Tensile Comparison of Polymer Specimens Produced with Different Processes

The tensile test identifies key mechanical properties of materials, making it a common element in many materials science laboratory classes. In the sophomore-level mechanics course for the mechanical engineering technology (MET) degree program and the introductory materials and processes courses for MET and manufacturing engineering technology (MFET) students at campuses of University, tensile testing of dogbone specimens made by a single manufacturing process has been in place for many years. As is, this testing provides an effective means for lower division college students to understand how mechanical properties such as Young’s modulus and ultimate tensile strength are determined. However, the variability in apparent and actual property values that comes from differences in manufacturing processes and dimensional tolerances leads to student confusion and lack of confidence in their experimental results. To help lower division college students understand how these factors affect experimental results, the tensile testing experiment was expanded to incorporate thermoplastic specimens made by three distinctly different processes. Student roles included manufacture of the specimens, measurement of necessary dimensions, conducting the tensile tests, generating stressstrain curves for each specimen, and determining the corresponding Young’s modulus and ultimate tensile strength values. Reflection on the effects of process and geometric variation on their property results became a new report requirement. This article will present the complete laboratory experience, results, and initial student response to this enhanced tensile testing experiment.