car brake pedal design excercise
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Autodesk Inventor®
Tutorial Exercise
SAE Car Brake Pedal Exercise. Autodesk Inventor
® Finite Element Analysis
Optimization
OBJECTIVE: To create simulations of various pedal designs that focus on
reducing the mass of the current design. The exercise involves
adding machined pockets on both sides of the pedals and
validating the design change in the Stress Analysis environment.
SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization
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Contents TOPIC .......................................................................................................................................................... 3
OPTIMIZING THE MASS OF A BRAKE PEDAL .............................................................................. 3
OBJECTIVE ........................................................................................................................................ 3
DESCRIPTION ................................................................................................................................... 3
DATASET ............................................................................................................................................ 4
DESIGN CRITERIA ............................................................................................................................... 4
KEY TERMS ........................................................................................................................................... 4
EXERCISE .................................................................................................................................................. 6
DESIGN CRITERIA ............................................................................................................................... 6
Create a New Simulation ...................................................................................................................... 6
Review the Materials ............................................................................................................................. 7
Add Constraints ...................................................................................................................................... 7
Add Loads ............................................................................................................................................... 8
Run a Simulation .................................................................................................................................... 9
CONCLUSION: ..................................................................................................................................... 10
Create an Extrusion ............................................................................................................................. 10
Run the Second Simulation ................................................................................................................ 11
CONCLUSION: ..................................................................................................................................... 12
Create a Second Extrusion ................................................................................................................. 12
Run the Third Simulation ..................................................................................................................... 12
CONCLUSION: ..................................................................................................................................... 13
SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization
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TOPIC
OPTIMIZING THE MASS OF A BRAKE PEDAL
OBJECTIVE
To create simulations of various pedal designs that focus on reducing the mass of the current
design. The exercise involves adding machined pockets on both sides of the pedals and
validating the design change in the Stress Analysis environment.
DESCRIPTION
The current design of the pedals is overbuilt and the new designs are focused on maintaining
the design specifications of the current design, while reducing the mass of the part.
Using Autodesk Inventor, Stress Analysis will be used to determine the stress, displacement
and safety factor of the design. The work flow will be repeated until the mass of the pedal
design is optimized against the design criteria. The initial mass of the brake pedal is 0.311 kg.
The optimized mass is 1.51 kg, a reduction of 51%. The design changes include:
1. Add a machined pocket to each side of the brake pedal.
2. Add a machined cut-out.
SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization
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DATASET
brakes_pedal_tray.iam
The part to be analyzed is brakes_brake_pedal.ipt.
DESIGN CRITERIA
YIELD STRENGTH (MPa) DEFLECTION (mm) SAFETY FACTOR
276 (AL 6061) 1.25 2.0
KEY TERMS
KEY TERM DESCRIPTION
assembly Two or more components (parts or subassemblies) considered as a single model. An assembly typically includes multiple components positioned absolutely and relatively (as required) with constraints that define both size and position. Assembly components may include features defined in place in the assembly. Mass and material properties may be inherited from individual part files. The brake pedal is the part being analyzed. It is a part within the brake tray assembly.
Stress analysis An analysis showing that the model is statically and dynamically stable and free from divergence on application of external loads and frequencies.
In this optimization, we are using stress analysis to ensure that the material and geometry of the pedal can handle the loads without deforming and failing.
SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization
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Simulation In the context of Autodesk Inventor, the term Simulation has grown to be an equivalent term to analysis. The analysis of the brake pedal uses Stress Analysis to optimize the mass of the pedal. Stress Analysis is used to analyze the material at the point of maximum load on the pedal.
von Mises Stress Three-dimensional stresses and strains build up in many directions. A common way to express these multidirectional stresses is to summarize them into an Equivalent stress, also known as the von-Mises stress. A three-dimensional solid has six stress components. Sometimes a uniaxial stress test finds material properties experimentally. In that case, the combination of the six stress components to a single equivalent stress relates the real stress system.
displacement Displacement is the amount of stretching that an object undergoes due to the loading. For this simulation a maximum deflection of 1.25 mm is allowed.
safety factor All objects have a stress limit depending on the material used, which are presented as material yield or ultimate strengths. If aluminum has a yield limit of 276 MPa, any stresses above this limit result in some form of permanent deformation. If a design is not supposed to deform permanently by going beyond yield (most cases), then the maximum allowable stress in this case is 276 Ma. The safety factor is how much stronger the system is than it needs to be for a given load. You can calculate a factor of safety as the ratio of the maximum allowable stress (Yield Strength) to the equivalent stress (von-Mises) under the maximum load.. In the final design iteration of the end cap, the Yield Strength of the material is 276 MPa and the von Mises value is 70.34 MPa. This gives a minimum safety factor of 3.91.
SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization
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EXERCISE In this exercise, you review a design for the
brake pedal in the Formula SAE race car
built by the Oklahoma University Sooner
Racing Team. The objective is to reduce the
mass of the pedal which is currently 0.311
kg.
