Lesson video

Hi there, everyone, my name's Mr. Booth, and welcome to your Design & Technology lesson for today.

It's fantastic that you could join me.

Today, we are gonna be testing the working properties of materials with a focus on hardness.

It's really important that we can test working properties because of course, if we're gonna select materials based on those working properties, we've gotta have some firsthand knowledge of how materials perform.

This is part of the "Materials testing" unit.

Today's outcome, I want you to be able to test the working properties of materials, and again, we're gonna focus on hardness.

Four keywords for today that are all related.

The first one is hardness, the ability of a material to resist scratching and indentation.

Now, to carry out a hardness test, we're gonna need an indenter.

That's our next keyword.

This is a tool or object pressed into a material's surface during a hardness test.

Now, in industry, there are a number of ways of testing hardness, but two of the most common tests that are done are the Vickers and the Brinell test.

So Vickers is our next keyword, an industrial hardness test that uses a diamond-shaped pyramid indenter.

And then we have the Brinell test, an industrial hardness test that uses a steel or tungsten carbide ball indenter.

So let's have a look at some of these tests.

Two learning cycles.

The first is all about industrial hardness testing, and then we're gonna do some workshop hardness testing as well.

So let's have a look at how they do this in industry.

Now, material hardness is the ability of a material to withstand scratching and indentation.

Knowing how hard a material is helps designers and engineers to select the correct material for a product.

Hard materials are used for products such as cutting tools.

That's one of the products that we can think about.

Now, if you think about the function of a cutting tool, its job is to cut through other materials, so it needs to be hard.

So that's a fantastic product to think about when you are considering hardness.

Now, hardness tests are conducted for lots of reasons.

They are conducted for quality control purposes to make sure your materials are as hard as you think they are.

You can also get a general understanding of a material's working properties from conducting hardness tests.

You might have also carried out some heat treatment of a product.

So hardness testing can actually test that heat treatment to make sure it is at the standard that you require.

Now, hardness tests, they're quick, they're inexpensive, and also, they're not as destructive as other working property tests, such as tensile testing.

You can sometimes even test final products using this because the indentation is so small.

Quick check for understanding.

True or false? Hardness testing is a form of quality control.

Is that true or is that false? Pause the video now, have a go at this, and come back to me when you've got your answer.

It is, of course, true.

But do you know why? Can you tell me why? Think of an answer, pause the video, and come back to me when you've got that.

Well, it is, of course, yes, they're quick, they're inexpensive, and they're used for quality control on products and product surfaces.

Well done.

Now, there are two forms of industrial methods for testing hardness.

These are Vickers and Brinell tests.

There is actually another one, but we're not gonna focus on that one in today's lesson.

So the Vickers test is a highly accurate and precise test for smaller material samples, where the Brinell test is often used for non-uniform materials surfaces, such as if you want to test a casting.

Quick check for understanding.

What is the correct definition of material hardness? Is it A, a material's ability to resist bending? Is it B, a material's ability to resist being drawn out? C, a material's ability to resist scratching and indentation? Or D, a material's ability to resist impact without breaking? Pause the video now, have a go at this, and come back to me when you've got the correct definition.

It is, of course, C, a material's ability to resist scratching and indentation.

Well done.

Let's have a closer look at the Vickers hardness test.

So first of all, the test piece surface needs to be prepared.

So it's cleaned so it's free from dirt and grease, and that's so we can get an accurate test and an accurate measurement.

There's our indenter, and there's our test piece, and they are about to meet.

A small diamond-shaped pyramid indenter is pressed into the material's surface.

And it's pressed into the surface under a specific load and for a specific time, and that's to ensure consistency and to make sure when we're testing different materials, it is a fair test.

And you can see there the load is applied.

The load is slowly removed, and that's also really important.

The material now has an impression from the indenter.

Now, the harder the material, the smaller the indentation will be.

And you can see the load is removed there.

And there's our indent you can see in the surface of the material.

And there's our test piece.

Now, if we look at our test piece from above, the diagonal of the indentation are measured, and the Vickers hardness number can now be calculated.

