Carbon Fiber CFRP properties
Carbon fiber reinforced polymer (CFRP) is a composite material that combines high-strength and high-stiffness carbon fibers with a polymer matrix, usually thermosetting. The fiber volume fraction typically ranges between 50% and 70%, giving it an exceptional strength-to-weight ratio, up to five times that of structural steel. It is mainly used in sectors where mass reduction is critical without sacrificing mechanical performance.
Chemical composition
Section titled “Chemical composition”The typical composition of a cured CFRP laminate with epoxy matrix is summarized in the following table.
| Component | Typical Content (% vol.) |
|---|---|
| Carbon fiber (PAN-based, >92% C) | 55 – 65 |
| Epoxy matrix (diglycidyl ether of bisphenol A, amines) | 35 – 45 |
| Additives (mold release agents, UV absorbers, hardeners) | < 2 |
Carbon fibers are classified according to their precursor (PAN, pitch) and their elastic modulus. AS-4 type fibers (PAN) have a carbon content greater than 93%, with traces of nitrogen and hydrogen, while the matrix is an irreversible crosslinked network in thermosetting systems. In applications requiring higher toughness or recyclability, thermoplastic matrices (PEEK) or epoxy vitrimers with dynamic bonds are used.
Mechanical properties
Section titled “Mechanical properties”The mechanical properties are presented for the two representative states: dry carbon fiber and unidirectional laminate cured with epoxy (60% vol. fiber, 0° orientation).
Carbon fiber (reinforcement)
Section titled “Carbon fiber (reinforcement)”| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Tensile strength | 4000 – 4900 MPa | 578 – 710 ksi |
| Tensile modulus (Young) | 245 – 317 GPa | 35.5 – 46.0 Msi |
| Elongation at break | 1.6 – 1.7 % | 1.6 – 1.7 % |
| Density | 1744 – 1800 kg/m³ | 0.063 – 0.065 lb/in³ |
Data source for AS‑4 and IM‑7 fibers: Engineering Toolbox.
Unidirectional CFRP laminate (epoxy matrix, 60% vol. fiber)
Section titled “Unidirectional CFRP laminate (epoxy matrix, 60% vol. fiber)”| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Longitudinal tensile strength | 1500 MPa | 217 ksi |
| Longitudinal tensile modulus | 140 GPa | 20.3 Msi |
| Flexural strength | 1200 MPa | 174 ksi |
| Flexural modulus | 130 GPa | 18.9 Msi |
| Elongation at break | 1.0 – 1.5 % | 1.0 – 1.5 % |
| Interlaminar shear strength (ILSS) | 60 – 80 MPa | 8.7 – 11.6 ksi |
A vitrimer-epoxy laminate with three layers of carbon fabric has shown a tensile strength of 356 MPa, comparable to that of conventional CFRP (source: AZoM). Fracture is brittle, with virtually no plastic deformation (< 0.5% strain until failure).
Physical properties
Section titled “Physical properties”| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Laminate density | 1.55 g/cm³ | 0.056 lb/in³ |
| Carbon fiber density | 1.8 g/cm³ | 0.065 lb/in³ |
| Color | Black | – |
| Moisture absorption (24 h, 23 °C) | 0.1 – 0.3 % | – |
| Poisson’s ratio (longitudinal-transverse) | 0.25 – 0.30 | – |
The low density of the composite, almost 80% lower than that of steel, is one of the main reasons for its use in structural weight reduction.
Thermal properties
Section titled “Thermal properties”| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Standard epoxy glass transition temperature (Tg) | 120 – 180 °C | 250 – 355 °F |
| Maximum continuous service temperature | 150 °C | 302 °F |
| Thermal conductivity (longitudinal) | 5 – 10 W/(m·K) | 2.9 – 5.8 Btu·in/(h·ft²·°F) |
| Coefficient of thermal expansion (CTE longitudinal) | 0.1 – 1.0 × 10⁻⁶ /°C | 0.06 – 0.56 × 10⁻⁶ /°F |
| Vitrimer thermal stability (processable >) | 200 °C | 392 °F |
The very low longitudinal thermal expansion gives CFRP dimensional stability practically unmatched by metals. Vitrimer systems provide reprocessing capability at temperatures above 200°C without loss of mechanical properties.
