3D Beam Large Deflection Analysis

ME 501

Tim Allred

Jon Bell

June 20, 2001

Overview

• Objective• Problem Definition• Analysis• Results• What we learned• Conclusion

Project Objective

• Model this mechanism in 3D

• Compare deflection and stress results using large deflection analysis to:– Approximate 2D pseudo

rigid body model

– 2D beam model

– 3D beam model using small deflection analysis

Problem DefinitionOriginal Suspension Compliant Suspension

14.6

16

6.5

500 lbs.

Designed for 8 inches of vertical motion for 500 lb force input.

Cross-Sectional Shape

2.0 X 0.215 in.

Material: Carbon/Epoxy Composite

SUT: 330 ksi

E: 20.6 Mpsi

1

5

2

76

4

3

Analysis Models

• 2D beam large deflection

• 3D beam small deflection• 3D beam large deflection

9

8

76

5 4

321

Results  3D w/ large

displacements3D w/ small

displacements2D model Psuedo-rigid body

results

Displacement at node 7

9.7 inches 7.4 inches 8.6 inches 8 inches

Maximum Stress

182 ksi 171 ksi 177 ksi N/A

Displacements

   

3D large displacement model 3D small displacement model 2D model

9.7 “ 7.4 “8.6 “

Stresses

3D large displacement model 3D small displacement model 2D model

Stress distributions change

Stressmax=182 ksi Stressmax=171 ksi Stressmax=177 ksi

What we learned about ANSYS!• 2 Plane Bending• 3D beam Torsional Moment of

Inertia– With no input, ANSYS

automatically inserts polar moment of inertia or

Ixx +Iyy

• Maximum Stress includes only Bending + Axial Stresses– Shear Stress due to Torsion

not included– For correct failure analysis,

user would need to calculate shear stress by hand

MR

Conclusions

• 3D modeling with large displacement is necessary for accurate results on this particular problem due to the torsion introduced on the compliant member

• ANSYS is very useful in predicting results and learning about the important parameters of the problem

• Prototype would need to be built for accurate verification of results