Why can carbon fiber composite materials replace traditional metal materials in industrial applications?

The emergence of carbon fiber can be traced back to 1963. At that time, carbon fiber was very expensive and was only used in the manufacture of military aviation and spacecraft. However, the lightweight properties of carbon fiber make it gradually replace metal structural parts, thereby achieving faster development.

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In the late 1970s, the Formula One team had a keen interest in carbon fiber composites. Subsequently, McLaren used carbon fiber composites for the first time. The MP4/1-Pioneer Formula One racing car made in 1981 was made of carbon fiber composites (total weight 585 kg/1289 pounds). Today, almost every Formula One car is made of carbon fiber.

 

The reason why carbon fiber composite materials can replace traditional metal materials mainly depends on the following excellent characteristics:

 

Low density and light weight

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Carbon fiber composite materials have the characteristics of low density and low quality. The density of carbon fiber composite material is 1.55g/cm³ (calculated based on 30% epoxy resin and 70% carbon fiber), compared with 2.7g/cm³ for aluminum, 4.5g/cm³ for titanium, and 7.9g/cm³ for steel .

 

Regarding the weight of the material, what does it mean in practice? For example, consider a 1×1 meter thick and 1 cm (10 mm) thick sheet according to the same size structural material. Depending on the material, the quality of the sheet is as follows:

The weight of the carbon fiber composite material component is 15.5kg;

The weight of aluminum components is 27kg;

The weight of the titanium component is 45kg;

The weight of steel components is 79kg.

 

In other words, the weight of carbon fiber composite materials will be 42% lighter than aluminum, 3 times lighter than titanium, and 5 times lighter than steel.

 

High stiffness

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Carbon fiber composite material has high rigidity. The rigidity of carbon fiber composite material prepared by using standard fabric and 0/90 weaving process and prepreg technology is 90.5 GPa (Young’s modulus), while aluminum is 69 GPa. In addition, carbon fiber composite materials are 42% lighter than aluminum materials of the same thickness. The above calculation refers to components of the same thickness.

 

If weight is the first priority and the design engineer shall not exceed the 1kg weight limit, carbon fiber composite materials made of standard fabric (twill) will provide two times higher stiffness than aluminum and steel, and when in use, if it is single For fabrics, it is almost 4-5 times higher.

 

The high rigidity and low density of carbon fiber composite materials can be thicker when processing the same weight products. For example, for a 1.5mm thick steel component, the thickness of the same part made of aluminum is 4mm, while the thickness of a part made of carbon fiber is 7mm. Simply put, the thickness of the material is increased by 2 times, and the stiffness is about 8 times the original. This provides many opportunities to reduce weight through the use of carbon fiber.

 

Low thermal expansion

The coefficient of thermal expansion (CTE) of carbon fiber composites is very low. The linear thermal expansion coefficient of carbon fiber at 20°C is 2 (10⁻⁶/°C). The comparison of other structural materials at the same temperature of 20℃ is as follows:

▲ Titanium 8 (10⁻⁶/°C);

▲ Steel 11 (10⁻⁶/°C);

▲ Stainless steel is 17 (10⁻⁶/°C);

▲ Aluminum 23 (10⁻⁶/°C).

 

In other words, the thermal expansion of carbon fiber composites is 4 times lower than titanium, 5.5 times lower than steel, 8.5 times lower than stainless steel, and 11.5 times lower than aluminum.

 

Anisotropy

 

Unlike metals, carbon fiber composite materials are anisotropic materials. Therefore, the stiffness and other properties of composite materials depend on the orientation of the fibers. As far as metals are concerned, these properties are always the same regardless of the orientation, and these materials are called isotropic materials. This is a significant difference between carbon fiber composite and metal.

 

Carbon fiber composite material is similar to wood, and its strength and rigidity depend on the texture and ring pattern. In the production of carbon fiber structural parts, it is necessary to determine the orientation of the carbon fiber and the type of fabric. For example, there are unidirectional fabrics (UD), bidirectional fabrics (such as plain or twill), and fabrics made of UD fabrics in different directions, such as biaxial and triaxial.

 

This production process can achieve the best composite, that is, to ensure that more fabrics can withstand high loads, while reducing fabrics where the load is limited. In addition, in addition to controlling the number of fabrics and the thickness of the unit, the process also ensures that the orientation of the fabric is controlled according to the actual load in actual production. Therefore, compared with structural parts made of metal, the weight of the elements can be significantly reduced.

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Post time: Jul-06-2021