Moonbuggy Rear Suspension Analysis

1

• Moonbuggy Rear Suspension Analysis
• ME450 Computer-Aided Engineering Analysis
• Department of Mechanical Engineering, IUPUI
• Instructor Dr. Koshrow Nematollahi
• May 1, 2006
• John Fearncombe
• Brandin Ray
• Amber Russell

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Objectives

• Perform finite element analysis of moon buggy
  suspension using ANSYS Workbench
• Evaluate stress and deformation resulting from
  applied load
• Perform iterations as needed until a satisfactory
  design is realized

3
Introduction

• Moon buggy originally designed in Spring 2005 by
  ME 462 design team
• Lower a-arms on original suspension failed
• Normal loading conditions were determined to be
  approximately 200 pounds-force
• The initial design was modeled to determine if it
  could be modified and safely used

4
Theoretical Background

• Utilized ten-node SOLID92 tetrahedral elements
• Ideal for complicated solids with curved
  boundaries

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Model Details for Existing Design

• Originally modeled in Pro/Engineer (IGES), then
  imported into ANSYS Workbench
• Static analysis only
• Aluminum alloy construction
• 200 pounds-force load applied at shock mount
• Fixed supports at axes of rotation
• Displacement constrained in transverse direction

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ANSYS Workbench Model of Existing Design
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Deformed Geometry for Existing Design

• Maximum Deflection of 2.7810-3 inches
• Maximum deformation occurs near shock absorber
  mount

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Principal Stresses for Existing Design

• Maximum principal stress of 1.791 ksi
• Yield stress for 6061 aluminum alloy is 35 ksi
• Maximum stresses occur where the part failed

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Shear Stress for Existing Design

• Maximum shear stress of 1.421 ksi
• Deemed insignificant
• Failure due to fatigue in aluminum

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Model Details for First Iteration

• Modeled and constrained as before
• Aluminum alloy construction
• 200 pound-force load again applied at shock mount
• Modeled as one-piece construction with no welds

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Results - ANSYS Model of First Iteration
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Deformed Geometry for First Iteration

• Maximum Deflection of 5.4210-3 inches
• Occurs below shock absorber mounting bolt

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Principal Stresses for First Iteration

• Maximum principal stress of 221.267 psi
• Yield stress for 6061 aluminum alloy is 35 ksi
• Maximum stresses occur near the shock absorber
  mounting bolt

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Shear Stress for First Iteration

• Maximum shear stress of 20.917 psi
• Shear stress concentrated near welds
• Quality of welds had been an issue

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Model Details for Final Iteration

• Modeled and constrained as before
• Aluminum alloy construction with steel
  reinforcement plates at shock absorber mount
• Two points of attachment to wheel hub housing to
  relieve stress on aluminum members

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ANSYS Workbench Model of Final Iteration
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Deformed Geometry for Final Iteration

• Maximum Deflection of .11410-3 inches
• Located at mid-section of shock absorber bolt

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Principal Stresses for Final Iteration

• Maximum principal stress of 1.875 ksi
• Yield stress
• 6061 aluminum alloy is 35 ksi
• 4140 steel is 45 ksi
• Maximum stresses occur in the steel reinforcing
  plates

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Shear Stress for Final Iteration

• Maximum shear stress of 1.170 ksi
• Located in steel reinforcing plates
• Achieved objective of localizing stresses within
  steel elements

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Impact Statement

• Through the use of finite element analysis on the
  rear suspension of the moon buggy the vehicle has
  become more safe, stable, and easier to maintain.
  
• By optimizing the design before production, we
  have alleviated costly and potentially dangerous
  failures.

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Conclusion - Advantages of Final Iteration

• Maximum stress is distributed on steel
  reinforcing plates
• Ability to quickly and inexpensively replace the
  parts most likely to fail
• Easier fabrication
• No reliance on welds for structural stability

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Suspension Test
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Bibliography

• ME 450 Course Text
• ANSYS Website www.ansys.com
• Car Suspension and Handling. Bastow, Donald.
  London Pentech Press Warrendale, Penn.
  Society of Automotive Engineers, 1993.
• Chassis design principles and analysis
  Milliken, William F., 1911-
• www.engineersedge.com Material Properties