June 14, 2015
June 14, 2015
June 17, 2015
26.1437.1 - 26.1437.17
Students’ Struggles to Explain Atomic Behavior of Metals in a Tensile Test LabIn traditional mechanical tensile test labs, engineering students interact with macroscale samples,and while they learn about dislocation motion and slip from their readings or from lectures, theyhave no opportunity to directly explore the atomic-level behavior of metals. The representationsthey are exposed to are often static figures, or at best a simplified animation depicting dislocationmovement. This low level of interaction with the concepts results in students having difficultyexplaining the atomic-level processes that lead to plastic deformation, or why slip planes are atan angle from the tensile axis. While a nanoscale tensile test simulation has been used in arequired sophomore level materials laboratory course for a number of semesters, the integrationwith the traditional tensile test lab has not realized an optimal impact on students’ learning. Toimprove the integration of the traditional tensile and nanoscale simulation components of thetensile test lab, a better understanding of the concepts that students struggle with as a result of theexisting integration must be investigated.Sophomore materials engineering students performed, analyzed, and compared results from botha traditional tensile test of metals and a molecular dynamics simulation tensile test of a nanowire.The latter was performed using the Nano-Materials Simulation Toolkit on nanoHUB.org.Students’ lab reports and responses to a related exam question were qualitatively analyzed.When students compared the macro- and nanoscale test results, they did not tend to makereference to the characteristic features of stress-strain curves. That is, many did not explicitlycall out differences or similarities in the values of the Young’s modulus, the yield strength, theultimate tensile strength, or the segments of the stress-strain curve indicating the elastic andplastic regions. Students were distracted by thermal noise in the nanoscale stress-strain curvesthat was absent from the macroscale tests.From the exam question analysis, it was evident that students did not have enough practicecomputing the characteristic features of stress-strain curves. For instance, they confused Young’smodulus with yield strength.In both the lab report and the exam question, many students could repeat phrases they had reador heard concerning dislocation motion and slip, but they struggled to associate those phraseswith concepts or with the characteristic features of either the macroscopic or nanoscale stress-strain curves or the atomic images generated by the simulation.Based on the results of this study, a number of revisions were recommended to better capitalizeon the simulation component of the lab. First, greater explanation of the input parameters andthe outputs of the simulation are needed so that the simulation is treated less like a black box.Second, directions need to be incorporated into the analysis of the results to ease comparison ofthe mechanical and simulation tests, both standardizing the presentation of the resulting stress-strain curves and pointing students to look at the characteristic features. Third, students need tobe directed to conduct some analysis of the atomic motion that is visible in the simulationimages.
Diefes-Dux, H. A., & Coughlan, A., & Johnson, D. R., & Douglas, K. A., & Faltens, T. (2015, June), Students’ Struggles to Explain the Atomic Behavior of Metals in a Tensile Test Lab Supported by a Molecular Dynamics Simulation Paper presented at 2015 ASEE Annual Conference & Exposition, Seattle, Washington. 10.18260/p.24774
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