Classification of Engineering Materials

In this video we're going to introduce five different classifications of engineering materials and we're going to discuss those briefly just so that we know how to classify different engineering materials into one of each of these classifications. We're then going to talk about some of the properties that relate to each of these classifications of material. So what we have here is we have five different classes of material. We have metals, ceramics, polymers, composites and advanced materials. Now for the purpose of this video we're only going to look at the first four, metals, ceramics, polymers and composites. So most of us are familiar with different types of metals but what we probably haven't thought about is what those particular metals are made up of. So first of all we have metallic elements and metallic elements appear on the periodic table. They're essentially pure metals. We think of things such as copper, aluminium, iron, titanium, even silver and gold. Those are all examples of metallic elements because those are pure metals. But what we can also have is something called metal alloys. And metal alloys are mixtures of different materials. Sometimes it's a mixture of a metal and a non-metal and other times it's a mixture of two metals. And I'll give you some examples. Brass is a combination of copper, which is a metallic element, and zinc, which is also a metallic element. Those two metallic elements are mixed in order to produce the alloy brass. Another example is bronze which is a mixture of copper and tin which are both metals. But we can also have alloys of metals and non-metals and the most common example would be steel which is made primarily of iron but also contains carbon. The important thing with alloys is those materials aren't bonded together. They're mixed but they're not chemically bonded as we'll see in later videos. The other thing to consider when we talk about metals is the difference between a ferrous and a non-ferrous metal. So ferrous metals always contain iron. So examples of ferrous metals would be cast iron, steel, which is a mixture of iron and carbon, but also things like stainless steel. Anything that contains iron is considered to be a ferrous metal. On the other hand, we have non-ferrous metals, and these can be pure metals such as copper, aluminium and tin, or they can also be metal alloys. such as brass and bronze. The important thing here is whether they contain iron or whether they don't contain iron. Ferrous contains iron, non-ferrous doesn't contain iron. So next we have our ceramics and ceramics are often classified as oxides, nitrides and carbides. None of these are elements because they're all combinations of different materials, this time chemically bonded together. So if we take the example of silicon oxide. Now where you would have seen silicon oxide is in glass. And common glass is made up of roughly 75% silicon oxide. It's a ceramic material. Next we have nitrides and a good example of a ceramic nitride is silicon nitride. And these can be used for functions such as bearings and so on. Where we have two surfaces which are rubbing together and what we don't want is for one surface to wear the other surface. And finally we have carbides and a typical application of something like silicon carbide would be for grinding discs in an angle grinder. Again a very hard material, a combination there of silicon and carbon. Our next classification of engineering material is polymers. Now in layman's terms polymers are often referred to as plastics. So a plastic drinking bottle is actually a bottle made of a polymer. Plastic is the incorrect term in terms of engineering materials because plasticity refers to a property. And we know already that it's the property where a material deforms and doesn't return to its original state. So when we talk about things commonly made of plastics, what we actually need to refer to now as engineers is things being made of polymers or polymer materials. Now, typically, polymers are made up of chains of hydrocarbons. And hydrocarbons are simply just hydrogen and carbon atoms that are bonded together into long chains. And again, we'll see this in a later tutorial. But we have two key classifications of polymers. We have thermoplastics and we have thermosetting plastics. Now, the big difference here is whether they can be remelted once they've been formed. Now, thermoplastics can. So a thermoplastic can typically be recycled. Let's refer back to our drinking bottle. We know that the drinking bottle can be recycled. That means it can be heated, it can be melted and it can be reformed. It must be a thermoplastic. But thermosetting plastics, once they've been formed, because of the chemical reactions that take place, they can no longer be melted. We can apply heat to them and they'll char, but they won't melt. And a good example of where thermosetting plastics is used is in the front fascias of electrical sockets. So if you were to take the front fascia of an electrical socket and apply heat and try and melt that, it wouldn't actually melt, it would just char. Really what that means is that it couldn't be recycled. The bonding is too strong once it's been chemically formed. Now the final classifications of materials that we're going to look at are composite materials. And a composite really just means the combination of two or more materials. And what composite materials do is they actually combine the properties of the two parent materials. And we'll take a look at some examples in a moment. So there we have our five classifications of engineering materials. Advanced materials are actually beyond the scope of this video. But what we're often interested in is the properties of each of these classifications of materials. So what properties does the group metals tend to share? And what properties does the group ceramics tend to share? And we're going to look at that now. So some of the general properties of metals, and I want to make this clear, these are the general properties. Because different metals have different properties we can alloy metals which changes the properties but in general metals tend to have low elasticity or high stiffness. Now what that means is when we