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In many engineering situations, load-bearing members are exposed, either intentionally or unintentionally, to electrical currents. This topic, the effect of electricity on the mechanical properties of a material, has not been investigated. Furthermore, laboratory set-up and procedures designed to investigate these effects have not been designed and published for incorporation into typical material science courses. Therefore, in order to begin to identify these effects and to broaden the scope of the traditional laboratory experiments associated with standard materials science courses, a test apparatus was developed that allows hardness measurements to be collected from metallic specimens while varying the levels of current that are passed through the specimen. The fixtures and the material specimens that were used for the testing were carefully designed and developed so that they could accept the electrical current. Also, the safety and effectiveness of the fixtures were two primary considerations. The electrical current had to be isolated from both the person conducting the tests and from the Rockwell hardness testing machine. The tests were conducted by supplying an electrical current to the metallic test specimens. At that time, a hardness reading was taken and recorded. Hardness readings were taken at various levels of electrical current. Since the electrical current raised the temperature of the specimens, the laboratory was designed such that students can study the effect of temperature on the hardness of a material and isolate the effect of the electricity from the effects due to temperature changes. Worksheets were developed to aid in the recording of the data collected. Information such as calibration, hardness readings, electrical current, and specimen temperature was recorded. In this paper, the fixture and specimen designs were provided, along with the laboratory objectives, set-up, procedure, analysis and results. Introduction The goal, of the laboratory experiments that are incorporated into a material science course, is to expose students to the various techniques by which material properties are obtained and to help the students understand the various factors that may influence these properties. Page 970.2 “Proceedings of the 2004 American Society for Engineering Education Annual Conference & Exposition Copyright © 2004, American Society for Engineering Education" In most design situations, it is the mechanical properties of a material that drive the design process, these properties tend to be the focus of the laboratory experiments. Traditionally, these properties are first established through a series of simple tension, compression, shear, impact, and hardness tests. These first laboratories are designed to aid students in understanding how the “typical” value of each mechanical property is obtained. Once the students have gained an understanding of how the baseline is established, most material science laboratory courses begin a series of tests to help students understand the factors that influence this baseline. These laboratories usually include experiments that focus on the effect of temperature, strain rate, alloys, cold work, and microstructure. These experiments effectively cover many of the traditional design situations that starting engineers will face. However, with the large and ever-growing electro-mechanical industry, these existing laboratory experiments do not cover a major area of importance: the effect of electricity on the mechanical properties of a material. In 1969, it was first reported that electric current pulses reduce the flow stresses in metals 1 . Since that time, research has demonstrated that current can affect both simple and complex mechanical properties and phenomenon of metals in many ways. For instance, research by Xu et al. demonstrated that continuous current flow can enhance the recrystallization rate and grain size in select materials 2 . Further work by Conrad demonstrated that other mechanical properties are also affected by electrical current flows 3,4,5 . However, in depth investigations of the effects that electricity has on the overall mechanical properties of a material have not been considered. Furthermore, laboratory set-up and procedures do not currently exist and the results are not published concerning the expected effects of electricity on these overall properties. Due to this fact, the results obtained through this investigation cannot be directly compared to results previously published. However, by running several materials and also by comparing the results from these materials to the established effects of temperature on the hardness of each material, the validity of the testing apparatus and procedure can be established. Considering the effect that electricity can potentially have on the mechanical properties of a material, a technique has been developed and is presented herein that will allow the effect of electricity on the hardness of a material to be investigated as part of a typical material science laboratory. The set-up and procedure presented below is designed to be the first exercise in a series of laboratory experiments that will be designed for dual research/laboratory use that will allow the effects of electricity on the mechanical properties of a material to be fully investigated as part of a traditional materials science laboratory course. By using different materials each semester in the laboratory and recording the results over several years, a general database of the affects on various materials can be developed. These results can then be used for design purposes where electricity may pass through a material while under load. The laboratory objectives, testing set-up, and procedure are all presented, along with techniques for recording, analyzing, and interpreting the data. The hardness of a material was chosen for several reasons. First, the hardness of a material provides a quick insight into the strength and wear resistance of a material without requiring a lengthy testing time. The students have a limited amount of time in the laboratory to investigate the effect of the electricity on the material, therefore, a shorter testing time allows for a greater P ge 970.3 “Proceedings of the 2004 American Society for Engineering Education Annual Conference & Exposition Copyright © 2004, American Society for Engineering Education" range of electrical currents and materials to be investigated. Furthermore, due to the mechanical nature of a hardness test, these machines are relatively easy to isolate without a high risk of injury to students or damage to the equipment. Laboratory Objectives and Parameters The objective of this laboratory was to establish the effect of electrical current on the hardness of various materials. Since the electrical current directly causes an increase in specimen temperature, the effect of current was investigated with and without compensating for specimen temperature increases. The current was passed through each specimen from 0 amps to 800 amps. Three material specimens were investigated: aluminum, hot rolled steel and stainless steel. Multiple hardness measurements were taken at each current level and the specimen’s temperature was recorded. Hardness measurements were taken on a new specimen at corresponding temperatures generated through the use of a furnace for the purpose of comparison. Laboratory Test Set-up There were 5 components of the laboratory test set-up: fixtures, temperature measurements, electrical supply, the hardness testing machine, and safety. Figure 1 presents a schematic of the test equipment and Figure 2 is a schematic of the fixtures. Figure 3 shows a picture of the actual experimental set-up for reference purposes. Figure 1 Schematic of the Test Equipment P ge 970.4 “Proceedings of the 2004 American Society for Engineering Education Annual Conference & Exposition Copyright © 2004, American Society for Engineering Education" Figure 2 Schematic of the Test Fixtures Figure 3 Overall View of Testing Machine and Fixtures P ge 970.5 “Proceedings of the 2004 American Society for Engineering Education Annual Conference & Exposition Copyright © 2004, American Society for Engineering Education" Fixtures When designing the fixtures that held the hardness testing indenters and test specimens, the primary concerns were that the fixtures could not distort the hardness measurements nor conduct electricity. To handle these restrictions, a 6” x 6” ceramic tile was epoxied between the original indenter holder and the new indenter holder (refer to Figures 2 and 4). Another 6” x 6” ceramic tile was epoxied between the original anvil holder and the new specimen holder. The ceramic tile is clearly visible in the figures due to its light-green color. The ceramic tiles were used to ensure that the electricity was not conducted through the Rockwell hardness testing machine. The new indenter and specimen holders were precisely machined and assembled to minimize the effects on the hardness readings. Also, to minimize the effects on the hardness readings, the epoxy, used to create the new indenter and specimen holders, was applied and allowed to dry under the same load that the fixtures undergo during testing. The indenter holder was machined very similar to the original indenter holder, and the specimen holder side was machined to securely hold the test specimens with straps and wing-nuts. Since a large torsional force was created by the electrical supply cables, after mounting the cable clamps to the test specimens, straps and wing nuts were used to secure the test specimens to the anvil of the hardness testing machine. The specimens were also used to securely hold the test specimens during the testing. Figure 4 Fixtures to insulate the Rockwell Hardness Tester from the Electrical Supply P ge 970.6 “Proceedings of the 2004 American Society for Engineering Education Annual Conference & Exposition Cop

Broadening The Scope Of A Materials Science Course By Experimentally Testing The Effects Of Electricity On A Metallic Test Specimen’s Material Properties