At present, as a common reinforcement fiber for composite materials, there are usually three types: carbon fiber, glass fiber and Kevlar (aramid) fiber.

When used for composite reinforcement, the fibers can define the performance standards of the material and are responsible for playing a load-bearing role in the design structure, while the resin matrix is primarily responsible for transferring the load to the fibers.

In short, the choice of fiber type is an integral part of the design process.

For the three reinforced fibers mentioned above, there are often thousands of properties that need to be weighed when deciding what material to use for a given project.

Factors and characteristics such as modulus, tensile strength, compressive strength, toughness, stiffness, electrical conductivity and chemical/corrosion resistance are all important when selecting fibers for use.

While there are thousands of material properties to choose from, choosing the right fiber at the beginning of a project design will effectively mitigate challenges throughout the project and point to the best raw material.

Typically, composite structures use more than one fiber to achieve the design requirements required for end use. Although there are countless fiber characteristics that can further define the end use of a structural part, the following advanced features provide advanced features for defining the purpose of the design:

Fiber modulus is the change in length that a fiber experiences when subjected to an increased load. This load can be compressive or tensile. The calculation method is stress divided by strain. The modulus usually indicates the stiffness of a material. On a given stress/strain curve, it is called the slope of the line.

Most fibers are classified by modulus because it helps determine the stiffness of the composite.

In general, composites using carbon fiber, glass fiber, and Kevlar are all classified as brittle and have little to no stretch when broken compared to more plastic or non-brittle materials.

Tensile strength is the ability of a material to withstand a load when stretched. It is the maximum force or load applied before the fiber is permanently deformed, as shown in the figure, carbon fiber has advantages in strength and strength-to-weight ratio, such as Japan's Toray T800S strength-to-weight ratio of up to 3266, the highest value of all the reinforced fibers listed in the table. However, there are significant differences between S-glass fibers and E-glass fibers.

In terms of density, Kevlar is the lightest material, as shown in the table above, the body density of Kevlar fiber is only 1.44g/cm3. Although Kevlar has the lowest ultimate strength, in terms of strength-to-weight ratio, it surpasses glass fiber, but is slightly lower than carbon fiber. From an economic point of view, if ultimate strength is the only design criterion, then e-glass fiber is the first choice.