apply forces to them they tend to be resistant to deformation or certainly elastic deformation. So if we were to place a metal under tension then The amount of elastic deformation that it undergoes is going to be less than something like a polymer. That doesn't mean to say that it won't plastically deform, but what it does mean is that at relatively low stress levels the amount of elastic deformation when compared to other materials is relatively low. They tend to have high strength, so they tend to be resistant to high forces in tension and compression. Another thing that's important about metals is that they tend to be malleable and ductile, meaning that they can be shaped and formed. And here we're talking about permanent deformation or plastic deformation. Now here it is important to note that when we alloy metals, particularly things like high carbon steel and various different bronze alloys, is in fact that property may change. So it's not fixed and rigid, there is a certain amount of flexibility here when we start to alloy metals. Also metals tend to have high density. They tend to be heavy in relation to their volume. And when we start to look at the structure of engineering materials we'll see that that's because the atoms are very tightly packed. Some of the other things that you would expect from a metal is that they're good conductors of heat and electricity and we'll look at some of the reasons behind that again in a later video. And finally the majority, and again this isn't in all cases, but the majority of metals have high magnetic permeability meaning they can be magnetised. If we think of our ceramics, ceramics are similar to metals in that they have low elasticity and high strength. So that's common to the two groups of material. Where they differ is that ceramics are very hard. They're very resistant to scratching and indentation. But the flip side of that or the downside of that is that they can be very brittle as well. Therefore, sudden or impact forces on ceramics tend to cause them to fracture. If we think of glass as a prime example there, it's very hard to scratch but it's also very brittle. Now ceramics also tend to have high melting points, meaning the temperature required to turn them into liquids is very high. And in contrast to metals, they actually have very low heat and electrical conductivity. They're what we would classify as insulators of heat and electricity. So moving on to our polymers, in contrast to both metals and ceramics they tend to have high elasticity and low strength meaning they stretch a lot under forces and they're not able to withstand the high forces that our metals and our ceramics are able to. Now this is partly because they're low density and low weight materials. So I have put in brackets there that when we talk about the strength of a polymer what we're really referring to is its absolute strength rather than its strength compared to its weight. But in general terms they have low strength and low density. They also have comparatively low melting points, meaning the temperature required to turn them to liquid is much less. And they're also insulators of both electricity and heat. This is the reason why when we have electrical cables, we often put a polymer shroud around them so that people don't get electrocuted when they touch those cables. And the same is true for heat because electrical wires become hot when they pass electricity. By putting an insulator on the outside it actually prevents the heat from transferring through that boundary as well. Now something we haven't really mentioned but which is common to polymers is that they're highly unreactive. They don't tend to oxidize like various different metals do so they're resistant to environmental factors. And finally we have our composites. Now for composites, as I mentioned, these are combinations of different materials. So it's very difficult to assign general properties to this group. So instead I've given some examples of composites. Now one example of a composite material is reinforced concrete. And reinforced concrete is similar to normal concrete, except it would have steel reinforcement running through. So combining those two materials together, each of those parent materials bring their strengths or bring their properties to the composite. So we end up with a resulting composite with high tensile and compressive strength. The next two then are GFRP or glass fibre reinforced polymer and CFRP carbon fibre reinforced polymer. The glass fibre reinforced polymer is basically a plastic with glass fibres running through, or we can think of it the other way glass fibres encased in a polymer. And carbon fibre reinforced polymer is the same except this time we have carbon fibres running through the material. Now the huge benefit of both of these types of material is their strength to weight ratio. As we've said previously polymers tend to be very light but they tend to lack strength. They can also be formed into lots of complex shapes. Now by reinforcing them with a material with a high tensile strength we're able to produce a composite material that's very light and very strong and it'll also be resistant to various different environmental factors. The third example I've got there is Kevlar composite which is used for body armour and armoured vehicles. Again it's very light, it's very strong but it's also resistant to piercing and penetration and that's largely because the Kevlar fibres are very hard and it's very difficult to cut. So in a Kevlar composite the Kevlar which is a synthetic material will be weaved to produce a mesh and then that will be encased in a polymer providing a material that's very much resistant to knife attacks, bullets and other projectiles. So in this video we've introduced our five classifications of materials, metals, ceramics, polymers, composites and advanced materials, and we've also talked about the general properties that relate to each of those classifications of materials. As we work through this learning outcome we will introduce things such as chemical bonding and structures of materials so that we can begin to understand why these different classifications of materials tend to share the properties of other materials in the same class.

