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  • [train passing]

  • piano background music

  • (Alan) Non-destructive testing covers

  • a wide range of techniques

  • used in industry and science.

  • And the samples are evaluated

  • in terms of their material properties

  • without causing any damage

  • and is therefore often carried out

  • in the workplace.

  • (Steve) Non-destructive testing

  • is extremely important to industry

  • because it allows the component

  • to be used after it's been tested.

  • OK, what we've got here is

  • Dye Penetrant Testing,

  • a very, very simple test

  • and it's used to detect open pores or

  • cracks that break the surface.

  • This is quite important because

  • if these defects go undetected

  • it could lead to some catastrophic

  • failure and potentially deaths.

  • We've got the dye.

  • We've got cleaning fluid. OK.

  • And we've also got some developer

  • like a talcum powder substance.

  • It's a very, very simple

  • technique to do so

  • you'd be using it in aerospace,

  • you'd be using it in railways,

  • you'd be using it in heavy industry.

  • The uses are pretty much limitless.

  • So first we need to clean the sample

  • to get rid of any grease or dirt.

  • [spray hisses]

  • And then we're ready

  • to apply the penetrant.

  • [spray hisses]

  • And then you've got to give it

  • sufficient time for the penetrant

  • to seep in to any

  • surface breaking defects.

  • The finer the defect

  • you're trying to detect,

  • the longer you need to leave it.

  • OK, so this has been sat for about

  • 20-30 minutes, and it should be

  • sufficient time for

  • the penetrating media

  • to seep into any open voids.

  • OK. So the next stage of this

  • is we've got to wipe off

  • any excess penetrant.

  • Get a rag, some of the cleaner.

  • Spray the cleaner onto the rag

  • and then just wipe off any excess.

  • Nice and simple.

  • The next section is

  • to get the developer...

  • and we give the surface

  • a nice, liberal, even coating.

  • [spray hisses]

  • OK, so we've left this sample

  • 10 minutes to develop,

  • and what we can see is there's a crack

  • emanating down the middle

  • of this sample. You can see that,

  • all the red that's coming out.

  • You can also see it

  • round these holes and

  • round the edges that's just where

  • we didn't clean inside the holes

  • and inside the edges

  • so that penetrant is then being

  • sucked back into the developer.

  • What we've got here

  • is one that came in from testing.

  • This is a real life component.

  • This is the bottom of a glass mould,

  • and on the back of that we've done

  • a Dye Penetrant Test and you can see

  • about 4 nice fine cracks than run

  • all the way through that specimen.

  • OK, so that's Dye Penetrant Testing.

  • A very nice cheap and quick way

  • of detecting defects without damaging

  • the actual component or material.

  • OK, the next test we're going to do is

  • Magnetic Particle Inspection.

  • And for that, we need a fluid

  • containing some magnetic particles,

  • we need a background contraster,

  • and we need a cleaner.

  • We also need a magnet.

  • Now we've got an electromagnet here.

  • You can also use permanent magnets,

  • although the difficulty is taking them

  • off if you've got nice strong magnets.

  • So the advantage of this technique over

  • Dye Penetrant Testing is that you can

  • detect slightly sub-surface defects.

  • The main disadvantage is that you've

  • got to be able to magnetise the

  • materials so non-magnetic materials

  • you can't test using

  • Magnetic Particle Inspection testing.

  • So the first thing we need to do is

  • clean the sample.

  • [spray hisses]

  • And then the next stage is to spray on

  • your contrasting background.

  • And then give it a nice, even coating.

  • [spray hisses]

  • And then we need to leave it to dry

  • before we can apply the ink

  • and the electromagnet.

  • OK, the sample's now dry so we need to

  • bring the sample in contact with the

  • electromagnet.

  • I'll need to make sure

  • we get good contact there.

  • Turn on, to magnetise the sample

  • and we spray on the magnetic ink.

  • [spray hisses]

  • So what's happening here is

  • we're inducing a magnetic field

  • into the material,

  • if there's defects within the material

  • those can deviate the lines of

  • magnetic field

  • and that's where the magnetic ink

  • that we sprayed on will congregate.

  • And that's what we can see here.

  • If we'd have been testing

  • this component in industry,

  • because we've identified these cracks,

  • which are detrimental to the component,

  • we'd just probably throw it away.

  • If we didn't see any cracks,

  • if it was deemed as good,

  • then we'd have to make sure that

  • we cleaned it off so that any materials

  • on here that might want to contaminate

  • the component for further work

  • or its service life.

  • OK, just to recap then, the

  • Dye Penetrant Test allows us to detect

  • surface breaking defects.

  • The Magnetic Particle Inspection allows

  • us to detect slightly sub-surface

  • defects, and what we've got here is

  • Ultrasonics. And that allows us to look

  • right inside the material.