So there's our test piece, and we're looking at it from above now.

There's our indent from above, so you can see the pyramid shape if you imagine looking at a pyramid from above.

And then what we do is we measure the diagonals, and that will give us our Vickers hardness number.

Quick check for understanding.

We've just conducted a Vickers hardness test on these three materials.

This is looking at the materials from above, and this is looking at the indentation.

Which of these materials is the hardest? Is it A, B, or C? Pause the video now, have a go at this, and come back to me when you've got your answer.

It is, of course, B because that's got the smallest indent.

And remember that all of these materials will have had the same load and for the same time.

Now let's look at the Brinell hardness test.

So it's very similar.

The test piece surface is obviously cleaned and prepared again, so make sure there's no dirt or grease so we get a nice clean surface so we can take an accurate reading.

Our indenter you can see is a slightly different shape.

This time, it is a ball, but our test piece is exactly the same.

The hardened steel ball indenter is pressed into the material's surface once again for a specific load for a specific time to ensure consistency across different materials.

The load is slowly removed.

The material now has an impression from the indenter.

And once again, the harder the material, the smaller the indentation.

There's our indent; there's our test piece.

Once again, looking at our test piece from above, the diameter of the indentation is measured, and the Brinell hardness number can then be calculated.

So we look there, you can see the diameter across the circle of the indentation.

Quick check for understanding.

What shape indenter is used during the Brinell hardness test? So imagine you're looking down on the test piece here.

Which of those would you say is the Brinell hardness test? Pause the video now, have a go at this, and come back to me when you've answered.

It is, of course, A because it uses a ball, so we're going to see a circle.

Well done.

Now, both tests use a specific load applied for a specific time, and this is to ensure consistency and accuracy.

Measurements are usually made using a microscope for accuracy, and sometimes the measurements can even be automated.

For each test, the load is removed slowly to ensure the indentation remains the same so it's not altered at all by releasing it quickly.

So we're now on to Task A.

First of all, I want you to explain how industrial hardness tests ensure consistency, accuracy, and reliability.

I then want you to use note and sketches and explain either the Vickers or the Brinell hardness test.

Pause the video now, have a go at this task, and come back to me when you've completed it.

So how did you get on? Well, let's have a look at some sample answers.

First of all, I wanted you to explain how industrial hardness tests ensure consistency, accuracy, and reliability.

Well, each test piece surface is cleaned and prepared so they are free from dirt and grease.

The load is slowly applied.

A specific load is applied for a specific time.

The indenter is a standardized shape.

Measurements are made using a microscope.

All of those reasons make sure that we have a consistent, accurate, and reliable result.

I then wanted you to use notes and sketches to explain either the Vickers or the Brinell hardness test.

And in this case, we've got the Brinell hardness test.

So I've got some nice sketches on there.

The test piece surface is prepared.

That's the first bit.

We've gotta make sure we've got the hardened steel ball indenter is pressed into the material's surface, and we're making sure we're saying it's for a specific load for a specific time.

The load is slowly removed, and the material is indented.

And then of course, we measure the diameter of the indentation to calculate the Brinell hardness number.

Well done.

So we're now gonna look at how we can replicate, to a certain degree, a hardness test in a school workshop environment.

Now we can, of course, do hardness tests in a school workshop.

They're not gonna be as accurate as doing one in industry, but it will still give us an understanding of how hard certain materials are and also gives a good comparison between materials.

We can use a hammer and a center punch.

An indent can be made and then measured on different materials.

For the tests, we're gonna focus on metals in this case.

And it's just really important that you wear safety glasses during these tests.

Now, to ensure consistency and accuracy, we're gonna lift the hammer the same distance from the material each time, and we can do that by placing a steel rule up against our test area.

And then all we need to do is just make sure we're lifting it to the right height.

And then what we're gonna do is let the weight of the hammer and the height from which it is dropped to provide the load.

Obviously, keep hold of the hammer, don't let go of the hammer, but hold the hammer and just allow it to drop.

And that will apply consistent tests.