Note that your results may vary slightly than
the figures quoted here.
DESIGN CRITERIA
The following table lists the maximum
allowable stress and displacement values
and the minimum allowable safety factor for
this exercise.
STRESS DISPLACEMENT SAFETY FACTOR
276 MPa 1.25 mm 2.0
The completed exercise
Create a New Simulation
In this section of the exercise, you open the
current version of the pedal assembly.
1. Make Brake Pedal.ipj the active project.
2. Open Brake Pedal Tray.iam.
3. In the graphics window, right-click the
red brake pedal assembly. Click Open.
4. In the browser, expand Representations
> Level of Detail: Master. This
representation was created to suppress
the parts that are not required for the
simulation.
5. Double-click StressAnalysis.
6. On the Environments tab, Begin panel,
click Stress Analysis.
SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization
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7. On the Manage panel, click Create
Simulation.
8. For Name, enter Pedal Simulation 1.
Ensure the default values of Single
Point Design Objective and Static
Analysis are selected.
9. Click OK.
10. On the Contacts panel, click Automatic.
Since there are no moving parts to be
considered in this assembly, you can
generate contacts automatically.
11. In the browser, expand the Contacts >
Bonded folder and review the contacts.
12. Collapse the Contacts > Bonded folder.
Review the Materials
In this section of the exercise, you review
the currently assigned materials.
1. On the Material panel, click Assign.
2. Review the Assign Materials dialog box.
For this simulation the Aluminum 6061
is correct.
3. Under the Safety Factor column, ensure
that Yield Strength is selected for all
parts.
Note: The Safety Factor is calculated on the Yield Strength or Ultimate Tensile Strength of the material. For example, if the Yield Strength of the material is 276 MPa and the von-Mises equivalent stress is 138 MPa the safety factor is 2.0 (276/138 = 2.0).
4. Click Cancel to close the Assign
Materials dialog box.
Add Constraints
In this section of the exercise, you add a pin
constraint and a frictionless constraint to the
pedal.
1. On the Constraints panel, click Pin.
2. Select the face of the hole as shown.
3. Click OK.
4. On the Constraints panel, click
Frictionless.
SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization
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5. Select the bottom face of the pedal as
shown.
6. Click OK. This constraint is required on
the bottom face of the pedal to meet the
requirements of the simulation and
ensure the design is not
underconstrained.
Add Loads
In this section of the exercise, you add
loads to the pedal.
1. On the Loads panel, click Force.
2. Select the face of the pedal as shown.
3. In the Force dialog box, for Magnitude,
enter 450 N.
Note: This value is typical of the force
applied to a brake pedal in an emergency
braking operation.
4. Click OK. The force load is added and is
displayed as a glyph on the face of the
part.
5. On the ViewCube, click the top-left
corner.
6. Zoom into the area on the pedal as
shown.
7. On the Loads panel, click Force.
8. Select the face as shown.
9. In the Force dialog box, for Magnitude,
enter 45.
Note: This force is applied to represent the
resistance force from the brake cylinders as
you apply force to the brake pedal.
10. Click Apply.
11. Rotate the assembly and select the
same face on the other side of the part,
as shown.
SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization
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12. Click OK.
13. On the ViewCube, click Home.
Run a Simulation
In this section of the exercise, you run a
simulation.
1. On the Solve panel, click Simulate.
2. Click Run.
3. In the browser, review the Results
folder. By default, Von Mises Stress is
active.
4. Review the Maximum and Minimum
values (your results may vary
slightly).The values are 73.81 MPa and
0.04 MPa respectively. Comparing
these values to the supplied design
criteria shows that the design is
compliant.
5. In the browser, double-click
Displacement.
6. Review the Maximum and Minimum
values. The values are 0.4493 mm and
0 mm respectively. Comparing these
values to the supplied design criteria
shows that the design is compliant.
7. In the browser, double-click Safety
Factor.
8. Review the Minimum value. The value is
3.73. Comparing this value to the
supplied design criteria shows that the
design is compliant.
9. On the Exit menu, click Finish Stress
Analysis.
10. In the browser, right-click
brakes_brake_pedal:1. Click Open. This
opens the part without the trunion
cages.
11. Right click on the part and select
iProperties.
12. On the Physical tab, click Update.
The mass of the brake pedal is 0.311
kg.
13. Click Close.
SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization
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14. Close the brakes_brake_pedal.ipt file.
15. On the Environments tab, Begin panel,
click Stress Analysis.
16. In the browser, double-click Von Mises
Stress.
17. On the Result panel, click Animate.
18. On the Animate Results dialog box, click
Play.
19. Repeat the animation for Displacement
and Safety Factor.
20. Close the Animate Results dialog box.
CONCLUSION:
The design results indicate that
modifications can be made to reduce the
mass of the pedal. The first modification is
to create 2 machined pockets on the upper
part of the pedal.
