1. Structure Analysis of 6061-T651 Aluminum Bridge Team Blackboard Mechanical Engineering University of Rochester Team Blackboard Department of Mechanical Engineering Rochester, NY 14627-0132 teamblackboard@me.rochester.edu The Members of team Blackboard Sam Selonick Kevin McNelis Chris Babcock Nick Stadnyk This work is supported by The University of Rochester Mechanical Engineering Research Department under the direction of Prof. David Quesnel † We work best under pressure. The objective of this project was to design a bridge and maximize its figure of merit (the total supported load divided by the bridge weight) such that the structure that would span an 8” chasm and allow a 5” wide by 3” tall object to bass below its deck. This bridge was constructed using 6061-T651 aluminum sheet metal and 1/8” aluminum pop rivets. Under maximum load, the bridge should have a maximum of.1” deformation and remain suspended off the ground. To start designing a solution to this task, our group made preliminary sketches and basic cardboard models to obtain a better understanding of the load distribution and subsequent deflections of the beams. From these tests, we drew the conclusion that an I-beam structure with a top sheet metal brace could handle maximum load without the use of too much material. A CAD of our final sketch was then made in ANSYS Workbench and tested with an approximate load of 500 pounds centered across the middle of the bridge deck, where the loading beam would rest. From the post-processing data we found the optimum areas for rivet placement, such that they were in the places of lowest stress concentration; as well as the stresses and deformations involved in the loading of the structure. Both parts and assembly drawings were then made and submitted for machining. The final analysis of the constructed bridge will be a load test of the bridge suspended above the chasm with 2 group members balancing on a plank centered about the bridge deck. A real value for figure of merit can then be recorded and used to determine the effectiveness of the structure. Executive Summary The People Presentation: 12:30 pm – 1:30 pm Monday, December 13, 2004 May Room, Wilson Commons, University of Rochester Bridge operation and material constraints outlined. Paper and pencil methods for minimizing deflection discussed. Results of ANSYS stress analysis reviewed and construction parameters determined by location of maximum and minimum stress concentrations. Conclusion that only one type of bridge material used, 6061-T651 selected for its high stiffness and relatively low weight. All parts and overall assembly drafted and depicted, with all aspects of design laid out in detail. Summary ANSYS Analysis Material Properties For further Information and technical discussion, contact: Test Setup I-Beam bridge Table 8” Loading bar Design The experimental setup is depicted above. Our bridge design was initially tested element by element using the Equivalent Stress theory to optimize the beam lengths. This theory was used to make sure that the bridge did not deflect any more than the.1” requirement. Aluminum 6060-T651 Material Properties Hardness, Brinell95 Hardness, Knoop120 Hardness, Rockwell A40 Hardness, Rockwell B60 Hardness, Vickers107 Tensile Strength, Ultimate45000 psi Tensile Strength, Yield39900 psi Elongation at Break12 % Modulus of Elasticity10000 ksi Notched Tensile Strength47000 psi Ultimate Bearing Strength88000 psi Bearing Yield Strength56000 psi Poisson's Ratio0.33 Fatigue Strength13800 psi Fracture Toughness26.4 ksi-in½ Machinability50 % Shear Modulus3770 ksi Shear Strength29700 psi The values for various aluminum properties are found in the table to the right. The high stiffness of 6061-T651 and low density.098 lb/in 3 as well as high machinability made it the perfect material choice for the task. Aluminum pop rivets, with a 1/8” diameter, were used rated with an ultimate tensile stress at 240 lbs. and a breaking point stress at 400 lbs. Pop Rivet 3 2 1 3 1 Equivalent Stress Plot: Max stress = 3.085E4 psi Safety Factor: Ranges from 1.0 – 15.0 the safety factor is high, and bridge may have been overbuilt in certain areas. Total Deformation Plot Plot Displaying Spot Weld Placement The max yield for the material used to build the bridge is 40.6 ksi. Our distortion theory plot (equivalent stress plot) gave us a value of 3.085E4 psi. Comparing the two shows that when placed under 500 lbf of force, the bridge does not reach the max yield point where it would break. Also comparing our value to the tensile strengths, it is apparent that the bridge is operational under this condition, seen in the safety factor. The figure of merit obtained by dividing the weight held by the bridge ( experimentally 500 lbf) by the weight of the bridge itself, which was found to be.87742 lbm. The figure of merit for this weight is therefore 569.85. The bridge is expected to hold much more weight though, and this figure will be higher. Analysis Interpretations