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Set up, perform, and review results for a thermal stress simulation.
Type:
Tutorial
Length:
7 min.
Transcript
00:03
This is an industrial brake rotor much larger than the rotors on your car or truck.
00:09
The simulation model is a 1/8 symmetry portion of the full rotor.
00:14
Here we see the result and stresses due to the applied mechanical and thermal loads.
00:20
Let's take a step back and see what's required to set up and run this study.
00:27
First, we need to create a new simulation study.
00:29
Choosing the thermal stress analysis type.
00:33
Let's go into the study settings and change
00:35
the default stress free temperature to 25 C.
00:40
We'll also specify an absolute mesh size of six millimeters which will
00:44
give us two elements through the thinnest sections of the model.
00:50
Of course, the production model includes the full rotor.
00:53
We'll next go into the simplify workspace to
00:56
reduce the model to a 1/8 symmetry variant
00:59
changes performed here have no effect on the production model.
01:02
They are specific to the simulation process.
01:06
Split the full model at each of the
01:08
three global planes which produces eight separate bodies
01:12
using symmetry gives us two advantages.
01:16
First,
01:16
the model size is reduced which consumes less
01:18
storage space and the solution time is decreased.
01:22
And second, the application of constraints is very straightforward.
01:26
We can fully constrain the model against motion in all three
01:29
global directions without impeding the natural thermal expansion that we expect.
01:34
Constraining thermal stress models can be tricky because over
01:37
constraint can result in severely exaggerated thermal stresses.
01:43
Next,
01:43
we determine which body is the one located at the nearest
01:46
side in the first or plus X plus Y quadrant.
01:50
Then we keep this body and remove the other seven.
01:57
We can now return to the simulation workspace.
02:03
Notice that the model material has already been specified as gray cast iron as
02:07
T ma 48 grade 50.
02:10
We'll keep this material for the thermal stress study
02:14
in simulation.
02:15
When loads constraints and geometry are symmetrical,
02:18
there is no motion in the direction normal to the plane of symmetry.
02:21
So we constrain the following
02:24
the X translations on the faces lying along the YZ plane,
02:29
the Y translations for faces along the XZ plane
02:36
and the Z translations for faces along the xy plane.
02:41
Note that none of these constraints impede the radial or
02:43
axial growth of the rotor as it heats up.
02:48
Let's apply a pressure load of 13.8 mega pascals at the hub bore
02:52
to represent the load from the shrink fit between the shaft and rotor.
02:56
This is the only mechanical load.
02:60
The rotor is mounted to a water
03:01
cooled shaft. So we'll apply a fixed temperature of 38 C to this same face
03:08
will define a heat input of 36,500 watts per
03:12
meter squared to the brake pad contact face.
03:16
This value represents the average heat input to the
03:18
rotor over time on a per unit area basis,
03:22
the heat is generated as a result of friction between the pad and rotor.
03:26
When the braking force is applied.
03:29
Lastly,
03:30
we'll apply a convection load to all the exposed faces of the rotor,
03:33
both interior and exterior except for the brake pad contact face.
03:38
This exclusion is conservative since we're
03:40
ignoring the convective cooling along the
03:42
portion of the face that's not covered by the brake pad,
03:46
do not apply thermal loads at the faces along the symmetry planes.
03:50
Also, the program won't let you apply convection to the hub boor.
03:53
Since we've already fixed the temperature of that face,
03:58
the convection coefficient is 190 watts per meter. Kelvin
04:02
and the ambient air temperature is 25 C.
04:05
This convection value is higher than you would specify
04:08
for stagnant air with only buoyancy driving the convection.
04:12
The value takes into account the spinning of the rotor and therefore
04:15
the higher speed of the air flowing over and through it.
04:19
The model is ready to solve
04:26
when the solution finishes. The safety factor results are displayed
04:30
notice the minimum safety factor is slightly
04:32
more than 2.0 for the assumed conditions.
04:39
Now, we can talk through the other available results examining the
04:43
von
04:43
mises stress
04:47
displacement
04:50
temperature
04:53
and heat flux
04:55
the area of greatest heat flux is where the slots are located.
04:58
These openings allow cooling air into the rotor interior.
05:02
Not surprisingly,
05:03
this is also where the steepest temperature gradients and maximum stresses occur.
