1) Two mechanical engineering students designed a luggage tote for a manual wheelchair as part of a senior design project and performed finite element analysis in ANSYS to analyze stress and deflection. 2) When a 30-lb load was applied, the FEA predicted a maximum deflection of 1.63 inches, which occurred at the point where the load was applied. 3) The maximum von Mises stress of 37.14 ksi exceeded the yield stress of the 6061 T-6 aluminum alloy frame, but experimental testing found the deformation was completely elastic even with twice the load, suggesting the actual maximum stress is lower.

1. SOUTH DAKOTA STATE UNIVERSITY
ANSYS Final Project
Luggage Tote for a Manual Wheelchair
Danard Higgs, Ashim, Dahal, Sam Gould
5/4/2012
Course: ME 417/517
Professor: Dr. ZhongHu

2. Background / Purpose
Two of the group members, Danard and Sam, were working on a mechanical engineering
senior design project requiring some finite element analysis. The goal of the senior design
project was to design a luggage tote for a manual wheelchair as shown in Figure 1. The tote was
designed to hold 30 lbs with a safety factor of 2. The tote frame was constructed entirely out of
6061 T-6 aluminum alloy. The FEA was performed in ANSYS and involved finding the
maximum von Mises stress and deflection of the tote under various degrees of loading. The load
was applied at the corner of the tote furthest from the mounting pole (a.k.a. the “mast”) to
produce the worst-case deflection and internal stress.
Figure 1: Luggage Tote for a Manual Wheelchair

3. Deflection
To simulate the presence of the wheelchair and its rigidity, we simply created a 2-in
boundary condition which fixed the mast in the x, y, and z direction at the bottom of the mast.
Lastly, a 30-lb force over 91 nodes was applied in the downward (negative y-axis direction) as
shown in Figure 2.
Figure 2: Boundary Conditions and Load

4. For our FEA deflection analysis, there was a maximum deflection of 1.63 inches. This
maximum deflection occurred mostly at the point where the load was applied which was
expected. As the Figure 3 below shows, the deflection is distributed evenly throughout the mast.
The most distributed load deflection occurs along the front and left angle bar whilst the least
amount occurs on the right and back angle bar.
Figure 3: Deflection Only, 30-lb Load

5. The next three figures show the deflection with respect to the initial position of the tote at
various view angles. The black lines arranged in a grid represent the tote in its unloaded position
and the colored solid part shows the tote when it is loaded. The deflection is again 1.63 inches.
Figure 4: Deflection + Initial Position, 30-lb Load, View 1
Figure 5: Deflection + Initial Position, 30-lb Load, View 2

6. The deflection shown in the above three figures (but especially evident in Figure 6) is
exaggerated from real life due to differences in the area covered by the applied distributed load.
In ANSYS, we were able to apply a load on a smaller area toward the far corner, whereas in an
experimental setting the load was distributed more toward the middle of the tote.
In order to compare the behavior of the tote in ANSYS to that of the real-life
experimental setting, loads were applied from 0 – 60 lbs in 5-lb increments in ANSYS and the
deflections were plotted. This was compared to the same set of data collected experimentally.
These deflection curves are illustrated in Figure 7. As one can see, both the ANSYS and
experimental curves follow a close-to-linear pattern. However, the curve of the experimental
deflection has a lesser slope. Once again, the difference here is probably due to how the load was
distributed in ANSYS versus how it was able to be distributed in real life. In the experimental
setting, the weight was distributed closer to the center of the tote rather than the far edge, which
would result in lesser deflection for any given amount of weight.
Figure 6: Deflection + Initial Position, 30-lb Load, View 3

7. Figure 7: Deflection Curves
Stress
The stress that was exerted by the 30-lb load is shown in the figures below at different
view angles. The yield stress for the 6061 T-6 aluminum frame was 24 ksi. The most common
level of von Mises stress exerted on the tote was about 8.25 ksi, which provided a safety factor of
2.9. This exceeds the desired safety factor 2.0, which is great but may be slightly too high for this
application. However, this prevents a careless user of the product from doing harm to the tote.
0
0.5
1
1.5
2
2.5
3
3.5
0 10 20 30 40 50 60 70
Deflection(in)
Weight (lb)
ANSYS
Experimental

8. Figure 8: Von Mises Stresses, View 1
Figure 9: Von Mises Stresses, View 2

9. The maximum stress for this tote was 37.14 ksi, which admittedly exceeds the yield
stress. This means that if the tote was to fail, it would fail in this particular area. The area where
the maximum stress occurs can be seen in Figure 10 in the small area shown below. However, it
is speculated that the maximum stress is actually less than 37.14 ksi and the reason for such a
high calculated stress is due to limitations in the finite element grid size. In an experimental
setting, the deformation of the tote frame is completely elastic even with twice the load
experienced in ANSYS—that is, 60 lbs.
Figure 10: Location of Maximum Stress