Composites

Table of Contents

What Are Composites?

Composites are uniform materials comprised of at least 2 different elements, which combine to yield a product possessing different properties and characteristics than those elements by themselves. The material composition of composites generally includes layers of fibre reinforcement oriented to give strength, held together by a bulk component called the matrix [1]. Composite materials are favoured because they can be stronger, lighter, and more cost-effective compared to other common materials such as aluminum and stainless steel [2][3].

Main Types of Composites

Today, there are usually 3 main types of man made composites which all vary in formation and exhibit different chemical and mechanical properties. As a result, they are often found in a wide variety of different industries [1].

• PMC: Polymer Matrix Composites use a resin (epoxy) as the matrix, and certain fibers (carbon fiber, fiberglass) as the structural reinforcement. Polymer Matrix Composites are the most common types of composites as a result of its ability to be transformed to complex shapes [1].

• MMC: Metal Matrix Composites use a metal as the matrix (aluminum) strengthened with fibers (silicon carbide). These are often used in the automotive industry [1].

• CMC: Ceramic Matrix Composites use ceramic as matrix and then strengthened by small fibers (silicon carbide and boron nitride) for use in very hot environments [1].

What Are Some Uses of Composite Materials?

General and Industrial Usage

There are many different uses of composite materials. Composites products are used in a variety of different residential and commercial construction. Many parts of a home can be created with plastic laminated beams, which reduces the chances of termite damage. Composite materials can also be used in the aircraft industry. Products like fiberglass, are light enough to fly and  strong enough to handle strong pressures. Another use of composite materials is in the sports industry. Many different sporting goods are made from composite materials, such as a baseball bat. This is to reduce damage and breaking. These materials are also used on products like surfboards to create durability and flexibility. Finally, many boats are made with composite materials such as fiberglass to reduce rot and rust [9].

Use Within Design Teams/For Specialty Pieces

Often, composites are used to create components and structures that require good physical strength with relatively low weight. Student teams often incorporate composite materials in their designs as a result of these positives. However, it is important to note that the bigger the piece, the more factors that would need to be accounted for. Bigger pieces of composites often affect and are affected by other structures and materials it interacts with. Thus, a thorough and elaborate plan is required before starting layups (analysis of smaller samples are recommended).

Selection of Materials

Material selection influences the overall strength, weight, cost, and difficulty of creating the final laminate consolidation. Considerations are made towards the fibre and resin selection, and their interactions with other parts. For example, it is important to note that carbon fiber should never be contacted with aluminium pieces. This is because their similar electrical potential induces possible galvanic corrosion [12].

Considerations For Different Fibres

Fibrous component of composite materials increase the strength and stiffness of the structure depending on the formation method, fiber orientation, weave type, fiber volume fraction, and other factors [1]. Considerations for choosing different fiber types depends on [1]:

1. Mechanical properties of fiber (Tensile, Compressive Strength, Density, etc.)
2. The surface interaction between the fiber and the resin
3. The amount of fiber used in the composite (FVF)
4. Orientation of the fibers  

Carbon Fiber

The majority of carbon fiber is made from the precursor polyacrylonitrile which is heated with no oxygen. Allowing it to burn, and causing the non-carbon atoms to leave structure as atoms vibrate. The result is a polymer composed of long carbon chains [1].

• • • Difference strand thicknesses changes weight and strength.
      • Generally the higher the stronger and thicker
      • 3K, 6K, 12K (3000, 6000, 12000) strands of carbon fiber in each tow of carbon fiber fabric

Fiberglass

Made from some recipe of quarry products (sand, limestone, kaolin, colemanite), then melted at extremely high temperatures. Pushed through small orifices of of 5-24 µm and cooled. Can be drawn together using a thermosetting resin or left apart (rovings) [1].

• • • E-Glass: Electrical Glass
      • Good tensile and compressive strength
      • Extremely resistant to external effects ie. fire, water, acid, alkali, UV
    • C-Glass: Alkali-Lime Glass
      • Provides best resistance to chemical attacks
      • Primarily used in chemical and water pipes
    • R,S,T-Glass: Aluminosilicate, Aluminosilicate without CaO, Thermal Insulator-Glass
      • Highest tensile and compressive strength, with good strength retention
      • 10-20 times  more expensive than E-Glass
      • Primarily used in military vehicles and aerospace

Hybrid/Other

Hybrid composites are two or more types of reinforcements combined into a single fabric, or in different layers of a part. This combination can be for structural or cosmetic reasons, but yield different properties and applications [1].

• • • Carbon Fiber/Kevlar
    • Carbon Fiber/Fiberglass
    • Fiberglass/Kevlar

Considerations For Different Resins

Epoxy

Polyester

Considerations For Different Fiber Orientations

Considerations For Different Fiber Weaves

Considerations For Fiber Volume Fraction (FVF, Vf)

Below are some layup methods that are used to create composite pieces:

Production Methods For Composite Pieces

Hand Layup

The hand lay-up technique is the oldest method of woven composite manufacturing. The materials are prepared by respecting a few different steps. First, the mold surface is treated  by anti adhesive agent to avoid the polymer sticking to the surface. Next, a thin plastic sheet is applied at the top and bottom of the mold plate to get a smooth surface of the product. The layers of the woven reinforcement are cut to required shapes and placed on the surface of the mold. The mats are placed in the preceding polymer layers and pressured using a roller to remove any trapped air bubbles and the excess of polymer as well. The mold is then finally, closed and pressure is released to obtain a single mat. After curing at room temperature, the mold is opened and woven composite is removed from the mold surface [13]. 

Guide: Hand Layup Method Guide.docx

Vacuum Bagging (After Consolidation)

Vacuum bagging is widely used in the composites industry. It is a technique in which one creates a uniform pressure on the surfaces of the objects in a bag. This holds the parts together while the adhesive cures. Pressurizing a composite lamination serves several functions. It removes any trapped air between layers and provides pressure that prevents shifting of fiber orientation during cure. Finally, it also reduces humidity and improves the fiber to resin ratio in the composite part [14].

Guide: Vacuum Bagging Method Guide.docx

Resin Infusion

Resin infusion is the process where the voids in an evacuated stack of porous material are filled with a liquid resin. After the resin solidifies, the solid resin matrix binds the assembly of materials into a unified rigid composite. The reinforcement can be any porous material compatible with the resin. Typical materials include inorganic fibers, organic fibers, or combination of fibers with other materials. The key part of the process is the evacuation, or removal of the air from the porous material prior to admitting the resin [15].

Oven Cured Prepreg

To start off, materials are placed in a bag that has been  successfully leak tested[16]. It can  be put in the oven to cure. The bag is carefully placed in the oven so that it cannot sang or catch on any edges which can cause a puncture. After a vacuum line is connected to the inside of the oven and connected to the pump outside. After the oven doors are closed and the oven is turned on, and a program is used from a laptop or pc [16]. Finally, remove the material.

Comparison of Different Methods Based on Experimental Data

References