(HPV) shown below and on the next page for their Senior Design project and raced it at the 2012 ASME HPV East Competition. The design was good in many regards but its fatal flaw was that the front axles bent (i.e., yielded due to static overload) during the competition. For this problem, you will calculate the factor of safety of the front axles. Assume the following: The weight of the vehicle was about 90 lbs, and the weight of the largest rider was about 180 pounds.
The total weight was distributed equally among the three wheels (two front, one rear). The front axles were cantilevered from their mounting points on the control arms to the wheels (see figure at lower right on the next page), with a distance of about 3.75 inches from the fixed end to the point where the load from the wheel was applied. The axles were 1 inch in diameter. The axles were made of a cheap ductile steel, with a tensile yield strength of perhaps 24,000 psi. Because this failure mode is quite significant, use a conservative failure theory. Axles like these do not rotate; the bearings and the wheels rotate about them. Because this is a static load on a ductile material, you need not consider stress concentration.
a. First, determine the factor of safety the way the team did, by considering only the stress created in the axle by direct shear. Determine the stress, then find the principal stresses, then apply the failure criterion to determine the factor of safety.
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0. Next, determine the factor of safety based on consideration of the bending normal stresses in the axle. Again, determine the stresses at the critical point, then find the principal stresses, then apply the failure criterion to determine the factor of safety.
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