Family of Materials
The third learning objective focuses on introducing the various family of materials. Materials are found in all aspects of our lives, from the clothes we wear to the buildings we inhabit. Understanding materials and their families helps us comprehend their properties, uses, and significance in various industries and applications. There are 4 main families of materials: Metals, Polymers, Ceramics, and Composites. Each of these materials will be discussed along with their properties and uses.
METALS
Metals are a class of materials characterized by their excellent conductivity, strength, and malleability. They are widely used in engineering and everyday applications due to their versatility and durability. In terms of their properties and appearances, metals differ from each other yet share many qualities; let’s break down the main properties of metals:
Conductivity
Metals are great conductors of both electricity and heat. This means that they allow electricity and heat to flow through them easily. That’s why we use metals in electrical wires, where we need electricity to travel from one place to another, and in cooking pots, where we want heat to spread evenly.
Density
Metals are quite dense, which means they have a lot of mass packed into a small space. This density gives metals their weightiness. When you hold a metal object, you can feel its heft compared to other materials like plastic or wood.
Malleability and Ductility
Metals are very bendy and stretchy compared to other materials. We say they’re malleable and ductile. This means you can shape them into different forms without breaking them. Think about how you can hammer a piece of metal into a thin sheet, like aluminum foil, or pull it into a wire, like the wire in your headphones.
High Melting/Boiling Point
Metals usually have high melting and boiling points. The atoms in metals are closely packed. So, more energy is required to break the metallic bonding between the atoms. This also explains why metals are solid at room temperature which does not provide the energy required to break the strong metallic bond to convert the solid to a liquid state.
Strength
Metals are usually strong and sturdy. They can support heavy loads and withstand a lot of force without breaking. That’s why we use metals in construction for building structures like bridges and skyscrapers, and in making tools and machinery that need to be tough.
Shiny Appearance
Most metals have a shiny or metallic luster, where luster describes the visual appearance of a material based on how it reflects light. Think about how a silver spoon reflects light or how a gold necklace sparkles.
The most common types of metals found in everyday objects are:
POLYMERS
Polymers are found everywhere around you, from the rubber in your tires to plastic bags and water bottles to the nylon in your clothes. But what are they made of to have this wide range of products?
By definition, polymers are large molecules made by bonding a series of building blocks. These building blocks, called monomers, determine the polymers’ characteristics such as their physical and mechanical properties, chemical structure, etc. Think of a polymer as a chain or a branch, with each of its links a monomer. Those monomers can be simple — just an atom or two or three — or they might be complicated ring-shaped structures containing a dozen or more atoms.
The main properties of polymers include:
Insulation
Polymers are often good insulators, which means they don’t conduct electricity or heat very well. This property makes them useful for things like electrical wiring, where you want to keep the electricity contained within the wire and not let it leak out.
Strength
Despite being flexible, polymers can also be very strong. When the chains of molecules are tightly packed together, they can resist being pulled apart or broken. This strength makes polymers useful for making things like plastic bottles, which need to hold liquids without leaking.
Versatility
A unique ability of polymers is that they can be customized to have different properties. By changing the types of molecules used or how they’re linked together, scientists can create polymers with specific characteristics. This versatility allows us to make all kinds of different materials, from soft and squishy rubber to hard and durable plastic.
Lightweight
Many polymers are lightweight, which means they don’t weigh very much for their size. This makes them great for things like backpacks and water bottles, where you want something that’s easy to carry around.
Flexibility
Polymers are made of long chains of molecules making them naturally very flexible, similar to stretching a rubber band or bending a plastic straw. This flexibility comes from the ability of polymer chains to move and slide past each other.
Durability
Many polymers are resistant to chemicals, corrosion, and environmental factors such as moisture and UV radiation. This durability contributes to their longevity in various applications.
The most common types of polymers are:
CERAMICS
Ceramics are encountered in your everyday life, from dishes and tiles to electronic devices and even spacecraft components. They are non-metallic materials typically made from inorganic compounds like clay, sand, or alumina (aluminum oxide) that are mixed with water to form a paste that can be molded and shaped into any desired form, then heated to harden. There are several types of ceramics, the two main types are:
Some of the main properties of ceramics include:
Insulation
Ceramics are typically poor conductors of heat and electricity. This makes them useful for applications where insulation is needed, such as electrical insulators, thermal barriers, and protective coatings.
Brittleness
While ceramics are known for their hardness, it comes at the price of their brittleness, meaning they’re prone to breaking or cracking under stress. This is because the bonds between the particles are rigid and inflexible. So, while ceramics are great for dishes and tiles, you wouldn’t want to drop them on a hard surface!
Hardness
Ceramics are known for their hardness and rigidity. Once they’re heated, the particles inside them bond tightly together, forming a solid structure that’s difficult to break. This hardness makes ceramics suitable for a wide range of applications, from dishes and tiles to industrial machinery components.
