Carbon Fiber vs Aluminum

Carbon fiber is replacing aluminum in an increasing variety of applications and has been doing so for the last few decades. These fibers are known for their exceptional strength and rigidity and are also extremely lightweight. Carbon fiber strands are combined with various resins to create composite materials. These composite materials take advantage of the properties of both fiber and resin. This article provides a comparison of the properties of carbon fiber versus aluminum, along with some pros and cons of each material.

Carbon Fiber vs Aluminum Measured

Below are the definitions of the different properties used to compare the two materials:

• Modulus of elasticity = The “stiffness” of a material. The ratio of stress to strain for a material. The slope of the stress vs strain curve for a material in its elastic region.
• Ultimate tensile strength = the maximum stress a material can withstand before breaking.
• Density = the material’s mass per unit volume.
• Specific stiffness = Modulus of elasticity divided by the material’s density. Used for comparing materials with dissimilar densities.
• Specific tensile strength = Tensile strength divided by the material’s density.

With this information in mind, the following chart compares carbon fiber and aluminum.

• Note: Many factors can affect these numbers. These are generalizations; not absolute measurements. For example, different carbon fiber materials are available with higher stiffness or strength, often with a trade-off in reduction of other properties.

  Measurement	Carbon Fiber	Aluminum	Carbon/Aluminum Comparison
  Modulus of elasticity (E) GPa	70	68.9	100%
  Tensile strength (σ) MPa	1035	450	230%
  Density (ρ) g/cm3	1.6	2.7	59%
  Specific stiffness (E/ρ)	43.8	25.6	171%
  Specific tensile strength (σ /ρ)	647	166	389%

  
  This chart shows that carbon fiber has a specific tensile strength of approximately 3.8 times that of aluminum and a specific stiffness of 1.71 times that of aluminum.

Comparing thermal properties of carbon fiber and aluminum

Two more properties that show the differences between carbon fiber and aluminum are thermal expansion and thermal conductivity.

• Thermal expansion describes how a material’s dimensions change when temperatures change.

Aluminum has approximately six times the thermal expansion of carbon fiber.

Pros and Cons

When designing advanced materials and systems, engineers must determine which material properties are most important for specific applications. When high strength-to-weight or high stiffness-to-weight matters, carbon fiber is the obvious choice. In terms of structural design, when added weight could shorten life cycles or lead to poor performance, designers should look to carbon fiber as the better building material. When toughness is essential, carbon fiber is easily combined with other materials to obtain the necessary characteristics.

Carbon fiber’s low thermal expansion properties are a significant advantage when creating products that require a high degree of precision, and dimensional stability in conditions where temperatures fluctuate: optical devices, 3D scanners, telescopes, etc.

There are also a few disadvantages to using carbon fiber. Carbon fiber does not yield. Under load, carbon fiber will bend but will not permanently conform to the new shape (elastic). Once the ultimate tensile strength of the carbon fiber material is exceeded carbon fiber fails suddenly. Engineers must understand this behavior and include safety factors to account for it when designing products. Carbon fiber parts are also significantly more expensive than aluminum because of the high cost to produce carbon fiber and the great skill and experience involved in creating high-quality composite parts.

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