Video transcript
00:03
This is an industrial brake rotor much larger than the rotors on your car or truck.
00:09
The simulation model is a 1/8 symmetry portion of the full rotor.
00:14
Here we see the result and stresses due to the applied mechanical and thermal loads.
00:20
Let's take a step back and see what's required to set up and run this study.
00:27
First, we need to create a new simulation study.
00:29
Choosing the thermal stress analysis type.
00:33
Let's go into the study settings and change
00:35
the default stress free temperature to 25 C.
00:40
We'll also specify an absolute mesh size of six millimeters which will
00:44
give us two elements through the thinnest sections of the model.
00:50
Of course, the production model includes the full rotor.
00:53
We'll next go into the simplify workspace to
00:56
reduce the model to a 1/8 symmetry variant
00:59
changes performed here have no effect on the production model.
01:02
They are specific to the simulation process.
01:06
Split the full model at each of the
01:08
three global planes which produces eight separate bodies
01:12
using symmetry gives us two advantages.
01:16
First,
01:16
the model size is reduced which consumes less
01:18
storage space and the solution time is decreased.
01:22
And second, the application of constraints is very straightforward.
01:26
We can fully constrain the model against motion in all three
01:29
global directions without impeding the natural thermal expansion that we expect.
01:34
Constraining thermal stress models can be tricky because over
01:37
constraint can result in severely exaggerated thermal stresses.
01:43
Next,
01:43
we determine which body is the one located at the nearest
01:46
side in the first or plus X plus Y quadrant.
01:50
Then we keep this body and remove the other seven.
01:57
We can now return to the simulation workspace.
02:03
Notice that the model material has already been specified as gray cast iron as
02:07
T ma 48 grade 50.
02:10
We'll keep this material for the thermal stress study
02:14
in simulation.
02:15
When loads constraints and geometry are symmetrical,
02:18
there is no motion in the direction normal to the plane of symmetry.
02:21
So we constrain the following
02:24
the X translations on the faces lying along the YZ plane,
02:29
the Y translations for faces along the XZ plane
02:36
and the Z translations for faces along the xy plane.
02:41
Note that none of these constraints impede the radial or
02:43
axial growth of the rotor as it heats up.
02:48
Let's apply a pressure load of 13.8 mega pascals at the hub bore
02:52
to represent the load from the shrink fit between the shaft and rotor.
02:56
This is the only mechanical load.
02:60
The rotor is mounted to a water
03:01
cooled shaft. So we'll apply a fixed temperature of 38 C to this same face
03:08
will define a heat input of 36,500 watts per
03:12
meter squared to the brake pad contact face.
03:16
This value represents the average heat input to the
03:18
rotor over time on a per unit area basis,
03:22
the heat is generated as a result of friction between the pad and rotor.
03:26
When the braking force is applied.
03:29
Lastly,
03:30
we'll apply a convection load to all the exposed faces of the rotor,
03:33
both interior and exterior except for the brake pad contact face.
03:38
This exclusion is conservative since we're
03:40
ignoring the convective cooling along the
03:42
portion of the face that's not covered by the brake pad,
03:46
do not apply thermal loads at the faces along the symmetry planes.
03:50
Also, the program won't let you apply convection to the hub boor.
03:53
Since we've already fixed the temperature of that face,
03:58
the convection coefficient is 190 watts per meter. Kelvin
04:02
and the ambient air temperature is 25 C.
04:05
This convection value is higher than you would specify
04:08
for stagnant air with only buoyancy driving the convection.
04:12
The value takes into account the spinning of the rotor and therefore
04:15
the higher speed of the air flowing over and through it.
04:19
The model is ready to solve
04:26
when the solution finishes. The safety factor results are displayed
04:30
notice the minimum safety factor is slightly
04:32
more than 2.0 for the assumed conditions.
04:39
Now, we can talk through the other available results examining the
04:43
von
04:43
mises stress
04:47
displacement
04:50
temperature
04:53
and heat flux
04:55
the area of greatest heat flux is where the slots are located.
04:58
These openings allow cooling air into the rotor interior.
05:02
Not surprisingly,
05:03
this is also where the steepest temperature gradients and maximum stresses occur.
Want to try this? In the Fusion Data Panel, open the start file from Samples > Basic Training > 11 - Simulation > BrakeRotor.
For more, see Thermal stress analysis.
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