The tools and equipment we need for this, it's really simple: we need a ball pein hammer and also a center punch, plus, obviously, our test pieces.

Let's have a look at the process.

So first of all, we're gonna cut the test materials to the same size or as close to the same size as we can, and it's useful if they are also the same thickness.

Prepare the surface of the materials to remove any dirt or grease, just like they do in industry.

Place the test piece on a hard surface and support a steel rule vertically so you can see how high you're raising that hammer.

Place the center punch onto the material, making sure you've obviously got your safety glasses on.

And then raise the hammer to the specific distance and drop to hit the punch.

Make sure you're only hitting it once.

Don't hit it multiple times.

And then what we're gonna do is measure the diameter of the indent.

Quick check for understanding.

Why is it important to apply the same load when testing material hardness? Is it A, so the results are consistent and can be compared accurately, B, so the test only measures the hardness of the material and not differences in load applied, or C, so the material automatically becomes harder under more load? Pause the video now, have a go at this, and come back to me when you've got your answer.

The answer is, of course, the first two, so the results are consistent and can be compared accurately, and also so the test only measures the hardness of the material and not the differences in load that we apply to them.

Well done.

Now, a hardness test, as we know, can be conducted in a school workshop, but we can also do what is known as a scratch test.

And this can be used to assess how well a material resists surface damage from scratching, which is also part of hardness.

Tools and equipment for this: we just need a scribe.

So let's have a look at the process of a scratch test.

Again, we're gonna cut the test materials to the same size.

In fact, you can use the same test pieces that you use for the indentation test.

Prepare the surfaces to remove any dirt or grease.

Secure your material to the workbench.

You can either use a clamp or you can actually secure it in a vice.

Run the scribe across the material, applying the same load each time.

And then examine your scratch closely under good lighting or possibly use a magnifying glass to see the scratch more clearly.

You can then make a judgment as to how easy it was to scratch the surface of the material.

So we're now on to Task B, and this is where you're gonna conduct your own workshop hardness testing.

I would like you to set up both an indentation test and a scratch test in your school workshop.

Test three metals, and then record your results.

Present your finding results in a table, and include comments as to which material is the hardest.

And you might wanna lay your table out a little bit like this.

So my headings, I have material, indent diameter, which I'm gonna measure in millimeters, the ability to resist scratching, and I've just done a scale from poor to very good.

I've got some comments and observations in there.

And then I've just given it my own hardness rating, with 3 being hard and 1 being not so hard.

Now, the first test piece I've got on here as an example is steel, and this was just low-carbon steel.

The indent diameter was only one millimeters.

It was very good at resisting scratching.

And you can see in my comment, it was very difficult to mark the steel with the scribe, so I'm gonna give it hardness rating of 3.

What I want you to do now is pause the video, carry out all these tests, fill in your table, and come back to me when you've completed your task.

So how did you get on? Well, hopefully your results look something similar to me.

You might have used different materials.

But as you can see from this, I have three materials with three different hardness ratings, with steel, as we've already talked about, being the hardest.

But I then had aluminum, and you can see the indent diameter was larger, being three millimeters.

It was actually quite good at resisting scratching.

I could scratch it.

It was easier than the steel, but not as easy as the copper, which of course had a larger indent.

And the copper was the least hardest material.

It was easily scratched, and obviously indent was the largest as well.

So I've given them a hardness rating of steel had a 3, aluminum had 2, and copper had a 1.

Now, what that's allowed me to do is compare these materials against each other in terms of hardness, and it's also given you some real-world experience so you can actually talk about material hardness using these experiences.

Well done with that task.

So that brings us to the end of this lesson.

Let's have a quick summary.

Hardness is a material's ability to resist scratching and indentation.

Vickers and Brinell are industrial hardness tests.

The Vickers and Brinell tests measure hardness by pressing an indenter into the material and observing the mark left.

A hardness test can be simulated in a workshop using a center punch and a hammer.

Hardness can be tested by scratching the surface of a material with a scribe.

Well done today.

You've been absolutely fantastic.

I look forward to seeing you all next time.

Goodbye.