Composite materials have been used by humans for thousands of years, empirically our ancestors would mix natural materials to increase the strength or durability of their tools and constructions, for example, mixing clay with straw. Over time, this concept of mixing different materials to improve their performance has expanded and specialized. Today, composites play a fundamental role in high-tech applications, such as aircraft, satellites and rockets, which would not be possible without the intensive usage of these materials.
Figure 1 – Side by side ancestral composite material, bricks made of clay and straw and application of modern high-tech composites, GE90 aircraft engine, with structure and blades made of carbon fiber.
But what is a composite material after all?
According to the formal definition, a composite material (or composite) is a macroscopic combination of two or more different materials with an interface between them. The resulting composite material possesses a combination of properties that surpasses those of its individual components.
Figure 2 – Composite material examined in detail through scanning electron microscopy (carbon fiber composite).
In this definition, we find three essential elements: two different materials and an interface. In the composites widely used in industry, these materials are synthetic fiber reinforcements, such as fiberglass, carbon and kevlar, as well as polymeric matrices, such as polyester, vinyl ester and epoxy resins, among many other options available. The behavior of the composite is a result of the interaction between the fiber reinforcements, the polymeric matrix, and the fiber/matrix interface. The appropriate selection of materials, their volume ratio and orientation are extremely important as they affect properties such as density, stiffness, tensile strength, compressive strength, fatigue resistance, failure mode, thermal and electrical conductivity, flammability, chemical resistance, in addition to the associated costs.
Reinforcement, Matrix and Interface: The Cornerstones of Composite Materials
Regarding reinforcement, it is the element responsible for giving the composite material its mechanical characteristics, such as stiffness and rupture resistance, for example. Reinforcements can consist of oriented fibers, as in fabrics, or randomly oriented, as in mats. Furthermore, the reinforcements can be composed of continuous or discontinuous fibers. There is a broad range of fabrics types with oriented fibers, such as woven (WR, Twill, Satin), as well as non-woven and sewn fabrics (biaxial, triaxial and multi-axial).
Figure 3 – Different types of carbon fiber fabrics
The matrix plays a key role in the composite material. Its function is to hold fibers in place, transfer loads between fibers, and protect the fibers from environmental damage. Additionally, the matrix plays an significant role in interlaminar shear strength, compression strength and operating temperature. There are different types of matrices, including ceramic and metallic matrices, however, polymeric matrices find a much wider range of applications in the industry. These can be thermoplastic and thermosetting resins. Among the most common thermoset matrices, we can mention resins such as unsaturated polyester (UPR), vinyl ester (VE), epoxy (EP), phenolic (PF), polyurethane (PUR) and dicyclopentadiene (DCPD). As for thermoplastic matrices, some of the most used are polyamide (PA), polypropylene (PP), polyethylene (PE), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polyether imide (PEI) and polyetheretherketone (PEEK).
Figure 4 – Aeronautical component manufactured with carbon fiber prepreg and PEEK thermoplastic resin.
The performance of composites is closely tied to the interaction between the matrix and reinforcement and this interaction is influenced by the interface. We can say that the interface is the boundary surface between the matrix and the reinforcement, across which a discontinuity of properties occurs. In this area, properties such as modulus of elasticity, density and coefficient of thermal expansion, undergo a drastic change from one side to the other of this bounding surface. For example, the high stiffness of the fiber on one side meets the low stiffness of the matrix on the other. This discontinuity is made compatible through the interface. Factors such as wettability, surface tension, and roughness of the reinforcement fibers directly influence with the performance of the interface and, consequently, with the final properties of a composite.
Lee, C.H.; Khalina, A.; Lee, S.H. Importance of Interfacial Adhesion Condition on Characterization of Plant-Fiber Reinforced Polymer Composites: A Review. Polymers 2021, 13, 438. https://doi.org/10.3390/polym13030438
Figure 5 – Diagram of the interface between fiber and matrix
Figure 6 – Difference between an interface with adhesion failures (on the left) and an excellent fiber-resin interface (on the right)
The Interrelation of Materials, Design and Manufacturing Processes
When it comes to composites, it is key to keep in mind that the properties of a laminate depend on the interaction of three distinct areas of engineering: materials, design and manufacturing processes. In composites, the same material with different designs results in different final properties, as the laminate is designed taking into account not only the materials but also the orientation of the fibers and the number of layers. Similarly, the properties obtained from the same laminate design may vary depending on the chosen manufacturing process. For instance, when using different manufacturing processes on a given laminate design, the final properties will also differ.
Figure 7 – Difference in mechanical properties and fiber percentage for different manufacturing processes.
In the design of a product using composite materials, it is crucial to address some fundamental questions that will guide these three engineering areas. What are the required mechanical properties? What are the environmental conditions in which the components will be used? What is the required production scale? Based on this information, it is possible to focus efforts to meet all criteria, bearing in mind that there is no single solution to this equation, but rather a multitude of possibilities.
Why does FanTR choose to use composite materials in the manufacturing of its blades?
Composite materials offer a range of advantages, including low structural weight, high strength, the potential for optimizing mechanical properties, the ability to create complex geometries, a reduction number of components and fasteners, resistance to fatigue and resistance to corrosion.
At FanTR, our engineering team has extensive knowledge and experience in the design of large industrial fans. The company has advanced computational tools for the design and dimensioning of our products. This enables us to leverage the full geometric freedom that composite materials offer. We use fluid dynamic simulation software (CFX) for the design of high performance and low noise aerodynamic profiles. Likewise, in the structural analysis, we utilize finite element simulation software (ANSYS Mechanical) to optimize the structures, dimensioning the quantities of material, as well as fiber orientations towards the highest mechanical loads. This results in lightweight and robust components.
Figure 8 - Vacuum resin infusion process of wind blades and fan blades.
As for the manufacturing process, we use vacuum resin infusion, which produces components with a high fiber-to-resin ratio, resulting in lighter, stronger laminates with excellent repeatability control. Additionally, we have several test benches to validating our products in terms of mechanical performance, fatigue, operating temperature, aerodynamic performance and fan noise. Therefore, FanTR offers high-tech solutions, applying composite materials with excellence, positioning itself as one of the most important suppliers of industrial fans in the global market.
