Car Brake Pedal Design Excercise....... by Tuhin Srivastava

Autodesk Inventor速 Tutorial Exercise

SAE Car Brake Pedal Exercise.

Autodesk Inventor速 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速 Finite Element Analysis Optimization

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速 Finite Element Analysis Optimization

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速 Finite Element Analysis Optimization DATASET brakes_pedal_tray.iam

The part to be analyzed is brakes_brake_pedal.ipt.

DESIGN CRITERIA YIELD STRENGTH (MPa) 276 (AL 6061)

DEFLECTION (mm) 1.25

SAFETY FACTOR 2.0

KEY TERMS KEY TERM assembly

Stress analysis

DESCRIPTION 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. 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. 4

SAE Car Brake Pedal Exercise: Autodesk Inventor速 Finite Element Analysis Optimization Simulation

von Mises Stress

displacement

safety factor

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. 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 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. 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 (vonMises) 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速 Finite Element Analysis Optimization

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.

3. In the graphics window, right-click the red brake pedal assembly. Click Open.

DESIGN CRITERIA The following table lists the maximum allowable stress and displacement values and the minimum allowable safety factor for this exercise. STRESS

DISPLACEMENT

276 MPa

1.25 mm

SAFETY FACTOR 2.0 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. 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. 6. On the Environments tab, Begin panel, click Stress Analysis. 6

SAE Car Brake Pedal Exercise: Autodesk Inventor速 Finite Element Analysis Optimization 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. 3. Under the Safety Factor column, ensure that Yield Strength is selected for all parts.

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.

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. 12. Collapse the Contacts > Bonded folder.

Review the Materials In this section of the exercise, you review the currently assigned materials.

2. Select the face of the hole as shown.

1. On the Material panel, click Assign.

2. Review the Assign Materials dialog box. For this simulation the Aluminum 6061 is correct.

3. Click OK. 4. On the Constraints panel, click Frictionless.

SAE Car Brake Pedal Exercise: Autodesk Inventor速 Finite Element Analysis Optimization

5. Select the bottom face of the pedal as shown. 6. Zoom into the area on 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.

7. On the Loads panel, click Force.

8. Select the face as shown.

1. On the Loads panel, click Force.

2. Select the face of the pedal as shown.

9. In the Force dialog box, for Magnitude, enter 45.

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.

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.

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.

SAE Car Brake Pedal Exercise: Autodesk Inventor速 Finite Element Analysis Optimization

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. 9

SAE Car Brake Pedal Exercise: Autodesk Inventor速 Finite Element Analysis Optimization 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.

5. Select inside the sketch profile as shown.

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.

6. Drag the distance arrow to the right to create a cut and until 12 is displayed as the depth.

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).

7. Click the check mark.

8. On the Pattern panel, click Mirror. 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.

9. In the graphics window, select the extruded feature you just created. 10. In the Mirror dialog box, click Mirror Plane. 10

SAE Car Brake Pedal Exercise: Autodesk InventorÂŽ Finite Element Analysis Optimization 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 youâ&#x20AC;&#x2122;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 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.

6. Select Cut from the list.

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

7. Select Through All from the list.

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. 8. Click the check mark.

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.

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. 12

SAE Car Brake Pedal Exercise: Autodesk InventorÂŽ Finite Element Analysis Optimization 1. On the Solve panel, click Simulate.

2. Click Run.

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. 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.

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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