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Session 1426 Behavior of Materials at High Temperatures; Instilling a Healthy Uncertainty

Daniel W. Walsh, Ph. D., David Gibbs, College of Engineering, California Polytechnic State University, San Luis Obispo

The events that occur in metallic materials heated to high temperatures determine material functionality, formability and fabricability. Few laboratory experiences allow engineers to explore the performance of real engineering materials at homologous temperatures greater than 0.8. Fewer still enable students to relate material performance at these temperatures to the microstructure of the material. Moreover, the relationship of material properties at lower temperatures are rarely graphically and directly connected to the conditioning of a material at higher temperatures. This paper describes the conception and execution of a laboratory experience to improve undergraduate students understanding of these complex material behaviors. In addition it includes portions which enable the student to quantify phenomena often discussed only in qualitative fashion. Laboratory procedure for the experiment is described in detail.

In this laboratory, students accomplish hot ductility testing using the Gleeble thermo-mechanical simulator, a system that has been successfully used to characterize the behavior and cracking susceptibility of numerous alloy systems. Students identify two key parameters of cracking sensitivity, the Nil Strength Temperature (NST) and the Nil Ductility Temperature (NDT) for alloy systems they test. Students pull samples to failure on heating to the NST and on cooling from the NST. Students record strength and ductility of each sample. This approach provides quantitative strength and ductility data under thermomechanical conditions which approximate industrial environments. Students examine fractured samples using scanning electron microscopy (SEM), optical microscopy (OM) and electron microprobe analysis (EMPA).

The laboratory allows students to observe changes in the mechanical properties of materials as a function of temperature. Students treat materials in rapidly changing environments which closely mimic those encountered in application, rather than in the mock contexts often discussed in the classroom or oversimplified cases typically treated in the laboratory. The laboratory discussed presents theory and application in a natural fashion, linked and mutually supportive. The paper discusses the exceptionally positive impact that this immediacy has an on student learning.

I. Introduction The behavior of materials at elevated temperatures is a crucial but often ignored segment in the educational journey of many engineers. This is problematic as engineered systems will often be exposed to high homologous temperatures either during fabrication or when in service. Typically, curricular exposures to the high-temperature behavior of materials are limited to brief theoretical treatments in textbook readings or lecture. Laboratory experiences that treat elevated temperature Proceedings of the 2004 American Society for Engineering Education Annual Conference and Exposition Copyright © 2004, American Society for Engineering Education

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Walsh, D. (2004, June), Behavior Of Materials At High Temperatures Paper presented at 2004 Annual Conference, Salt Lake City, Utah. 10.18260/1-2--13266