Drawing

DEPCOllc
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3305 Airport Drive | Pittsburg, KS 66762
E7
Follow these steps to use the flexural formula to answer the question “Will it break?”
1. Run the GEARS-TrebStar simulation using
the given parameters.
2. Record the value for ( P ), the maximum
(Dynamic) load on the axle from the
GEARS-TrebStar trebuchet simulator. The
maximum dynamic load value,
max(Fax/Fcw) =, can be found on the
lower right corner of the GEARS-TrebStar
interface. See the red circle in the adjacent
figure. The
max(Fax/Fcw) value is the r
of the maximum dynamic load to the
counterweight mass. To calculate the
maximum dynamic load, multiply the
max(Fax/Fcw) value by the counterweight.
atio
3. Use the flexural formula to calculate the
maximum allowed stress, S
max
for the
specified axle radius ( r ). Note: L and r are
given in the preceding parameters list.
4. Compare the calculated maximum allowed stress for the axle to the given yield strength
for the type 304 steel axle material.
Example: An Explanation of the Preceding Problem.
1. Run the trebuchet design parameters through the GEARS-TrebStar simulator to determine the
maximum dynamic load ratio,
max(Fax/Fcw) = 3.5. When this value is multiplied by the
counterweight the resulting maximum dynamic force on the axle is 3.5 x 2.2lbs = 7.7lbs ( P ).
2. The axle radius ( r ) is 0.118 inches.
3. The Axle span is ( L ) is 3.94 inches, rounded off to 4 inches.
4. Substitute the values for P, r and L in the flexural equation to determine the maximum allowable
stress for this axle system.
3
max
r
L
P)
1
(S 
S
3
max
0.118in
4in.
7.7lbs)
3.142
1
(S 
2
max
in/lbs7.6126S
5. Comparing the allowable stress for the axle (6126.7psi) to the yield strength of the material
(30,000psi) indicates an axle design with a margin of safety of nearly 5:1. This axle is certainly
adequate for this application.
Sample Engineering Curriculum
Analyzing the Stress on the Trebuchet Axle continued