of carbon fibre composites has increased, promising lightweight, high-strength solutions for critical applications in demanding industries. Despite the appeal of manufacturer-provided data sheets, discrepancies between these claims and real-world performance persist. My recent study evaluated the tensile strength, repeatability, and print quality of three carbon fibre-reinforced AM materials, providing insight on their actual performance and reliability.
The research focused on three materials utilising OEM-recommended parameters:
ABS-CF10 – A Stratasys material with 10% chopped carbon fibre, designed for greater strength and stiffness than standard ABS.
Onyx – Markforged’s nylon base reinforced with micro carbon fibre, known for enhanced toughness and stiffness.
Onyx + Continuous Carbon Fiber – Reinforced with continuous strands of carbon fibre, touted for delivering significant strength improvements.
Dog-bone specimens were printed following ASTM D638 standards and subjected to tensile testing using digital image correlation (DIC) to map strain distribution and assess mechanical properties. Microscopy analysis provided detailed insights into print quality, defects, and the microstructure of the composites.
DISPARITIES IN TENSILE STRENGTH
The study uncovered a mix of overperformance and underperformance compared to manufacturers’ claims:
• ABS-CF10 fell short of expectations, achieving tensile strength 12.36% lower than advertised. Weak fibre-matrix adhesion and large voids were identified as primary contributors.
• Onyx exceeded the manufacturer’s stated tensile strength by 8.66%. Consistent bonding and minimal voids highlighted the advantages of proper process controls and material quality.
• Onyx + Continuous Carbon Fiber delivered 15.31% higher tensile strength than claimed but also exhibited the lowest repeatability and dimensional accuracy among the three materials.
This variability presents challenges in achieving uniformity across parts, even when using the same printer and build parameters.
PRINT QUALITY
Microscopy analysis revealed that the quality of fibre-matrix wetting and void content significantly influenced mechanical properties. Poor fibre-matrix wetting in ABS-CF10 led to weak interfacial bonding, limiting load transfer and resulting in fibre pullout during tensile testing. This issue, coupled with the presence of large voids, reduced the material’s strength below expectations.
In contrast, Onyx demonstrated good wetting, even fibre distribution, and low void percentages. These characteristics allowed for better load transfer and overall structural integrity, leading to its superior performance. Onyx + Continuous Carbon Fiber, while strong, revealed larger voids around the reinforcement layers, affecting repeatability and dimensional precision.
REPEATABILITY CHALLENGES
The incorporation of continuous carbon fibre presents a double-edged sword. While it significantly boosts tensile strength, its inclusion complicates the manufacturing process, reducing consistency between builds. The study’s tensile tests showed wider deviations in strength for Onyx + Continuous Carbon Fiber compared to the other materials. Stress-strain graphs further revealed a two-phase response: the composite’s stiffness diminished after the carbon fibre layers failed, with only the nylon matrix remaining to carry the load.
This variability underscores the challenges of reliably integrating continuous fibre reinforcement into printed parts.
IMPLICATIONS FOR INDUSTRY
Data Sheets as Guidelines, Not Guarantees: While OEMs provide baseline data, actual performance depends heavily on printer calibration, material quality, and adherence to optimal print settings. Engineers should validate materials for specific applications rather than relying solely on published specifications.
Quality Control: Meticulous attention to print parameters, such as layer height, infill patterns, and build orientation, can greatly influence performance. Quality control measures, such as ensuring new filament reels and using calibrated printers, were key to achieving high-performance results.
Balancing Strength and Repeatability:
For applications demanding consistent results across multiple builds, chopped carbon fibre composites like ABS-CF10 or Onyx may offer more predictable performance. However, for applications where strength is the primary concern, continuous fibre composites like Onyx + Continuous Carbon Fiber remain unmatched, albeit at the cost of repeatability and dimensional accuracy.
The use of carbon fibre composites in AM continues to expand the possibilities for high-performance parts. However, as this study shows, discrepancies between manufacturer claims and real-world performance remain a critical issue. Designers and engineers must approach material selection and validation with care, understanding that factors such as fibre-matrix wetting, void content, and print quality significantly impact results.
For the AM industry to fully realise the potential of carbon fibre composites, bridging the gap between advertised and actual performance is essential. With better process controls, rigorous testing, and a commitment to transparency, AM can deliver on its promise of producing reliable, high-strength components for the most demanding applications.
