Hello everyone.
Welcome to the next session of Answers Workbench Tutorials.
In this session we are solving for fatigue analysis of a plate with a circular hole in it.
So we will first go to static structure and double click on it.
Next, we'll go to geometry and new design modular geometry.
Units to the mm x y plane.
Look at Alphas.
Go to sketching and sketch a rectangle.
I'll give it some dimensions, say at 100 and edge to softie.
I'll extrude it.
I'll give the depth to say, 10 a.m. generate.
I want to draw a circular hole in it so I'll select the space on which I want.
Draw the hole.
I'll go to new plain generate then look at next I'll go to sketching and choose circle as the options.
I'll draw a random circle.
See, I give the diameter as 15.
And then I'm going to position it.
And there will be 50.
I want to place it at the center so this is 1525 Nextel extrude the schedule selected apply.
Operation will be cut material.
The depth is already chosen as the elements generate.
So this is a hole created in the plate.
This is my simple geometry.
Next, I'll go to engineering data.
Now, since we are talking about fatigue analysis, we need to talk about the alternating stress.
Mean stress over here.
Let me choose the scale as a type so that I can see the graph.
Yo, yo.
You can see the values of alternating stress.
If I see in Megaparsec, this is the value of stress generated.
Now I have already made a video on this topic wherein I have discussed about a circular plate with a
hole in it and all the explanation has been given in it.
You can go to the video.
So that explains this value of 86.2 being the stress for the material.
So if you see this graph, this alternating stress over here is one value and it is plotted over the
number of cycles of loading that can be subjected on the body.
Suppose if you have a loading of alternating type from zero to 100 to 0 and back to negative value of
100 and then again to zero.
This is called an alternating type of load, so the body can be subjected to any number of cycles and
it can be safe if the stress generated in the body is less than the stress that is 86.2.
But suppose if you are subjecting the body to a load such that the stress value on that body is more
than 86.2, then after the particular number of cycles, your body is going to fail.
So that's the basic concept of fatigue.
That is when you are subjecting the body again and again, the same type of loading and you see your
body is going to fail because you are loading and unloading in a cycle.
So let's see.
This is my model that I'm trying to open up.
Now I'll go to geometry and I'll see the solid, the material assigned, the structural steel, which
is the default material.
That is what we were discussing about.
Now we will go to mesh sizing.
Relevant center will choose fine update.
This is my simple message that I have done.
I have chosen fine mesh.
But this circle over here, which is a hole in a plate.
It is a point.
Well, in if you have a small crack being generated, then that is the point of initiation, of crack
propagation.
That is, from that point, the crack will propagate over your entire body.
Generally, it happens in the zone.
The reason being when you are manufacturing a hole, you are actually going through a cutting operation.
When you do a cutting operation and you are cutting out the material.
There could be certain ends which has got cracked because of the tool interaction with the body.
There is a rough cutting done, so when you do a cut on the body, obviously it is possible that a small
nick or a small cut can be left on the body from where you crack and propagate over the entire body.
So because of which cutting operation is very sensitive operation, and when you have a hole in the
blade, this is the point where your stress concentration is there.
It is called as not sensitivity area, which means you can have a notch over there wherein you are if
a crack is generated, it will propagate on the entire body.
That's the basic meaning of notch sensitivity.
So now let's apply some load and check what happens to the body.
First, I'll go to analysis settings.
On the side I want to apply fixed and on the other end I will apply force.
Now, this force is something that we will discuss about as we go through the analysis.
Let's initially start with applying a small amount of force.
You can see this is X direction.
So I'll apply a force of, say, ten Kilo Newton.
Then I'll go to solution.
I want to see the total deformation on this body because of the loading.
I also want to see the equivalent stress which is generated on the body so that I can know as to how
much stress this load creates and whether my body is going to be the safe zone.
Or maybe after some amount of loading or a particular duration of time when you continuously load and
unload the body, my body is going to fail.
So how many cycles it is going to endure the load for?
