June 15, 2019
June 15, 2019
June 19, 2019
Experimentation and Laboratory-Oriented Studies
Beam bending is one of the foundational concepts that is critical in several fields including mechanical engineering, aerospace engineering, and civil engineering. At the authors’ institution, the topic is treated thoroughly in a lecture-based, sophomore-to-junior level class in strength of materials (mechanics of materials.) Still, many students come to the topic of mechanics of materials courses with significant pre-conceptions and misunderstandings that make it difficult to overcome through lecture material alone (Brown, et al, JEE, 2018). Indeed, when students are shown that their preconceptions are faulty, it enhances their retention of the correct material and has the ancillary benefit of developing their critical thinking skills in other engineering topics.
There are many laboratory experiments that focus on beam bending but they fall into two main categories. Experiments that take place in dedicated instructional labs and which make use of sensors to obtain detailed, quantitative data on beam bending. Such labs can study beams in different types of loading, and are helpful in allowing students to compare measurements to theoretical predictions. Another category of experiments uses hand-held demos to show qualitative behavior. The main advantage of these types of teaching aids is that they are inexpensive, portable, and can be used within classroom lectures as a means of just-in-time reinforcement of concepts. The goal of this research project is to create an experimental platform that is a compromise between the two extremes. A student team was charged with designing and building a prototype, which is being used presently in the mechanics of materials course at the authors’ institution. The platform is portable, but is also instrumented with strain gauges, displacement actuators (turn screws), and rotational sensors. Data acquisition is accomplished using a National Instruments myDAQ and a laptop computer running Matlab. The device is designed to accept beams of different materials and cross-sections, and can apply loading in different ways.
The experiment was intentionally designed to target students’ misconceptions about stress and strain. In particular, experimental exercises were developed to show how choice of materials can influence strain, but not stress under identical loading situations. Conversely, displacement loading of beams having different materials produces the same strain, but different stresses. Finally, the effect of the cross-sectional symmetry is investigated to yield quantitative and qualitative data about beam twist resulting from point loading. The platform plus all the instrumentation is purposely designed to be very portable, robust and simple to understand by students in ME, AE, and CE courses. Similar to (Pickel et al, ASEE, 2016), student engagement is reinforced through use of post-demo analysis of the quantitative data.
The paper will describe the experimental platform. It will also focus on the design of the learning exercises used in the classroom. Finally, preliminary results will be presented based on a concept inventory conducted pre-experiment and post-experiment.
Ferri, A. A., & Craig, J. I., & Ferri, B. H., & Alemdar, M. (2019, June), Development of a Portable Experimental Platform to Demonstrate the Role of Material and Cross-section in Beam Bending Paper presented at 2019 ASEE Annual Conference & Exposition , Tampa, Florida. https://peer.asee.org/32649
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