We have metals, ceramics, polymers, composites and advanced materials. Now for the purpose of this video we're only going to look at the first four, metals, ceramics, polymers and composites. So most of us are familiar with different types of metals but what we probably haven't thought about is what those particular metals are made up of. So first of all we have metallic elements and metallic elements appear on the periodic table.

They're essentially pure metals. We think of things such as copper, aluminium, iron, titanium, even silver and gold. Those are all examples of metallic elements because those are pure metals. But what we can also have is something called metal alloys.

And metal alloys are mixtures of different materials. Sometimes it's a mixture of a metal and a non-metal and other times it's a mixture of two metals. And I'll give you some examples.

Brass is a combination of copper, which is a metallic element, and zinc, which is also a metallic element. Those two metallic elements are mixed in order to produce the alloy brass. Another example is bronze which is a mixture of copper and tin which are both metals. But we can also have alloys of metals and non-metals and the most common example would be steel which is made primarily of iron but also contains carbon.

The important thing with alloys is those materials aren't bonded together. They're mixed but they're not chemically bonded as we'll see in later videos. The other thing to consider when we talk about metals is the difference between a ferrous and a non-ferrous metal. So ferrous metals always contain iron. So examples of ferrous metals would be cast iron, steel, which is a mixture of iron and carbon, but also things like stainless steel.

Anything that contains iron is considered to be a ferrous metal. On the other hand, we have non-ferrous metals, and these can be pure metals such as copper, aluminium and tin, or they can also be metal alloys. such as brass and bronze.

The important thing here is whether they contain iron or whether they don't contain iron. Ferrous contains iron, non-ferrous doesn't contain iron. So next we have our ceramics and ceramics are often classified as oxides, nitrides and carbides. None of these are elements because they're all combinations of different materials, this time chemically bonded together.

So if we take the example of silicon oxide. Now where you would have seen silicon oxide is in glass. And common glass is made up of roughly 75% silicon oxide. It's a ceramic material. Next we have nitrides and a good example of a ceramic nitride is silicon nitride.

And these can be used for functions such as bearings and so on. Where we have two surfaces which are rubbing together and what we don't want is for one surface to wear the other surface. And finally we have carbides and a typical application of something like silicon carbide would be for grinding discs in an angle grinder. Again a very hard material, a combination there of silicon and carbon. Our next classification of engineering material is polymers.

Now in layman's terms polymers are often referred to as plastics. So a plastic drinking bottle is actually a bottle made of a polymer. Plastic is the incorrect term in terms of engineering materials because plasticity refers to a property. And we know already that it's the property where a material deforms and doesn't return to its original state.

So when we talk about things commonly made of plastics, what we actually need to refer to now as engineers is things being made of polymers or polymer materials. Now, typically, polymers are made up of chains of hydrocarbons. And hydrocarbons are simply just hydrogen and carbon atoms that are bonded together into long chains.

And again, we'll see this in a later tutorial. But we have two key classifications of polymers. We have thermoplastics and we have thermosetting plastics. Now, the big difference here is whether they can be remelted once they've been formed. Now, thermoplastics can.

So a thermoplastic can typically be recycled. Let's refer back to our drinking bottle. We know that the drinking bottle can be recycled. That means it can be heated, it can be melted and it can be reformed. It must be a thermoplastic.

But thermosetting plastics, once they've been formed, because of the chemical reactions that take place, they can no longer be melted. We can apply heat to them and they'll char, but they won't melt. And a good example of where thermosetting plastics is used is in the front fascias of electrical sockets.

So if you were to take the front fascia of an electrical socket and apply heat and try and melt that, it wouldn't actually melt, it would just char. Really what that means is that it couldn't be recycled. The bonding is too strong once it's been chemically formed.

Now the final classifications of materials that we're going to look at are composite materials. And a composite really just means the combination of two or more materials. And what composite materials do is they actually combine the properties of the two parent materials.

And we'll take a look at some examples in a moment. So there we have our five classifications of engineering materials. Advanced materials are actually beyond the scope of this video. But what we're often interested in is the properties of each of these classifications of materials.

So what properties does the group metals tend to share? And what properties does the group ceramics tend to share? And we're going to look at that now.

So some of the general properties of metals, and I want to make this clear, these are the general properties. Because different metals have different properties we can alloy metals which changes the properties but in general metals tend to have low elasticity or high stiffness. Now what that means is when we apply forces to them they tend to be resistant to deformation or certainly elastic deformation.

