SOUTH DAKOTA STATE UNIVERSITY

ANSYS Final Project

Luggage Tote for a Manual Wheelchair

Danard Higgs, Ashim, Dahal, Sam Gould

5/4/2012

Course: ME 417/517Professor: Dr. Zhong Hu

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

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

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

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

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

0 10 20 30 40 50 60 700

0.5

1

1.5

2

2.5

3

3.5

ANSYSExperimental

Weight (lb)

Defle

ction

(in)

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.

Figure 8: Von Mises Stresses, View 1

Figure 9: Von Mises Stresses, View 2

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