Typical processing
Section titled “Typical processing”CFRP laminates are manufactured by manual or automatic stacking of prepregs followed by autoclave curing (pressure 6 bar, temperature 120–180°C). Other processes include resin transfer molding (RTM), filament winding, and pultrusion. The emergence of vitrimer resins also allows the application of thermoplastic techniques such as compression molding at >200°C, facilitating recycling and repair.
Applications by industry
Section titled “Applications by industry”| Industry | Application examples |
|---|---|
| Aerospace | Aircraft fuselages, wings, stabilizers, engine nacelles. |
| Automotive | Competition monocoques, body panels, drive shafts. |
| Sports | Bicycle frames, tennis rackets, fishing rods, helmets. |
| Marine | High-performance boat hulls, masts. |
| Civil construction | Reinforcement of concrete structures, bridges, prestressing bars. |
| Energy | Wind turbine blades, compressed gas vessels (hydrogen tanks). |
Comparison with other materials
Section titled “Comparison with other materials”| Material | Density (g/cm³) | Tensile strength (MPa) | Specific strength (kN·m/kg) | Elastic modulus (GPa) |
|---|---|---|---|---|
| Unidirectional CFRP (60% fiber) | 1.55 | 1500 | 968 | 140 |
| Structural steel S275 | 7.85 | 430 – 580 | 55 – 74 | 210 |
| Aluminum 7075‑T6 | 2.80 | 540 | 193 | 71 |
| GFRP (E-glass/epoxy, 60% fiber) | 2.0 | 1000 | 500 | 40 |
CFRP exceeds steel in specific strength by a factor of more than 15 and offers a specific modulus comparable to that of steel, with a dramatic weight advantage.
Advantages and limitations
Section titled “Advantages and limitations”Advantages
- Extremely high strength-to-weight and stiffness-to-weight ratios.
- Fatigue and corrosion resistance much superior to metals.
- Nearly zero coefficient of thermal expansion.
- Possibility to orient fibers to optimize directional loads.
Limitations
- High raw material and processing cost.
- Brittle and catastrophic failure, difficult to predict.
- Difficult recyclability in traditional thermosetting systems (being solved with vitrimers).
- Impact sensitivity and low interlaminar strength.
Standards and norms
Section titled “Standards and norms”CFRP tests and specifications are governed by ASTM and ISO standards. Some of the most commonly used are:
- ASTM D3039: Tensile test for polymer matrix composite materials.
- ASTM D790: Flexure test.
- ASTM D2344: Interlaminar shear strength (short-beam).
- ASTM D3410: Compression test.
- ISO 527‑4/-5: Tensile properties of reinforced plastics.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the typical tensile strength of CFRP?
Section titled “What is the typical tensile strength of CFRP?”The longitudinal tensile strength of a unidirectional CFRP laminate with 60% fiber reaches 1500 MPa (217 ksi), while the isolated carbon fiber can exceed 4000 MPa (578 ksi).
What elastic modulus does it have?
Section titled “What elastic modulus does it have?”The Young’s modulus of the laminate is around 140 GPa (20.3 Msi), about ten times that of glass-reinforced nylon and comparable to steel (210 GPa) but with three-quarters less weight.
What is the density of the material?
Section titled “What is the density of the material?”The density of CFRP ranges between 1.5 and 1.6 g/cm³ (0.054‑0.058 lb/in³), approximately 1.55 g/cm³ (0.056 lb/in³) for a standard epoxy-carbon composite.
What maximum temperature can it work at?
Section titled “What maximum temperature can it work at?”The continuous service temperature for standard epoxy matrices is around 150 °C (302 °F). Systems with PEEK resin or vitrimers can temporarily exceed 200 °C (392 °F) without degradation.
Is it possible to recycle CFRP?
Section titled “Is it possible to recycle CFRP?”Yes, the development of vitrimer matrices has enabled a hydrothermal degradation process in water at 160 °C (320 °F) without catalyst, allowing recovery of carbon fibers with tensile strength similar to that of virgin fibers.
How much does a CFRP part weigh compared to steel?
Section titled “How much does a CFRP part weigh compared to steel?”A CFRP part weighs approximately 70% less than an equivalent structural steel part, reducing mass from 100 kg to 30 kg in many aeronautical components.
References
Section titled “References”- azom.com: https://www.azom.com/article.aspx?ArticleID=20111
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/polymer-composite-fibers-d_1226.html
- steelnumber.com: https://www.steelnumber.com/en/steel_alloy_composition_eu.php?name_id=1361