Okay, sorry, in der letzten Lektion dieses Semesters.

Für diesen Kurs zumindest.

Last time we talked about fatigue testing.

But we also talked about fracture size effects.

I want to recap those fracture size effects again.

Does anyone remember which fracture size effects we talked about?

We have three different types.

We talk about ligament and thickness.

Those are two different size effects.

We start with the ligament size effects.

Size effects.

We have to remember what is the ligament in a fracture sample.

The ligament is the sample dimension in crack growth direction.

We have our notch and the crack growth direction is downwards.

The ligament length is this dimension here.

The whole sample dimension is called the sample width.

The crack length is called a.

The length is w minus a.

We talked about four different cases.

The first one was an ideally brittle material.

It shows no plastic deformation at all.

Then we talked about small scale yielding.

It shows a little amount of plastic deformation.

Then we had large scale yielding.

We talked about high amount of plastic deformation and general yielding.

The linear elastic fracture mechanics concepts were designed for ideally brittle materials.

They can also be applied to small scale yielding.

However, not to large scale yielding or general yielding.

The linear elastic fracture mechanics only takes into consideration linear elastic processes.

No plastic deformation.

However, if the plastic deformation is very small compared to the sample dimensions, you can still apply them.

Now for large scale yielding, so examples with more amount of plastic deformation, we need to use elastic plastic fracture mechanics.

Elastic plastic fracture mechanics can also be applied to these two cases.

It will show the same results.

It's just usually more work to do.

But there's no problem with applying the PFM here.

For general yielding, also elastic plastic fracture mechanics.

So now you might say, well, this isn't really a size effect.

This is just an effect of the material properties.

Because the plastic zone size increases from left to right.

The more ductile our material gets, the more we keep them the same size.

The more we go to the right of this joint.

However, if we keep the material properties the same and we reduce the size, then we will also go from that to right.

You can easily imagine this if you just take this sample with a very small plastic zone.

And now you just fabricate an even smaller sample out of that one.

That's only so large.

Then you automatically end up with large scale yielding conditions.

So it's very important that we know or that we can estimate the plastic zone size in relation to our sample dimensions.

If it gets very loud, we need to use PFM methods.

And if it gets too loud, we need to use the plastic zone size.