Composites are simply a combination of two or more constituent materials with different physical or chemical properties. When combined, they produce a material with characteristics different from their original properties. The two main components within a composite are the matrix and fiber. The matrix is the base material while the fiber is what reinforces the material. On top of the fiber reinforcements and matrix, composites can also include core materials, fillers, additives and surface finishes to provide unique performance attributes.
Fiber-Reinforced Polymer composite (FRP)
Fiber-Reinforced Polymer – FRP is a composite made from a polymer matrix that is reinforced with an engineered, man-made or natural fiber. This combination of plastic and reinforcement fiber can produce some of the strongest, most versatile materials (for their weight) ever developed by technology. The fiber in a FRP composite includes materials like glass, carbon, aramid, basalt or natural fibers. These fibers reinforce the material and provides strength and stiffness to the composite. The matrix includes materials like polyester, epoxy, vinyl ester and polyurethane which acts as a glue to hold the fibers together and protects the fibers from damage. Due to its strong yet flexible properties, FRP can replace materials like wood, aluminum, granite and even steel.
The true term for a fiber reinforced polymer matrix composite is FRP. However, modifiers have been used to identify a specific fiber within that composite. Depending on the type of fiber, FRP name modifications can include Glass (GFRP), Carbon Fiber (CFRP) and Aramid (AFRP).
More on the FRP Polymer Matrix
The matrix is a material component of the composite which in this case is a Resin material. Resins, used in FRP composites, are either thermoset or thermoplastic.
Thermoset resins are used to make most composites. They’re converted from a liquid to a solid through a process called polymerization, or cross-linking. When used to produce finished goods, thermosetting resins are “cured” by the use of a catalyst, heat or a combination of the two. Once cured, solid thermoset resins cannot be converted back to their original liquid form. Common thermosets are polyester, vinyl ester, epoxy, and polyurethane.
Thermoplastic resins, on the other hand, are not cross-linked and, so, can be melted, formed, re-melted and re-formed. Thermoplastic resins are characterized by materials such as ABS, polyethylene, polystyrene, and polycarbonate.
Aren’t composites just plastics?
It is true that the combination of plastic and reinforcement can produce some of the best alternative materials, but this is not the case for ALL composites. The cement road you drive on every day is also a composite. Cement is simply the combination of a matrix (cement) and a reinforcement (gravel and other additives). Composites are all around us!
There are two notable composite manufacturing processes: Open molding, and closed molding. Within this, there are a variety of processing methods each with its own benefits:
Hand Lay up
Vacuum Bag Molding
Vacuum Infusion Processing
Resin Transfer molding
Reinforced and Structural Reaction Injection Molding (R-RIM & S-RIM)
Definitions & other notable terms
Additives – there are many different additives that are used to modify and enhance resin properties that become a part of the matrix. These additives include: Thixotropes, pigments & colorants, fire retardants, suppressants, UV inhibitors & Stabilizers, conductive additives, and release agents.
Closed Molding – raw materials (fibers and resins) cure inside a two-sided mold or within a vacuum bag. Typically, automated and require special equipment, so they’re mainly used in large plants that produce huge volumes of material.
Composite – a material made from two or more different materials that, when combined, are stronger than those individual materials by themselves.
Core – Core material is sandwiched between fiber reinforced laminate skins to significantly increase stiffness and flexural strength while reducing warpage of flat surfaces. Core materials include: Balsa, Cross-linked PVC Foam, Thermoplastic Foam, Polyurethane Foam, Syntactic foam, linear PVC Foam, honeycomb, PMI foam, fiber reinforced core and core fabrics (laminate bulkers).
DCPD RIM – a process for quickly, efficiently creating large parts using dicyclopentadiene resin and reaction injection molding. It utilizes a closed mold and a low-moisture, low-oxygen environment.
Dicyclopentadiene (DCPD) – DCPD resin is characterized by its low viscosity and its resistance to heat, impact, and corrosive chemicals when compared to thermoplastic resins used in standard injection molding. This allows the resulting product to be large, strong, and lightweight
Fiber – a component of a composite that reinforces the material. Provides strength and stiffness. Made of glass, carbon, aramid, basalt or natural fibers.
Fiber-Reinforced Polymer composite (FRP) – a composite made from a polymer matrix that is reinforced with an engineered, man-made or natural fiber or other reinforcing material.
Fillers – least expensive of major ingredients of a composite and help reduce the cost of composites. Can improve mechanical properties including fire and smoke performance by reducing organic content in composite laminates. Fillers include: Calcium carbonate, Kaolin, Alumina trihydrate, and calcium sulfate.
Long Fiber Injection – a process in which polyurethane resin and chopped fiberglass are sprayed into an open mold. Low compression pressure is then used to create complex parts in a variety of sizes allowing for formed geometry on both sides of the parts.
Matrix – a component of a composite. protects and transfers load between fibers.
Open Molding – raw materials (resins and fiber reinforcements) are exposed to air as they cure or harden. Open molding utilizes different processes, including hand lay-up, spray-up, casting, and filament winding.
Reinforcements – the material of fibers that help reinforce the composite. Available in reinforcement fibers and reinforcement forms.
Reinforcement Fibers – the different types of fibers that help reinforce the composite. Include Glass, Carbon, aramid (polyaramids), or new fibers.
Reinforcement forms – forms serve a wide range of processes and end-product requirements. Materials supplied as reinforcement include roving, milled fiber, chopped strands, continuous, chopped or thermoformable mat.
Reinforced Reaction Injection Molding – a process in which two or more reactive resins are metered and impingement-mixed under high pressure to form a thermosetting polymer, injected into a mold, and then cured. A popular process with a number of advantages including faster cycle times, low labor, low mold clamping pressure and low scrap rate.
Resins – the material of a matrix. Acts as a glue to hold the fibers together and protect fibers from damage. Includes polyester, epoxy, vinyl ester, polyurethane or other.
Surface finishes – used mostly for UV protection, corrosion resistance and aesthetics. Can be molded in process or secondarily applied coatings. Examples include: gel coat, surface veils, adhesives, ultraviolet protection, and both In-mold and post-mold painting.