ME 501 Final Project:ME 501 Final Project:Analysis of Ford Analysis of Ford
Expedition Expedition Frame CrossmemberFrame Crossmember
June 20, 2001June 20, 2001
John SmartJohn Smart
Andy StanselAndy Stansel Courtesy Ford Motor CompanyUsed without permission
Presentation Outline
• Project Background and Objective
• Modeling—meshing, boundary conditions.
• 3 loading conditions
• Results
• Conclusions
Project Objective
Modeling—ProE Model
• Both crossmembers were created in Pro/E
Frame rails
OEM Crossmember
New crossmember
New crossmenber dimensions
Modeling—Ansys Model
• Export Pro/E model as an IGES file
• Import the IGES file into ANSYS
• Set element type as “Shell 63” (3D, 4 node element, 6 DOF per node)
• Set shell thickness to .125”• Material properties of steel (E=30 Mpsi, =.27)
1040 Steel, Sy = 86 kpsi
Modeling—Meshing
• Several different meshes were tested
Coarse & fine free meshing
4 elements thick
Fine mapped meshing
2,544 elements2,546 nodes15,276 DOF (unconstrained)
#1 Fixed
#2 Chase boundary
Modeling—Boundary Conditions
• Two separate boundary conditions were tested
OEM crossmember
symmetry
Difference of 8 kpsi
Difference of 2 psi! Therefore, we used fixed-fixed conditions
Modeling—Boundary Conditions
• Two separate boundary conditions were testedNew crossmember
#1. Fixed, fixed
#2. Quasi-simply supported
Loading Condition #1
• Vehicle at rest, or driving straight, or landing from jump.
Fixed
Fixed
1,000 lbs.
1,000 lbs.
New crossmemberOEM crossmember
Fixed
Rollers
1,000 lbs
Loading #1— Results
OEM crossmember
Maximum deflection=.022”
New crossmember
Maximum deflection=.0335”
Y-displacement
Bulges out here
Loading #1— Results
New crossmember
Max eq. stress: 34 kpsi
Factor of safety: 2.5
Max eq. stress: 47 kpsi
Factor of safety: 1.8
OEM crossmember
Loading Condition #2
• Frame rails twist due to terrain. This induces torsion in the crossmember.
fixed
500 ft-lbs
OEM crossmember
fixed
500 ft-lbs
New crossmember
Loading #2—Results
OEM crossmember New crossmember
Max deflection: 0.0325”
Max deflection: 0.0308”
Loading #2—Results
New crossmember
Max eq. stress: 8.8 kpsi
Factor of Safety: 9.7
OEM crossmember
Max eq. stress: 7.6 kpsi
Factor of Safety: 11.3
Loading Condition #3
• Pure bending in crossmember
fixed
1,000 lbs
fixed
1,000 lbs
OEM crossmember New crossmember
Loading #3—Results
OEM crossmember New crossmember
Max deflection: 0.972”Max deflection: 0.897”
Loading #3—Results
Max eq. stress: 59.1 kpsiFactor of safety: 1.4
OEM crossmember New crossmember
Max eq. stress: 92.8 kpsiFactor of safety: 0.92
Mad stress concentration
Loading #3—Results
OEM crossmember New crossmember
Z (normal)
Neutral axis
Summary of Results
Safety factors
Load case OEM New
1 (shear) 1.8 2.5
2 (torsion) 11.3 9.7
3 (bending) 1.4 0.9
Model Limitations
• Difficult to model frame rail interaction—boundary conditions
• Difficult to know magnitude of loading conditions
• No detailed models of weld joints, body mounts, gussets, or rounds
Conclusion
Our simple analysis shows:
• The new crossmember is less stressed than the OEM version for typical “around town” loading conditions (load case 1)
• However, for extreme off-road type load conditions, the new crossmember is inferior to the OEM (load cases 2,3)
• Further analysis and prototype testing should be done before going into production.
What we learned
• 3D importing
• 3D meshing
• Effects of different boundary conditions
• FEA is not a “black box”