Create an Extrusion
In this section of the exercise, you extrude a
sketch to create a pocket on one side of the
pedal.
1. In the browser, if required, expand
brakes_brake_pedal_assm.iam
(StressAnalysis).
2. Right-click brakes_brake_pedal:1. Click
Open.
3. In the browser, right-click Sketch3. Click
Visibility.
4. On the Model tab, Create panel, click
Extrude.
5. Select inside the sketch profile as
shown.
6. Drag the distance arrow to the right to
create a cut and until 12 is displayed as
the depth.
7. Click the check mark.
8. On the Pattern panel, click Mirror.
9. In the graphics window, select the
extruded feature you just created.
10. In the Mirror dialog box, click Mirror
Plane.
SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization
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11. In the browser, select the Work Plane
entry.
12. Click OK.
13. Rotate the part to review the mirrored
feature.
14. On the ViewCube, click Home.
15. Save the part and close the file.
Run the Second Simulation
In this section of the exercise, you run the
second simulation by carrying over the
constraints, loads, and contacts that you’ve
already defined.
1. On the Quick Access Toolbar, click
Local Update.
2. On the Solve panel, click Simulate.
3. Click Run.
4. Review the Maximum and Minimum
values. The values are 73.02 MPa and
0.06 MPa respectively. Comparing
these values to the supplied design
criteria shows that the design is
compliant.
5. In the browser, double-click
Displacement.
6. Review the Maximum and Minimum
values. The values are 0.6154 mm and
0 mm respectively. Comparing these
values to the supplied design criteria
shows that the design is compliant.
7. In the browser, double-click Safety
Factor.
8. Review the Minimum value. The value is
3.77. Comparing this value to the
supplied design criteria shows that the
design is compliant.
9. On the Exit menu, click Finish Stress
Analysis.
10. In the browser, right-click
brakes_brake_pedal:1. Click iProperties.
(without opening the part).
11. On the Physical tab, click Update.
The mass of the brake pedal is 0.165
kg. This is a 47% reduction from the
mass of the initial design.
12. Click Close.
SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization
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13. On the Environments tab, Begin panel,
click Stress Analysis.
Note: You’ll notice that the value of the
maximum stress is lower than the first
simulation. Stress is now more evenly
distributed on the pedal. To view the area of
maximum stress, you can probe for the
maximum value.
CONCLUSION:
The design results indicate that further
modifications can be made to optimize the
design. The next modification is to create a
machined opening around the lower pivot.
Create a Second Extrusion
In this section of the exercise, you extrude
an existing sketch to create an opening
around the pivot.
1. In the browser, if required, expand
brakes_brake_pedal_assm.iam
(StressAnalysis).
2. Right-click brakes_brake_pedal:1. Click
Open.
3. In the browser, right-click Sketch6. Click
Visibility.
4. On the Model tab, Create panel, click
Extrude.
5. Select inside the sketch profile as
shown.
6. Select Cut from the list.
7. Select Through All from the list.
8. Click the check mark.
9. Save the part and close the file.
Run the Third Simulation
In this section of the exercise, you run the
third simulation by carrying over the
constraints, loads, and contacts that you’ve
already defined.
SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization
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1. On the Solve panel, click Simulate.
2. Click Run.
3. Review the Maximum and Minimum
values. The values are 70.34 MPa and
0.06 MPa respectively. Comparing
these values to the supplied design
criteria shows that the design is
compliant.
4. In the browser, double-click
Displacement.
5. Review the Maximum and Minimum
values. The values are 0.7225 mm and
0 mm respectively. Comparing these
values to the supplied design criteria
shows that the design is compliant.
6. In the browser, double-click Safety
Factor.
7. Review the Minimum value. The value is
3.91. Comparing this value to the
supplied design criteria shows that the
design is compliant.
8. On the Exit menu, click Finish Stress
Analysis.
9. In the browser, right-click
brakes_brake_pedal:1. Click iProperties.
10. On the Physical tab, click Update.
The mass of the brake pedal is 0.151
kg. This is a 51% reduction from the
mass of the initial design.
11. Click Close.
12. Save and close the file.
CONCLUSION:
The objective was to reduce the mass of the
pedal and that has been achieved. The
current design is 51% lighter than the
original design. What more can be done to
reduce the mass? In this assembly the
overall dimensions are controlled by 2
design criteria.
a. The length of the pedal which is
required for leverage.
b. The base of the pedal houses a
number of bearings that permit
easy rotation of the pedal in
operation. However, the overall
dimensions restrict any further
reduction of the pedal in that
area.
The stress, displacement, and safety factors
are all well within the design criteria, but the
design criteria prevent and more meaningful
reductions in the mass of the pedal. It is
now just 0.151 kg and further modifications
would not represent a significant reduction
for the cost and effort required.
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