I want to insert a new tone, which is far less fatigue, because that is what we are doing.
We are doing the fatigue testing for this plate with a hole in it.
Now you can see here this is the entire concept of fatigue, which is shown in answers.
There are various types of stress correction theory.
One is called S, s and Co.
S is the alternating stress on the body.
And N is a number of cycles.
That is what you saw over here.
So this is your alternating stress which is generated on the body because of the load and cycles over
here.
So this is nothing but your ascend co.
Any stress on the body below this curve is always going to indicate that your body is in a safe zone.
But if at all your stress generated falls above this graph, it indicates that your body is in a zone
wherein, after a particular number of cycles of loading on it, it is going to fail.
So whenever your stress intersects this graph, that point will be showing your condition of the body.
So let's get back to this.
And we will also talk about other theories like good man theory, Soderberg theory and Gerber theory.
These are the various theories.
You can take up any one theory and solve by default.
Your is selected so we can go for any other type as well.
So you can see here this is your ascent which is showing you.
Let's go to this left hand side.
You can see here the type of loading is fully reversed.
Fully reversed means you are going from a particular value to zero to its same negative value.
Then again, back to zero to the positive value to zero back to the negative value.
And this continues.
So when you apply a loading of this sort, this is called as fully reversed loading.
There are other types also, for example, zero base, zero based means you start from a particular
value, you go to zero again, you go to the value to zero and again to the value.
This is only one ended load.
That is, it is only towards the positive side, whereas fully reversed means you have the loading in
the positive as well as in the negative side.
Now there are two more over here.
One is for this ratio you can see here, ratio means your loading will be in a particular ratio like
from 1 to 1 is a ratio or it can have more.
Now this ratio can also be changed.
For example, scale factor is one.
If you want, you can change the scale factor to two.
So you can see the value has increased to two maximum loading and you can change it.
That's your choice.
So this is for this ratio and another type is history data.
When you have history data, it means you have some amount of value which is stored and you can use
that data.
So we are not going into that type.
We are going mainly into fully divorced and zero based because these are the type of loading which you
generally see.
And don't forget to change your scale factor to one.
Now, apart from this, you can see here in options analysis type, the analysis type is of stress life.
You are checking as to how much stress is generated and what would be the life of the body.
When we have mean stress theory, you can change it.
You can see here there are four types, as you can see here will go to good theory and the stress component
will be off if you are in one mises type.
So this is what we have chosen in certain tool.
If you right click you can insert the life term, which means you can see what would be the life of
this body.
Also, you can insert the CFD factor wherein you can see the factor of safety which is generated in
this body.
They mean something.
Obviously, we will discuss that and we will also talk about damage.
So these are the three things that we are going to discuss in this analysis.
Now I'll go to solution and so on.
We go to total deformation.
This is a total deformation over the body.
You can go to animation and you can check its animated view.
Next, we are going to equal in stress.
You can see here the stress generated a 68.084, which is less than 86 megaparsec.
You can take the unit over here this megaparsec.
So it is less than 86 megaparsec which means my body is.
Let's talk about the lights.
Now you can see here this is the number of cycles that can be loaded on this body.
And your body is going to be safe if your body is subjected to a stress which is lower than the maximum
stress, for example, in structural steel, that is 86 megaparsec.
If it is less than that, your body can endure a number of cycles and the body will be safe.
If you go more than 86, your body will see obviously after performing some amount of cycles, not fail
means immediate failure.
Let's talk about safety factor.
Safety factor over your is shown here as the design lines and this is your result 1.2661 thus value.
Please note if it is more than one, it means your body safe.
Suppose this value falls below 10.20.50.30.9.
You can say that your body is going to fit, but when it is more than one, it means your body is six.
You do not worry about it.
Now, let's talk about the damage factor.
You can see over here that since your number of design life is this and also the life is going to be
this value, then you divide both of them, this higher value divided by the life value.
You will get this damage factor.
This is thousand, which means it is quite high and your body is going to be a zone wherein you are
going to have failure.
