June 14, 2015
June 14, 2015
June 17, 2015
26.1653.1 - 26.1653.20
Using Additive Manufacturing and Finite Element Analysis in a Design-Analyze-Build-Test ProjectAdditive manufacturing (AM) equipment has become increasingly available to engineeringprograms over the last two decades. At _______ University, AM has been used to supportstudent projects from freshman design classes to capstone projects. This paper discusses adesign-analyze-build-test project that uses AM to supplement instruction in finite elementanalysis. Variations of the project have been used with both high school and upper-divisionundergraduate students.The project involves the redesign of a simple bracket. The bracket is attached to a wall with fourscrews and must support a vertical load applied several inches away from the wall. As anadditional design requirement, the bracket will have a conduit passing through it from side toside, and so there is a region of the bracket that must remain clear of obstructions. A baselinedesign that includes two supporting ribs with large holes for the conduit path is presented to thestudents. The students follow step-by-step instructions to model the baseline design withSolidWorks software. They then use the SolidWorks Simulation Finite Element Analysis (FEA)program to apply boundary conditions and loads, mesh and run the static (linear) analysis, andview the stress and deflection results. A baseline bracket fabricated by additive manufacturing isthen tested for deflection under a specific load and then loaded to failure. Based on the analysisand test results, students are then tasked to redesign the bracket, with the goal of producing thelightest design that meets deflection and strength requirements subjected to several geometricconstraints.With high school students, the students are advised to remove material where the stresses are lowand to add material where the stresses are high. We have found that the students can grasp theconcept of stress reasonably well, without getting into the details of the failure criterion used topredict yielding. We introduce the concept of stress concentrations, which is demonstrated byhigh localized stresses near the holes in the ribs. The fact that the baseline bracket fails at thishigh-stress location provides a correlation between analysis and testing for the students. Afterallowing the students to work individually on the bracket redesign, we form groups of two orthree students and allow them time to discuss their ideas and produce a design that we will buildand test. The testing of the brackets provides a fun competition to conclude the project, andafterwards we discuss the results, focusing on both the usefulness and the limitations of theanalysis. Students are surveyed before the tests to determine how well they understand theconcepts of FEA, and after the tests to determine whether observing the tests and discussing theresults enhances their understanding.The bracket project has also been adapted for use in a one-credit elective course, Advanced SolidModeling and Analysis, offered to upper-division undergraduate students. The project serves asan introduction to nonlinear analysis, as the ultimate failure load is much higher than the load forwhich yield is first predicted with linear analysis. Results from tensile tests of the AM material(ABS plastic) are used to define the non-linear properties. Another important lesson of theproject is that idealized boundary conditions do not always adequately simulate actualdisplacements. After watching the back plate pull away from the wall between the screwattachment points, students realize that assuming that the back plate is fixed will not allowaccurate prediction of displacements. While some students produce designs that are similar inappearance to the baseline, the lightest design that met all of the requirements was radicallydifferent from the others. The significance of this result is that as AM becomes a viablemanufacturing option for more industries over the next decade or two, the constraints that designengineers face will be different. This project encourages students to use more creativity in thedesign process.This project is an example of how additive manufacturing can be used to supplement instructionin finite element analysis. While verification of FEA results by comparison with closed-formsolutions is valuable, physical testing of the articles being analyzed highlights effects such asnonlinear (both material and geometric) behavior and inconsistent boundary conditions that arenot apparent in the closed-form solutions.
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