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Enhancing Combined Stress Laboratory Learning Opportunities

William K. Szaroletta Purdue University, West Lafayette, Indiana

Abstract: Combined stress theory coupled with laboratory practice has improved student comprehension in both a sophomore-level mechanics of materials and an upper-level experimental mechanics course. The Combined Stress lecture has traditionally developed the theory from free body diagram through beam deflection, with related homework problems providing analytical practice. Similarly, the Combined Stress laboratory has traditionally provided students an opportunity to experimentally and analytically verify and validate the combined stress theory. Good correlation between theoretical and experimental results was frequently obtained through the utilization of a carefully machined C-Clamp with strain gage instrumentation. However, the twist method of introducing axial and bending loads to the inside and outside surfaces of the beam portion of the C-Clamp instrumented strain gages limited both the accuracy and the amount of data that could be collected within a standard 110-minute laboratory session.

Recent Combined Stress laboratory upgrades have included introducing a load cell transducer, 3D modeling, Finite Element Analysis (FEA) and utilizing data acquisition (DAQ) hardware and software. The voltage output of the load cell can be directly correlated to the clamping force and provides a useful, new experimental baseline result. The FEA analysis outputs, at various load levels, provide a new analytical baseline result. Together, these new experimental and analytical baseline results have provided students significant new learning opportunities as they compare and contrast these results with their traditional analyses of the experimentally-obtained strain measurements. The DAQ has provided much improved granularity of test data in roughly the same timeframe with increased repeatability. Together, these upgrades have facilitated increased understanding of combined stress theory, introduced modern experimental methods in both lecture and laboratory, provided the students two new baselines against which to compare and contrast, given students a finer granularity data set upon which to base their analyses, and enhanced student experiences with technical report writing. This paper includes both an overview of the Combined Stress theory, analysis techniques, and traditional laboratory procedures and details of the success of the Combined Stress laboratory upgrade, operation, and outputs.

Introduction: Magill1 designed and implemented a combined bending and axial loading experimental mechanics laboratory using a C-Clamp that produced exceptional correlation between theoretical and empirical results. Improving on this laboratory was difficult as the lab was simple and had few drawbacks. Coyle2, et al presented an innovative derivative of Magill’s combined stress experiment utilizing a hacksaw instead of a C-Clamp. There are few drawbacks with Magill’s present C-Clamp laboratory. The upgrades of the combined stress laboratory to include data acquisition (DAQ), provide other analysis alternatives, introduce strain gage rosettes,and address some minor drawbacks were the primary motivations for the applied research presented in this paper.

Proceedings of the 2002 American Society for Engineering Education Annual Conference & Exposition Copyright Ó 2002, American Society for Engineering Education

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Szaroletta, W. (2002, June), Enhancing Learning Opportunities In A Combined Stress Laboratory Paper presented at 2002 Annual Conference, Montreal, Canada. 10.18260/1-2--10048