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Results:
Above: Rob Graves checking data acquisition results for cyclic tensile loading Three major tests were performed on the combination fatigue tester. The first of the three tests analyzed the vertical load portion of the tester. The second analyzed the tensile loading portion of the tester and the third analyzed the optical encoders ability to collect cycle data. All test data was gathered utilizing a LabView program written by Kevin Garvey, a graduate student at Florida State University, and load cells. It should be noted that the program was setup to test individual components. With this being said only one load cell could be tested at a time. If the fatigue tester was actually being used for testing a need for data from both load cells, simultaneously, would be necessary. A screenshot with critical testing features is displayed below.
Tensile Load: Figures 4-2 and 4-3 display the load cycle exhibited by the electromagnet used for applying tensile loading. One volt (y-axis) is equal to approximately 22 lbf. The timescale (x-axis) is centi-seconds. Thus the graph displays a load of approximately 1.54 lbf being applied at a rate of 4 Hz. This load was being applied with a 12 V power source driving the electromagnet. This demonstrates that the combination fatigue tester was successful at applying a cyclic load. It should be noted that a maximum of approximately 5 lbf was achieved with the 12 V power source. Figure 4-3 displays a force of approximately 10 lbf being applied at a frequency of approximately 1 Hz.
Vertical Load:
Figure 4-1 shows the constant load applied by the vertical load assembly. The display shows a force of approximately 7 lbf. The cause of the constant change in amplitude was not determined. One cause for concern was the fact that the voltage, and in turn load, steadily decreased. After roughly 4-5 minutes steady state was reached. This leads us to believe that there are unaccounted forces such as friction present. This is likely due to the components of the vertical load. For vertical load, cyclic loading conditions are not necessary. The rotation of the specimen produces the cycle. 
Optical Encoder: Figure 4-5 displays the optical encoder output. Many issues were encountered when attempting to properly mount and aligning the optical encoder, which led to several tests. Eventually useful data was acquired. A simpler encoder disk would be preferable. The one used has multiple channels which can be read, and which can lead to inaccurate cycle counts. For the needs of this machine, only a single channel is required to count once per rotation.
Recommendations:
The final design of the Cummins 2 combination fatigue tester proved, on a small scale, to have many effective design components. It should first be mentioned that many components were designed with the constraints of limited machining and limited budget. It should also be noted that there are several proven ways to accomplish several of our goals, i.e. tensile and bending loading, many of which were disregarded due to the aforementioned constraints. With all of this said, if the design mentioned throughout this report were to be manufactured for industrial use several issues would need to be addressed. Listed below are recommendations for these issues.
-Fabrication of critical parts, i.e. shafts and specimens, should be machined with high tolerances in order to ensure alignment. -Grip design, tapped for use with a threaded specimen, may be prone to misalignment issues. Exploration of others grip designs is recommended. -For tensile fatigue testing a load cell should be placed in-line with the specimen. -Programming to control the distance of the magnet from the steel plate should be implemented in order to maintain constant tensile loading force. -Replace the steel plate used for magnet attraction with a metal that has a higher permeability such as Mu-metal. -Vibration analysis should be performed in order to determine necessary dampening controls. -All data acquiring instruments, i.e. load cells, should have low error. -Methods for cycle count need to be addressed. -A more powerful magnet that can apply minimal load of 1500 lbf at a distance of .005 in. is recommended. -Utilize a function generator to control electromagnetic force as opposed to on-off power cycler. -Implementation of a safety cover should be fabricated to protect operator during testing. -A physical cutoff switch should be added to the tester.
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