Heat Resistant
Ceramics can withstand high temperatures without melting or deforming. This property makes them ideal for use in situations where heat resistance is important, such as ovenware, and spacecraft heat shields.
The most common types of ceramics are:
• Earthenware: Earthenware ceramics are made from clay and other natural materials. It is commonly used for pottery and decorative items due to its porous nature making it brittle.
• Stoneware: Stoneware ceramics are fired at higher temperatures than earthenware, resulting in a denser and less porous material. It is durable and often used for tableware, kitchenware, and decorative pieces.
• Porcelain (China): Porcelain is made from higher-grade clay and other minerals and is fired at higher temperatures than other ceramics. It is strong, dense, and non-porous, making it ideal for tableware, bathroom tiles, and decorative objects.
• Oxide Ceramics: Oxide ceramics include materials like alumina (aluminum oxide) and zirconia (zirconium oxide). They are extremely hard, resistant to heat and corrosion, and are used in cutting tools, automotive components, and medical implants.
• Carbide Ceramics: Carbide ceramics are very hard and have excellent wear resistance. Silicon carbide and tungsten carbide are used in cutting tools, abrasives, and industrial machinery parts.
• Nitride Ceramics: Nitride ceramics offer high strength, thermal conductivity, and resistance to chemical attack. Silicon nitride and aluminum nitride are used in aerospace, electronics, and semiconductor applications.
COMPOSITES
Composites are made by mixing together two or more materials that have different properties. One of these materials is usually a strong, reinforcing component, while the other is a matrix that holds everything together. When combined, these materials create a new composite material with unique properties. Imagine making a sandwich where each layer contributes something different, like flavor or texture.
In composites, like carbon fiber reinforced polymers (CFRP), two main components work together: the reinforcement and the matrix. The reinforcement is like the “skeleton” of the composite and is typically made of strong fibers such as carbon, fiberglass, or Kevlar. These fibers provide the composite with its strength and stiffness, similar to how steel bars reinforce concrete to make it stronger.
The matrix is the “glue” that holds everything together. It surrounds and supports the reinforcement fibers, keeping them in place and transferring loads between them. The matrix can be made of materials like epoxy resin, which is durable and lightweight. It protects the fibers from damage, prevents them from moving around, and helps distribute stresses throughout the composite.
Together, the reinforcement and matrix create a composite material that is lightweight yet incredibly strong. The reinforcement fibers provide the strength and stiffness, while the matrix keeps everything organized and ensures the composite can withstand different types of forces. This combination of components allows composites to be used in industries like aerospace, automotive, and sports, where high-performance materials are needed.
Stiffness is defined as the “springiness” or resistance of an object to bending or stretching. Picture a brand-new pencil versus a rubber band. The pencil is stiff because it doesn’t bend easily when you try to flex it, like a sturdy tree branch. On the other hand, the rubber band is not stiff; it stretches easily when you pull it. So, stiffness is like how “rigid” or “bendy” something feels. When we talk about materials being stiff, it means they resist bending and remain strong and solid.
The main properties of composites are:
High Strength and Stiffness
Composites achieve high strength and stiffness by combining strong fibers, like carbon or fiberglass, with a supportive matrix material, such as epoxy resin. When forces are applied, the fibers distribute and bear the load throughout the material, providing exceptional strength. The matrix holds the fibers in place, enhancing stiffness and protecting against damage. This combination results in lightweight materials with superior strength, ideal for applications in aerospace, automotive, and sports equipment.
Fatigue Life
Composites have good fatigue life because of their unique structure that combines strong fibers with a supportive matrix. When materials undergo repetitive loading or stress over time, they can weaken and eventually fail due to fatigue. In composites, the fibers distribute the load and prevent the formation of microcracks that can lead to failure. The matrix helps to protect the fibers and distribute stress, enhancing durability against fatigue. This combination allows composites to withstand repeated stress and loading cycles without losing their strength, making them ideal for applications requiring long-lasting and reliable performance, such as in aerospace, automotive, and sports equipment.
Tailored Design
Composites have tailored design capabilities because engineers can customize them by combining different materials in specific ways to achieve desired properties. By varying the type, orientation, and amount of fibers used, along with the choice of matrix material, composites can be optimized for strength, stiffness, and weight. This flexibility in design allows composites to be tailored for specific applications, such as lightweight aircraft components or strong sports equipment, by carefully selecting and arranging materials to meet specific engineering requirements.
Corrosion Resistance
Composites have corrosion resistance because they are made with materials that do not react with water or chemicals. For instance, fiberglass reinforced plastics (FRP) use fiberglass and polymer resin, which are naturally resistant to corrosion. Unlike metals that can rust or degrade, composites stay stable and strong in marine and chemical environments, making them durable choices for various applications.
The most common types of composites are:
Quiz!
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GOODLUCK!
DONE!
Congratulations on completing the materials section! By mastering the fundamentals of materials, you’ve taken the first step towards becoming a skilled mechanical engineer. Stay curious, keep exploring, and continue building your knowledge of this exciting field!