122.2.4 - Statics & Strengths

Composites

What are "Composites"?

Composites are materials made from two or more different materials with distinct physical or chemical properties. When combined, they produce a material with characteristics different from the individual components.
The primary objective of creating composites is to derive synergistic benefits from the combination, where the new material has enhanced or more desirable properties than the individual constituents.
Materials used to make up composites are one of two things: matrix or reinforcement
- A Reinforcement material enhances certain specific properties of the matrix material. This could be increasing strength, rigidity, toughness, or altering other attributes like thermal conductivity or electrical conductivity.
- A Matrix binds the reinforcement together, distributing loads and stresses across the composite material. It also protects the reinforcement from environmental factors like moisture, UV radiation, and chemical attack. Without the matrix, the reinforcement could be vulnerable to degradation or damage.
Common examples of composites used throughout the world include:
- Concrete, which is aggregate reinforcement in a cement matrix

Composite Reinforcements

Reinforcements can come in many different materials/shapes/forms/patterns, all of which can greatly affect the properties of the composite
One of the most common composite reinforcements is a category of materials called Fibers
- Fibers are slender, elongated structures or materials that are often significantly longer than they are wide. This unique geometry gives them a range of properties, such as flexibility, tensility, and the ability to be woven or spun into larger structures like yarns or fabrics.
  - Because of this, Fiber-Reinforced Composites (FRCs) are perhaps the most widely-recognized and used category within the composites industry
- Commonly-used types of Fibers include:
  - Glass Fibers. The most commonly used fibers in composites due to their strength, flexibility, and resistance to chemicals. They are often seen in automotive, marine, and construction applications.
  - Carbon Fibers. Known for their high strength-to-weight ratio and stiffness. They are used in high-performance applications such as aerospace, high-end automotive, and sports equipment.
  - Aramid Fibers. Renowned for their toughness and are used in applications requiring impact or abrasion resistance, like bulletproof vests (e.g. Kevlar).
  - Natural Fibers. Sustainable alternatives, which are often used in less critical applications where biodegradability is a priority (e.g. Jute, Hemp, Flax).

Directionality of reinforcement within a composite can translate to directionality of material properties
- Materials which properties are uniform in all directions are Isotropic
- Materials which properties vary based on direction are Anisotropic
For example, a composite with fibers aligned in one direction will exhibit maximum strength along that axis, but may be less robust in other directions.
- This principle allows engineers to tailor composites for specific applications, optimizing for strength, conductivity, or other attributes as required.
- However, it also introduces challenges, as properties like strength may vary depending on the direction of applied forces.
Essentially, by controlling reinforcement directionality, designers can customize the performance characteristics of a composite material to suit specific needs.

Composite Matrices

Synthetic Polymer Matrix Composites (SPMCs)

SPMCs are built upon matrices made from man-made polymers, such as epoxy, polyester, or nylon. Often reinforced with glass, carbon, or aramid fibers, they dominate various industries due to their versatility, lightweight nature, and tailorability. Common applications range from automotive to aerospace sectors. While offering a wide range of mechanical and thermal properties, concerns about their environmental impact, especially end-of-life recyclability and disposal, persist. In essence, SPMCs provide a vast range of customizable properties, but their environmental footprint necessitates ongoing research into sustainable practices.
Examples include:
- Glass Fiber-Reinforced Polymer (GFRP): Used in boat hulls, automotive panels, and wind turbine blades.
- Carbon Fiber-Reinforced Polymer (CFRP): Essential for high-performance applications like aerospace components, racing car bodies, and some sporting goods like tennis rackets and bicycles.
- Aramid Fiber-Reinforced Polymer (often known by the brand name Kevlar): Found in bulletproof vests, protective helmets, and ropes.

Natural Polymer Matrix Composites (NPMCs)

Natural Polymer Matrix Composites (NPMCs) utilize matrices derived from naturally occurring polymers like cellulose, starch, or proteins. Common examples include cellulose-based composites reinforced with natural fibers like flax or hemp, and starch-based composites that can incorporate various reinforcements. These composites are prized for their sustainability and biodegradability, originating from renewable sources and often degrading without releasing toxins. However, they might face challenges in consistent performance and durability compared to synthetic counterparts. Essentially, NPMCs represent a balance between environmental responsibility and material performance.
Examples include:
- Cellulose-based Composites: Often seen in biodegradable packaging materials and some automotive parts.
- Starch-based Composites: Utilized in bioplastics and some disposable cutlery.
- Protein-based Composites: Found in some adhesives and coatings, and occasionally in research contexts for biomedical applications.

Ceramic Matrix Composites (CMCs)

CMCs utilize a ceramic material, such as alumina, silicon carbide, or carbon, as the matrix. With the ability to maintain strength at high temperatures and resist corrosion, they're especially relevant in aerospace and industrial applications where thermal stability is crucial. However, they tend to be more brittle than other composite types. The key advantage of CMCs is their performance under extreme conditions, but addressing their brittleness remains a challenge for many applications.
Examples include:
- Silicon Carbide (SiC) Reinforced with Carbon: Utilized in high-performance brake discs.
- Alumina Matrix with Silicon Carbide Fibers: Used in aerospace applications for its resistance to high temperatures.
- Carbon-Carbon Composites: Found in aerospace applications such as heat shields and braking systems due to their ability to maintain properties at extreme temperatures.

Metal Matrix Composites (MMCs)

MMCs integrate a metal, like aluminum, titanium, or magnesium, as the matrix material. By combining the ductility and strength of metals with the stiffness of reinforcements, they offer a blend of properties ideal for automotive, aerospace, and electronics. They efficiently dissipate heat and possess good wear resistance. However, their production can be complex and costly. In summary, MMCs merge the best of metals and reinforcements, but their fabrication often requires sophisticated techniques and resources.
Examples include:
- Aluminum reinforced with Silicon Carbide (Al/SiC): Common in automotive brake rotors for enhanced wear resistance.
- Titanium reinforced with Carbon Fibers: Utilized in some aerospace applications to achieve a balance between weight and strength.
- Magnesium reinforced with Ceramic Particles: Found in automotive applications to reduce weight without compromising strength.

2.4✔ CHECKPOINT

ID Composites

In the lab, correctly distinguish and identify at least one example of components made from the following composites, being used as a functional component on a piece of equipment (do NOT disassemble or damage any components/equipment):
- Synthetic Polymer Matrix Composite
- Ceramic Matrix Composite
- Metal Matrix Composite
Document and analyze all your examples:
- Provide evidence/reasoning/proof the component is made of what you think it is
- Determine, understand, and explain why the particular composite in question was chosen for each component (properties, cost, etc.)

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