Justin Wies
Senior Project
ANALYSIS
Appendix A1 shows the calculations for an impulse load of 400lbs. is shows that the impulse requires the device to withstand a force of 994.58lbs from above. Appendix A2 shows the impulse calculations for the side impact. It shows that the device must withstand a force of 1356.1lbs from the side. Appendix A3 shows the impulse calculations for an impact from below. It shows that the device must withstand a force of 1439.84lbs from the bottom. Appendix A4 shows the tensile force for the bolts from the bottom load. Appendix A5 shows the shear forces on the bolts generated by the bottom load. Appendix A6 shows the bending moment generated by the top load. Appendix A7 shows the bending moment for the impact from below. Appendix A8 shows the bending moment for the side impact. Appendix A9 is the calculations for the Moment of Inertia in the around the y-axis, Iy. Appendix A10 shows the calculation of the neutral axis in the x-axis. That was needed to calculate the moment of inertia in the x-axis, which is shown in Appendix A11. The moment of inertia in the x-axis was used to calculate the bending stress in the device to ensure the loads applied would not shear the device. The next page shows the maximum possible moment of inertia in appendix A12. This was used to quickly ensure that this project was possible. Appendix A13 shows the shear calculations for the side components. It uses the highest force to calculate the shear stress in the side tubing to ensure the side would not shear. Appendix A14 shows the shear stress calculations for the mount components. Appendix A15 shows the bending stress in the x-axis. It was proven that the device would not shear using a completely hollow device, so the maximum was unnecessary. Appendix A16 shows the bending stress in the y-axis. It proves that the bending stress will not exceed the ultimate shear stress of the material. Appendix A17 shows a calculation using the conservation of energy. This was proven to be insignificant as the calculation shows the “equivalent” static load for a 400lb person stepping on the device would be 8,348lbs. It was mutually concluded that using conservation of energy was inaccurate due to the losses in energy being neglected. Therefore the original way of calculating using momentum was used. All Appendix can be see at the end of the project report.
CONSTRUCTION
First all the parts for the step base will be cut to the correct length. Then the sides will be cut to length and cut to the correct shape. Then the base will be welded to the sides using TIG welding. Next the supports will be cut to the right length and welded into their positions. Then the supports will be welded inside the base in their correct positions. Next the flat bar and diamond plate tops will be welded over the top of the base. Lastly the mounts will be welded to the sides.
After further investigation the original mounting spots on the truck were not as rigid as originally thought to be. The project manager fixed this by designing supports that run from the bottom of the sides on the devices, back to the actual frame of the truck. They are bolted to the frame and the devices using the same mounting hardware used to mount the devices. These additional supports can be seen in Appendix B8.
Describe your image.
Describe your image.
Describe your image.
Describe your image.
Describe your image.
Describe your image.
The requirements for the tests are for the device not to yield under the maximum load, however it is not intended to test to failure. The areas of interest in the tests is the step sub assembly itself, for the first test specific steps will be taken to eliminate the deflection in the truck body, in the suspension, and the deflection in the mounts and supports. The first test will only measure the deflection in the step sub-assembly. The prediction for the first test is that it will have a significantly higher yield load than the requirement. To test the step sub-assembly first it will be supported with two jackstands, one under each end of the step. This will eliminate any other sources of deflection. Then an appropriate load will be applied to the top while the deflection is measured by a dial indicator against the step. The second and third tests will be the same principle and procedure as the first, they will just be measuring different sides of the device. The third test is a simple weight test, the device must weigh less than 35lbs ea. The device is also required to not yield under a load of 994.58lbs on the top of the step. It must not yield under a load of 1356.1lbs from the side, and it must not yield under 1439.84lbs from the bottom side.
The tests will essentially be applying appropriate loads to the step sub-assembly and then measuring the deflection from different sides and then correlating that into a failure load. The testing will happen this weekend, the weekend of the 7th of April and will probably last 10 hours total. The resources needed as stated above are a dial indicator with a travel of at least 1 in, Microsoft Excel, a scale capable of at least 50lbs, sandbags and miscellaneous hand tools. The project manager already has an extensive amount of tools including jacks and jackstands, and the load applied will be sandbags. The only safety concern for this test is the device could yield and cause injury, but the probability of that is extremely miniscule.
TESTING
The main deliverable for these tests are going to be the deflection of the device under load as indicated by the dial indicator from the different sides, as well as a scale weight. The deflection of each side will be correlated into a failure load for every side. When the calculated failure load is higher than the requirement, the device will pass.
The device passed the first three tests with impressive numbers. The device can withstand a force of over 3000lbs on the top, over 4100lbs on the side, and almost 2500lbs from the bottom which gives the device a factor of safety of 3.04, 3.04 and 1.71 respectively. The final test was the scale weight, the scale read the exact same number every test which was 30.0lbs. That is 5lbs under the requirement so again the device passed with impressive numbers.
In conclusion, all the tests were successful in testing the devices ability. The testing gave good numbers that were used to calculate yield loads for all three sides. The devices used were considered extremely accurate and held precision of +/- .0005. The calculated yield loads were all significantly higher than the requirements, which gave appropriate factors of safety. There is nothing that needs to be changed if these tests were to be repeated.The raw data and full analysis can be seen in the Test Report.
RESULTS
The device will be made of 6061-T6 aluminum alloy as stated before. Initial price checks put the budget at just under $500. Most of the parts were prices at OnlineMetals.com. The devices ended up being built for $387. This is well under the budget of $500. This included all the material for the devices, the material for the supports (which was free), and the mounting material. The detailed budget can be see in the appendix of the project report and in the spreadsheet below.
The schedule has been changed multiple times. In week four the project was almost cancelled out of nowhere. The Board of Advisors suddenly saw no engineering merit in the project. A week was wasted while convincing the Board otherwise. Shortly after that the project changed to include many more design requirements to ensure enough green sheets would be produced. At the end of week six, the project almost changed again when the Board decided the way the calculations were made needed to be different. So another week was wasted there determining that the Board was wrong. A detailed Gannt chart can be seen below in the Gannt chart and in the project report.