The storm fatigue damage is nothing but the ratio of design life to the available life.
So this is your design life and this is the available life or you, as you can see now, we can discuss
about it by changing the value.
Currently my body is safe so I need not worry.
Let's talk about a higher loading suppose of the body subjected to.
For example, this was ten kilometers.
Then let me make this to 100 kilometers and then run the solution again for the same 30, for the same
type of loading that is fully reversed.
Now let's talk about total deformation.
This is the value of total deformation in 0.1118 equivalent stresses.
680 megaparsec.
It is much higher than the value that structural steel has given as a value that is 86 megaparsec,
which means my body will not be able to have that much amount of life like it would have had if the
load would have been included.
So let's go to the tool now and check look at the life.
Now, the life is only going to be 830 cycles more than this.
The body is not going to sustain.
Let's talk about the safety factor.
You can see here the ratio is 0.12, which means your value has fallen below one means your body is
not going to have a very good life.
Also, you can see here, the body was designed for one in 10 to 9 cycles, but life value shows as
to how many cycles it is going to sustain.
Let's talk about damage.
Damage stays.
It is the ratio of the design life to your life, which is going to be available for the body.
So you can see here this is the maximum ratio which you have found.
So that indicates that after a particular value, your body is going to fail.
This is the maximum number of cycles it can sustain.
And the life over your shows, the minimum number of cycles it can follow, 830 it will definitely sustain
and maximum value is that 1.26 or you, but it will fail somewhere between these two then it cannot
be exactly said, but it can be definitely failing between both of them.
Also, you can read here the tabulated data to the right inside minimum value 1000 maximum is these
this number.
So that is how the body is going to fail.
So we discussed this for a particular type that is fully reversed and good when type journey.
Let's talk about zero base load means it goes from zero to a particular value back to zero and again
to a particular value, we are using the same 30 GOODMAN So we will go to solution and solve.
Let's see.
Suppose if the type of loading is change on the body, keeping the load as 100 kelvin.
Now what happens to the body?
You can see the deformation is approximately the same equivalent stresses also the same.
Let's talk about the lights.
You can see here the life is reduced.
It has become 123 cycles, which means if you have this type of loading and that two in a zero based
type, which is not fully reversed, like you're starting from zero going to a higher value back to
zero to a higher value.
And this kind of cycle, if you follow your cycles, are going to be very less for which your body is
going to sustain, which means after 1.3 cycles, what you will give up, it will stop working and it
will fail.
Let's talk about the CFD factor.
You can see it is 0.21.
These are the same design life for which you are designing the body for working.
This is your damage factor.
You can see the ratio of here and you can see here this is the minimum value which is short.
So this is the number of cycles, minimum that it is going to sustain.
And this was the other value which you follow.
So this is how you analyze a body for fatigue analysis.
And by using software you can find out the life number of cycles it can sustain the damage that can
be caused on the body, whether your body is going to fail or not, for a particular material, for
a particular loading.
So that's how without making a prototype and going for destructive type of testing, you can use software
which is a non-destructive type of testing, and you can actually analyze what will be the threshold
value which the body is going to sustain.
Now, this is a common doubt as to how do we calculate the threshold value.
Now for that, obviously you will have to go for computation combination technique.
That is, you will have to keep on changing the value of this load from ten to the 100 kilometres that
I have taken.
Obviously the scale is too high, but you can go on taking some intervals and checking the values such
that a particular value will be reached, at which you can say that above this value my body will be
having a life which will be determined value which will be not like the desired value.
It will be less than that.
And below that value, whatever amount of load you applied, say 15 kilograms could be the limit.
That's an assumption that I make.
If it is so below 15, then whatever load you apply, your body is more than 15 kilometers.
This body is going to fail.
So that's how.
Values can be analyzed.
So with this, I end the session.
I hope you have understood the technique of fatigue analysis.
If you have any doubts, please write to me in the comment section.
See you in the next session.
Thank you.