The motivation of the work presented here is to include hands-on labs relevant to a finite element course, as well as labs that will help students to build skills sought by the industry. Hands-on laboratories are highly encouraged by ABET and results and surveys show that these type of labs help to keep students engage in this course. The hands-on projects included in this work aim to design a new version of a bracket minimizing its mass through the use of topology optimization.
The first step in the design optimization procedure proposed in this course is to get the geometry of an existing bracket using a laser scanner. In this step, students become familiar with laser scanners used in the industry for reverse engineering. Laser scanners are also used in metrology departments in industry to check the quality of finished products through dimensional analysis in a similar way as using a coordinate measuring machine. After the original geometry of the bracket is obtained students work with the model in a commercial finite element software.
The finite element method (FEM) is a standard tool used in the industry to verify new designs solving a variety of problems ranging from stress analysis; frequency analysis; heat transfer analysis; sound propagation; etc. The FEM consists of discretizing a continuum into small elements, where the properties of each element are defined in matrix form. Then the global matrices used to represent the equations of the problem for the whole continuum (structure) are built from the contribution of each of the element matrices. Commercial finite element software have also optimization tools including topology optimization that allows to minimize the mass of a structure, while keeping the maximum level of stress below the yield strength of the material preventing failure of the part. Thus, topology optimization is a very powerful tool with applications in the industry such as vehicle lightweighting. Finite element analysis require accurate representation of the material properties. In this case Young’s modulus and Poisson’s ratio were obtained from tensile/compression tests. These tests were carried out with 3D printed samples manufactured with different orientations.
The final design of the students’ brackets must be lighter than a design proposed by the instructor. The only information given to the students is the proportion of mass kept in the instructor’s final design. After students get their final bracket design, students have to manufacture a prototype of their bracket using a 3D printer. Finally, the last step in the design procedure is to carry out a tension or compression test of the bracket to validate the finite element analysis. An error of 10% between analyses and experimental tests is considered acceptable and an error less than 5% is considered excellent.
Surveys are also given to students to get feedback on how these labs help to keep students engage in the course. Results show that students enjoy working with commercial FEM codes and experimental work with average grades of 90%. In comparison the average grades of the exams is 70%.
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