  • OK, so this is us sample,

  • this is us ultrasonic probe,

  • and this is where we can see the signal

  • coming back and detect any

  • potential differences in the material.

  • So this is exactly the same sort

  • of technique you'll see in hospital,

  • maybe looking at babies, maybe looking

  • at kidney stones, that sort of thing.

  • OK, first of all we need to put on

  • a couplant. And this is something that

  • excludes air from the sample

  • and the probe.

  • Sound doesn't travel very well

  • through air, so we need to exclude

  • as much of it as possible.

  • Once we've got the couplant on,

  • we pop us probe on top and then

  • give it a wiggle round to exclude

  • any air. OK. So the width of this

  • screen is the equivalent of

  • 100mm depth. Now at the end of this

  • screen you can see there's a spike

  • there, and that's the reflection

  • from the back wall of the sample.

  • As we traverse along this sample,

  • what we'll start to see...

  • is... a spike appearing at about

  • 45mm there. Which is a reflection

  • from this top surface here.

  • As we continue to traverse, we get a

  • reflection at about 15mm and what

  • that is is a defect 15mm down from

  • the surface.

  • Again, continuing the traverse,

  • because that's only a small defect

  • that disappears whereas we're still

  • detecting this defect that's 45mm down.

  • If we carry on traversing across,

  • eventually the one at 45mm disappears

  • and then we start getting the back wall

  • signal reappearing at 100mm.

  • What makes ultrasonic testing different

  • to some of the other non-destructive

  • testing techniques you've seen is that

  • it can detect defects, maybe

  • gas as little bubbles or tiny cracks

  • within the material but those could be

  • meters away from the surface

  • of the material. And that makes it

  • a very powerful technique.

  • (Alan) This is a Scanning Electron Microscope.

  • This is the most sophisticated bit of

  • equipment we have in the

  • Materials Research Institute.

  • The Scanning Electron Microscope

  • enables us to do two or three things

  • that we haven't been able to do with

  • optical microscopy. The first is we can

  • now look at material at very high

  • magnification.

  • An optical microscope will only go

  • up to about 1000 times magnification.

  • With the electron microscope, we could

  • be looking at 500,000-800,000 times

  • magnification.

  • It's no good just making things bigger

  • if you can't then resolve the detail.

  • The electron microscope gives us

  • extremely good resolution

  • at very high magnification.

  • It's actually made up of some

  • very small, simple ideas

  • which if you bring them all together

  • make it into an incredibly sophisticated

  • piece of equipment.

  • At the top of the column

  • there's a tungsten filament.

  • That filament is heated up

  • and that gives off electrons.

  • The electrons come down the column.

  • They're focused by the electromagnets

  • onto the surface of the sample

  • and there they do two things.

  • One is that they create the image that

  • we see on the screen and the other is

  • that they allow us to do some chemical

  • analysis of the sample if we need to.

  • Basically put, the electrons hit into

  • the surface of our sample fairly hard

  • and knock out electrons

  • from the surface which are

  • characteristic of the element which

  • the sample is made from.

  • With this bit of equipment, we can

  • really get to almost the atomic level

  • to say what's controlling

  • and influencing the material behaviour.

  • As a Materials Engineer I love this

  • piece of equipment because we can do

  • so many incredible things with it.

  • We can use it to develop new materials,

  • we can use it to enhance existing

  • materials and we can even use it to

  • solve crimes in Forensic Engineering.

  • Forensic Engineering uses the

  • fundamentals of maths, physics and

  • some inorganic chemistry to inform and

  • augment legal argument.

  • A classic forensic investigation that

  • we get involved in here is where

  • there's been a road traffic incident.

  • Two cars have collided. One claims that

  • it's the other car's fault because he

  • didn't have his lights on and therefore

  • they couldn't see it. The police bring

  • the broken lamps to us and ask us

  • if we can establish whether the lamp

  • was illuminated just prior

  • to the collision.

  • And we can do that,

  • using our electron microscope.

  • So the chamber's now evacuated.

  • We've turned the electron beam on.

  • Let's have a look and see what we can

  • see in the electron microscope.

  • What we can see here is the tungsten

  • filament removed from the vehicle

  • and the first thing we notice is that

  • there are these globules

  • on the surface.

  • When we do the chemical analysis

  • of those globules we identify them

  • as silica and that silica is from the

  • glass bulb which broke

  • during the collision and showered down

  • onto the filament.

  • The fact that they're globular tells us

  • that this filament must have been hot

  • when that glass landed on its surface.

  • The filament being hot tells us that

  • the filament was illuminated

  • and therefore the motorist who was

  • driving this car was not guilty of

  • driving without their lights on.

[train passing]

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材料研究室では、非破壊検査 - ネットワークレール工学教育(15件中15件 (In The Materials Lab, Non-Destructive Testing - Network Rail engineering education (15 of 15))

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    Wonderful に公開 2021 年 01 月 14 日
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