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Hands on Lab Demonstration to Teach how Mechanical Properties Change Due to Cold Working and Recrystallization

Abstract Laboratories that employ hands-on demonstration to change material properties play an important role in understanding why materials are selected for different design specifications. Engineering students take courses in mechanics of material, machine design, finite element analysis and capstone senior projects. These courses require students to call out and specify the best and least expensive material according to some type of chemical, physical or mechanical loading conditions. Students should understand the way a material behaves in service depends upon its alloy composition, crystalline structure, manufacturing process and heat treat condition. This paper is written after developing a hands-on material lab that teaches engineering students how cold work and recrystallization processes affect material properties. The driving force for this hands-on lab came from the “ABET course level loop assessment action” outlined in appendix A. Its main focus is with yellow brass and copper, however, other metallic materials can be used and explored by the same procedure outlined in the lab handout. The first part of the lab requires students to set up a heat treat furnace. They anneal yellow brass and measure hardness values at different soak times. By plotting the data of hardness versus log time in minutes will show the three unique stages of the recrystallization process. The second section of the lab teaches how the cold working process changes mechanical properties. Students receive test coupons of copper to cold work to different percentages. Hardness and dimensional values are measured and the data are plotted to generate material behavioral curves. A series of questions in the lab handout helps reinforce the theory taught in the class room to this hands-on learning process. Introduction Metals are commonly used in many design applications because of their strength and ductility properties. Cast irons, tool steels and ceramics are some examples of materials that can exhibit high strength but very low ductility. These materials have very little to no plastic region on a stress strain diagram. Ceramics and glasses can even fracture well below the ultimate tensile strength of the material. This is caused by stress concentrations and the lack of ductility that does not allow the state of stress to relax within the geometric discontinuities.

Ductility is a measure of plastic deformation and is a required material property for joining, extruding, swedging, drawing and forging operations. Introducing the metal to some mechanical and/or thermal manufacturing processes can easily alter the material properties of strength, hardness and ductility. The processes of work hardening at room temperature and annealing are two common manufacturing processes that typically change mechanical properties of metallic materials.

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Magda, D. (2009, June), Hands On Lab Demonstration To Teach How Mechanical Properties Change Due To Cold Working And Recrystallization Paper presented at 2009 Annual Conference & Exposition, Austin, Texas. 10.18260/1-2--5484