So if we were to place a metal under tension then The amount of elastic deformation that it undergoes is going to be less than something like a polymer. That doesn't mean to say that it won't plastically deform, but what it does mean is that at relatively low stress levels the amount of elastic deformation when compared to other materials is relatively low. They tend to have high strength, so they tend to be resistant to high forces in tension and compression.

Another thing that's important about metals is that they tend to be malleable and ductile, meaning that they can be shaped and formed. And here we're talking about permanent deformation or plastic deformation. Now here it is important to note that when we alloy metals, particularly things like high carbon steel and various different bronze alloys, is in fact that property may change. So it's not fixed and rigid, there is a certain amount of flexibility here when we start to alloy metals.

Also metals tend to have high density. They tend to be heavy in relation to their volume. And when we start to look at the structure of engineering materials we'll see that that's because the atoms are very tightly packed. Some of the other things that you would expect from a metal is that they're good conductors of heat and electricity and we'll look at some of the reasons behind that again in a later video.

And finally the majority, and again this isn't in all cases, but the majority of metals have high magnetic permeability meaning they can be magnetised. If we think of our ceramics, ceramics are similar to metals in that they have low elasticity and high strength. So that's common to the two groups of material.

Where they differ is that ceramics are very hard. They're very resistant to scratching and indentation. But the flip side of that or the downside of that is that they can be very brittle as well. Therefore, sudden or impact forces on ceramics tend to cause them to fracture.

If we think of glass as a prime example there, it's very hard to scratch but it's also very brittle. Now ceramics also tend to have high melting points, meaning the temperature required to turn them into liquids is very high. And in contrast to metals, they actually have very low heat and electrical conductivity.

They're what we would classify as insulators of heat and electricity. So moving on to our polymers, in contrast to both metals and ceramics they tend to have high elasticity and low strength meaning they stretch a lot under forces and they're not able to withstand the high forces that our metals and our ceramics are able to. Now this is partly because they're low density and low weight materials.

So I have put in brackets there that when we talk about the strength of a polymer what we're really referring to is its absolute strength rather than its strength compared to its weight. But in general terms they have low strength and low density. They also have comparatively low melting points, meaning the temperature required to turn them to liquid is much less. And they're also insulators of both electricity and heat. This is the reason why when we have electrical cables, we often put a polymer shroud around them so that people don't get electrocuted when they touch those cables.

And the same is true for heat because electrical wires become hot when they pass electricity. By putting an insulator on the outside it actually prevents the heat from transferring through that boundary as well. Now something we haven't really mentioned but which is common to polymers is that they're highly unreactive. They don't tend to oxidize like various different metals do so they're resistant to environmental factors. And finally we have our composites.

Now for composites, as I mentioned, these are combinations of different materials. So it's very difficult to assign general properties to this group. So instead I've given some examples of composites.

Now one example of a composite material is reinforced concrete. And reinforced concrete is similar to normal concrete, except it would have steel reinforcement running through. So combining those two materials together, each of those parent materials bring their strengths or bring their properties to the composite.

So we end up with a resulting composite with high tensile and compressive strength. The next two then are GFRP or glass fibre reinforced polymer and CFRP carbon fibre reinforced polymer. The glass fibre reinforced polymer is basically a plastic with glass fibres running through, or we can think of it the other way glass fibres encased in a polymer. And carbon fibre reinforced polymer is the same except this time we have carbon fibres running through the material. Now the huge benefit of both of these types of material is their strength to weight ratio.

As we've said previously polymers tend to be very light but they tend to lack strength. They can also be formed into lots of complex shapes. Now by reinforcing them with a material with a high tensile strength we're able to produce a composite material that's very light and very strong and it'll also be resistant to various different environmental factors. The third example I've got there is Kevlar composite which is used for body armour and armoured vehicles. Again it's very light, it's very strong but it's also resistant to piercing and penetration and that's largely because the Kevlar fibres are very hard and it's very difficult to cut.

So in a Kevlar composite the Kevlar which is a synthetic material will be weaved to produce a mesh and then that will be encased in a polymer providing a material that's very much resistant to knife attacks, bullets and other projectiles. So in this video we've introduced our five classifications of materials, metals, ceramics, polymers, composites and advanced materials, and we've also talked about the general properties that relate to each of those classifications of materials. As we work through this learning outcome we will introduce things such as chemical bonding and structures of materials so that we can begin to understand why these different classifications of materials tend to share the properties of other materials in the same class.

Transcript for:Classification of Engineering Materials

Transcript for:
Classification of Engineering Materials